Plant-availability of soil and fertilizer zinc in cultivated soils of Finland Markku Yli-Halla University of Helsinki Department of Applied Chemistry and Microbiology FIN-00014 UNIVERSITY OF HELSINKI, Finland Academic dissertation To be presented, with thepermission of the Faculty of Agricultureand Forestry of the University ofHelsinki, for public criticism in Auditorium XII, Aleksanterinkatu 5, Helsinki, on October Ist, 1993,at 12 o’clock noon. https://www.c-info.fi/en/info/?token=eOP7BRNzCAdYJmqe.PJUYcyoN0Vzgld2er7wASA.pb77xkRwj1XkJ0gFjV6RVsODLAvrG6zMwIvbmggJUvEPZDBtvOgI3o10xoFFUzDFPWMB6SVxq7N6Z3RDVzxRGQKl9U5tKUae5Xogu8FKuXWNWQQNeBYnBEIripDR1pQwT-C5kS3FItoEZC7RTt6yKfcAoygwHFC7TynfLp6KJLDOj2ahfNhwgcqFQ6TVhqZKn8jorEbYw2dsJGatn5JO_QIoF8Aa6iQFiaVY65L3Jtau--bGe9ZXfRovnaRomdNcxNYmrt4EBw PREFACE The experimental part of this study was mainly carried out at Kemira Oy Espoo Research Centre in 1987 - 1992,and the work was finalized in 1992 - 93 at the University ofHelsinki, Section ofAgricultural Chemistry and Physics of the Department of Applied Chemistry and Microbiology. 1 wish to thank Mr. Donald Jonasson, Vice president ofR&D, Dr. Aino- Maija Evers, Dr. Simo Kivisaari and Mr. JormaSyvälahti atKemira Oy, for offering me the financial and institutional framework which facilitated this investigation. I also thank Dr. Antti Jaakkola, Professor of Agricultural Chemistry and Physics, for allowing me to join his section at the University to complete this study, and for his guidance and constructive criticism at the various stages of the work. I am grateful to Dr. Helinä Hartikainen, Professor ofSoil and Environmental Chemistry, and Docent Erkki Kemppainen for checking my work. My thanks are extended to the staff of the former Agricultural Department of Kemira Oy Espoo Research Centre both at Suomenoja and at the Kotkaniemi Experimental Farm for technical assistance in the experiments. My warmest thanks are due especially to Mrs. Saara Sinisalo whose expertise was indispensable in the laboratory and to Mr. Esko Viikari who skilfully took care of the field experiments. I also thank the district sales representatives ofKemira Oy who provided me with part of the soil samples used in this work. I would also like to thank the technicians of the Section of Agricultural Chemistry and Physics at the University for helping me complete the analytical work. The figures were drawn by Ms. Hillevi Tenninen and the English manuscript was revised by Mrs. Sevastiana Ruusamo, M.A. and editedby Mrs. Sari Torkko, M.Sc., to whom I express my appreciation for their work. This study was finan- cially supported by the Scientific Foundation of the Finnish Association of Academic Agronomists (Agronomien Yhdistyksen tieteellinen säätiö), for which I express my sincere gratitude. Finally, I would like to thank the board of Agricultural Science in Finland for accepting this study to be published in their journal. Helsinki, May 1993 Markku Yli-Halla 201 CONTENTS ABSTRACT 203 1 INTRODUCTION 204 2 METHODS OF ANALYSIS 205 2.1 Testing the methods of soil Zn determination 205 2.1.1 Total Zn 205 2.1.2 Fractionation of soil Zn 206 a. Water-soluble and exchangeable Zn 207 b. Zinc bound by organic matter 208 c. Zinc bound by sesquioxides 209 d. Repeated pyrophosphate extraction 210 e. Reproducibility and additivity of the results of sequential extractions 210 2.2 Chemical and statistical analyses 211 2.2.1 Determination of Zn 211 a. Total Zn and chemically specific fractions of Zn in soil 211 b. Procedures used in soil fertility testing 212 c. Zinc in plant material 212 d. Zinc in fertilizers 213 2.2.2 Other analyses 213 2.2.3 Statistical methods 213 3 ZINC IN SOIL 214 3.1 Experimental soils 214 3.2 Zinc in surface soil 215 3.2.1 Total Zn 215 a. Soil samples 215 b. Particle size fractions 217 3.2.2 Fractions of soil Zn 218 a. Water-soluble and exchangeableZn 218 b. Zinc bound by organic matter and sesquioxides 218 c. ComplexedZn 219 d. Residual Zn 220 e. Relationship between Zn fractions and other soil properties 220 f. Distribution of soil Zn into different fractions 221 3.2.3 Zinc extracted by AAAc-EDTA 222 3.3 Vertical distribution of soil Zn 223 3.3.1 Total Zn 224 3.3.2 Zinc extracted by AAAc-EDTA 225 3.4 Extractability ofZn added to soil 225 3.5 Discussion 227 3.5.1 Total Zn 227 3.5.2 Fractions of soil Zn 228 3.5.3 AAAc-EDTA extractions 230 4 AVAILABILITY OF SOIL AND FERTILIZER ZINCTO RYEGRASS IN POT EXPERIMENTS 231 4.1 Availability of soil Zn 231 4.1.1 Experimental 231 4.1.2 Dry matter yields 232 4.1.3 Zinc concentration and uptake 232 4.1.4 Dependence of Zn uptake on soil properties 234 4.1.5 Utilization of soil Zn reserves 235 202 4.2 Effect of Zn application on plant Zn concentration 239 4.2.1 Experimental 239 4.2.2 Dry matter yields and plant Zn concentrations 239 4.2.3 Influence of soil characteristics on the response to applied Zn 240 4.2.4 Response of ryegrass to applied Zn in soils poor in ZnAc 242 4.3 Effect of liming and different rates of Zn application on ryegrass 243 4.3.1 Experimental 243 4.3.2 Dry matter yields and plant Zn concentrations 244 4.3.3 Atmospheric deposition of Zn in the greenhouse 247 4.3.4 Soil analyses at the end of the experiment 247 4,4 Discussion 248 5 FERTILIZERS AS ZINC SOURCES INPOT AND HELD EXPERIMENTS 250 5.1 Experimental 250 5.1.1 Fertilizers 250 5.1.2 Experiments with ryegrass and timothy 251 a. Comparison of Zn fertilizers in apot experiment 251 b. Application of Zn fertilizers to timothy in the field 252 5.1.3 Field experiments with barley 252 a. Comparison of Zn fertilizers 252 b. Application of different Zn rates 253 5.1,4 Weather 253 5.2 Comparison of Zn fertilizers, Zn rates and application practices with grass crops 254 5.2.1 Effect of Zn fertilizers on ryegrass in apot experiment 254 5.2.2 Effect of Zn fertilizers on timothy in the field 255 5.3 Comparison of Zn fertilizers, Zn rates and application practices with barley 257 5.3.1 Different fertilizers as Zn sources for barley 257 5.3.2 Plant Zn concentration as affected by different Zn rates 258 5.4 Discussion 259 6 GENERALDISCUSSION AND CONCLUSIONS 262 REFERENCES 264 SELOSTUS 270 APPENDICES 1-9 Plant-availability of soil and fertilizer zinc in cultivated soils of Finland Markku Yli-Halla Yli-Halla, M. 1993. Plant-availability of soil and fertilizer zinc in cultivated soils of Finland. Agric. Sci. Finl. 2: 197-270. (Dept. Appi. Chem. Microbiol. FIN-00014 University of Helsinki, Finland.) The Zn status of cultivated soils of Finland was investigated by chemical analyses and bioassays. The effect on ryegrass of different Zn fertilizers and Zn rates was studied in pot experiments and their effect on barley and timothy in field experiments. In an uncontaminated surface soil material of72 mineral soils and 34 organogenic soils, total Zn (Zntot) was 10.3 - 202 mg kg" 1 (median 66 mg kg" 1 ). In mineral soils, Zntot correlated positively with clay content (r = 0.81 ) and in organogenic soils negatively with organic C (r = -o.s3***). Zinc bound by organic matter and sesquioxides was sequen- tially extracted by 0.1 M K4P207 (Znpy) and 0.05 M oxalate at pH 2.9 (Znox), respect- ively. The sum Zn py + Znox,0x, a measure of secondary Zn potentially available to plants, was 2 - 88% of Zntot and was the lowest in clay (median 5%) and highest in peat soils (median 49%). Water-soluble and exchangeable Zn consisted of0.3 - 37% (median 3%) of Zntot, the percentage being higher in acid soils, particularly in peat soils. Zinc was also extracted by 0.5 M ammonium acetate - 0,5 M acetic acid - 0.02 M Na2-EDTA at pH 4.65 (ZnAc), the method used in soil testing in Finland. The quantities of ZnAc (median 2.9 mg dm" 3 , range 0.6 - 29.9 mg dm" 3 ) averaged 50% and 75% of Znpy + Zn0x in mineral and organogenic soils, respectively, and correlated closely with Znpy . In soil profiles, ZnAc was with few exceptions higher in the plough layer (0 - 20 cm) than in the subsoil (30 - 100 cm). In an intensive pot experiment on 107 surface soils, four crops ofryegrass took up 2 - 68% (median 26%)of Znpy + Zn ox.0 x. The plant-available Zn reserves were not exhausted even though in a few peat soils the Zn supply to grass decreased over time. Variation of Zn uptake was quite accurately explained by ZnAc but increasing pH had a negative impact on Zn uptake. Application of Zn (10 mg dm" 3 of soil as ZnSCri • 7H20) did not give rise to yield increases. In mineral soils, increase of plant Zn concentration correl- ated negatively with soil pH while ZnAc was of secondary importance. In those organo- genic soils in which the reserves of native Zn were the most effectively utilized, plant Zn concentration also responded most strongly toapplied Zn. In two 2-year field experiments, Zn application did not increase timothy or barley yields. Zinc concentration of timothy increased from 30 mg kg" 1 to 33 and 36 mg kg" 1 when 3 or 6 kg Zn ha 1 was applied, respectively. The efficiency ofZnSCri ■ 7H20 alone did not differ from that ofa fertilizerwhere ZnSCfi • 7H20 was granulated with gypsum. Zinc concentration of barley grains increased by foliar sprays ofNa2Zn-EDTA but only a marginal response to soil-applied Zn (4.8 or 5.4 kg ha" 1 over three years) was detected in three 3-year experiments. High applications of Zn to soil (15 or 30 kg ha’ 1 as ZnSCXt • 7H20) were required to increase Zn concentration ofbarley markedly. In order to prevent undue accumulation of fertilizer Zn in soil, it is proposed that Zn fertilizer recommendations for field crops should be based on both soilpH and ZnAc. In slightly acid and neutral soils, even if poor in Zn, response of plant Zn concentration to applied Zn remains small while there is a high response in strongly acid soils. Key words; soil analysis, vertical distribution of soil Zn, pot experiments, field experi- ments, liming, plant Zn concentration, barley, ryegrass, timothy 203 Agric. Sei. Finl. 2 (1993) 1 INTRODUCTION Zinc is a trace element, the average concentration ofwhich in the earth’s crust is quoted as 70 mg kg' 1 (Wedepohl 1991). There are minerals containing Zn among olivines and pyroxenes, e.g. acmite- augite, and amphiboles, e.g. riebeckite. Also 2:1 clay minerals, mainly trioctahedral micas, contain Zn owing to isomorphic substitution of Mg or Fe ions for Zn at octahedral sites (Rankama and SA- hama 1950,Lindsay 1972, Huang 1989). A sub- stantialpart of total Zn in soil occurs in clay and silt size particles (Shuman 1985), and total Zn content correlates with the content of clay or clay plus silt (Sippola 1974, Schlichting and Elgala 1975, Tjell and Hovmand 1978, Baghdady and Sip- pola 1983,Liang et al. 1990). Zinc is released into the soil solution from mineral structures through weathering reactions as Zn2+ cation which is fur- ther adsorbed by various soil constituents and util- ized by living organisms. The significance of Zn as a nutrient of higher plants was shown in 1926by Sommer and Lipman. Zinc is involved in several enzymatic reactions of protein and carbohydrate metabolism of plants (Marschner 1986). Zinc deficiency in crop pro- duction is extensive in calcareous soils (Sillanpää 1982), but insufficient Zn supply to dryland crops occurs also in acid soils for example in several states of the USA (Junus and Cox 1987, Boswell et al. 1989),Brazil (LINS and COX 1988), Australia (Brennan and Gartrell 1990) and Zambia (Banda and Singh 1989).Zinc deficiency induced by liming has also been reported (Kowalenko et al. 1980,MACNAEiDHEetaI. 1986,Myhr 1988). In Finland, the average Zn concentration of timothy ranges from 24 to 32 mg kg' 1 (Lakanen 1969, Kähäri and Nissinen 1978) and in cereal grains from 26 to 36 mg kg' 1 (Jaakkola and Vogt 1978, Varo et al. 1980)although means as high as 54 mg kg' 1 have been reported in cereals (Pessi et al. 1974, Syvälahti and Korkman 1978). The Zn concentration in the crops ofFinland is above the minimum physiological requirement ofgramineous plants or clover, 10-20 mg kg' 1 of plant dry matter (e.g. Marschner 1986,Brennan and Gartrell 1990, Carsky and Reid 1990). Hence Zn applica- tions have not increased yields in field experiments with cereals and forage crops (JAAKKOLA and Vogt 1978, Syvälahti and Korkman 1978, Sil- lanpää 1990). However, Zn concentration of crops grown in Finland is almost always below 50 mg kg' 1 , a desirable level in the fodder of ruminants (NJF 1975, Salo et al. 1990). Worldwide, annual industrial consumption of Zn ranks fifth among metals after Fe, Al, Mn and Cu (Kabata-Pendias and Pendias 1984). In Finland, 160 000 tons ofZn is manufacturedannually (Tilas- tokeskus 1992), and 20% is consumed in the do- mestic markets mainly in galvanization (S. Karlman 1991, Outokumpu Oy, pers. commun.). Zinc is dispersed in the environment as emissions of metal industry and through the use of Zn-con- taining products. Elevated contents of Zn are found in soils of industrial areas, especially around Zn mines (Bergholm and Steen 1989), smelters (An- derssonand Nilsson 1976,Elsokkary and Låg 1978, Miller and McFee 1983), along highways (DeLaune et al. 1989), under electric pylons (Al ■ Hiyaly et al. 1990) and in urban areas in general (Salomons 1984) owing to trafficand combustion of fossil fuels (Cass and Mcßae 1983). Sludge application also gives rise to elevated Zn contents of soil (Wiklander and Vahtras 1977, CHRISTIE and Beattie 1989). Atmospheric deposition of an- thropogenic origin is considered a major source of Zn input to the soil ofrural areas in southern Swe- den and western Norway (ÖBLAD and Selin 1986, Steinness et al. 1989). The annual precipitation in southern and central Sweden and Finland is 100 - 140 gZn ha' 1 (Ross 1987, Erviö et al. 1990) and an increasing accumulation ofZn in lake sediments of Finland has been observed during the last 100 years (Myllymaa and Murtoniemi 1986,Verta et al. 1989). Zinc input into the cultivated soils ofFinland has probably increased over time, but intensified culti- vation has elevated Zn uptake by the crop espe- cially in grasslands (Rinne et al. 1974). A decrease of soil Zn concentration in northern Finland has been observed in timothy fields when the same fields were analyzed in 1974 and again 14 years 204 Agric. Sei. Fint. 2 (1993) later (ErviÖ et al. 1990).This has been regarded as an indication of gradual decline of plant-available Zn in intensive grassland cultivation. Also farm- level observations indicate insufficient supply of Zn to crop or domestic animals. Grasslands on peat soils have commonly shown poor growth after 10 years of intensive cultivation, and Zn deficiency has been suggested as an explanation to this (Urvas and Soini 1984). In northern Finland, cat- tle have exhibited symptoms of Zn deficiency which disappeared with Zn injections. One way of contributing to a sufficient Zn supply to the cattle would be the elevation of the Zn content of forage crops and fodder cereals by Zn fertilization. Zinc fertilization is in Finland recommended es- pecially to fodder crops (Viljavuuspalvelu 1992). Before 1982, less than 30 000 kg ofZn (below 15 g ha 1 ) was applied annually in mineral fertilizers. The first macronutrient fertilizer (18-3-12% N-P- K) containing also 0.3% Zn was introduced in 1982 and a separate granular Zn fertilizer in 1984. Since 1982, 180 000 - 420 000 kg, or 80 - 210 g Zn ha' 1 has been spread annually in mineral fertilizers, more than 90% ofwhich incorporated in macronu- trient fertilizers (Kemira 1992). The principal areas of fertilizer Zn consumption have been the prov- inces ofVaasa, Mikkeli, Kuopio and especially the provinces of Oulu and Lappi where 500 g Zn ha' 1 , as compared to 20 - 50 g ha' 1 in the southernmost provinces, has been applied annually in chemical fertilizers. Even though field experiments on Zn fertilization have been carried out in Finland, the influence of soil characteristics on the response to applied Zn has not been investigated previously. Neither has the efficiency of different commercial Zn fertilizers been compared. The purpose of the present investigation was to examine the content and solubility of Zn in culti- vated soils ofFinland and the effect of Zn fertilizers on cultivatedplants. Information on the soil charac- teristics controlling the solubility and plant-avail- ability of native and added Zn was sought. The study did not concentrate on soils suspected to be poor in Zn; the soil material collected represented all kinds of cultivated soils ofFinland. The empha- sis was in the plough layer, but the vertical distribu- tion of Zn was also investigated. In addition to the characterization of soil Zn by soil analyses, the availability of soil Zn was studied in a pot experi- ment. The effect of Zn application on the Zn con- tent of forage was examined in pot and field experi- ments. Also barley, the most important fodder ce- real in Finland, was included in the field experi- ments. The ability of soil analysis to explain Zn uptake by ryegrass and to predict the response of plant Zn concentration to Zn applications was criti- cally studied in pot experiments. In field experi- ments, the efficiency of different Zn fertilizers and application methods were compared, not forgetting environmental aspects. 2 METHODS OF ANALYSIS 2.1 Testing the methods of soil Zn determination Soils from a material of 13 cultivated soils (Appen- dix 1) were mainly used for testing the methods of soil analysis. A few soils from a larger material (Appendix 2) were occasionally used. 2.1.1 Total Zn In order to determine the total Zn content (Zn tot) in the soil, the solid matrix needs to be dissolved. Hydrofluoric acid (HF) is required for complete decomposition of silicate minerals, and perchloric acid (HClOa) is a strong oxidizing agent for organic materials. Procedures with and without these haz- ardous chemicals were tested for the digestion of Zntot. In the aqua regia procedure (1), a 300-mg soil sample (four replicates) was digested with 4 ml of aqua regia (AR, 1 ml of concentrated HNO3 and 3 ml of concentrated HCI). The sample was heated for2 hours in a platinum crucible on a hot plate and 205 Agric. Sei. Finl. 2 (1993) allowed to react overnight. The next morning the residue was washed with warm dilute HCI into a volumetric flask. In the procedure ofLim and JACK- SON (1982) employing aqua regia and HF (2), a 300-mg soil sample (four replicates) was digested with 4 ml of AR for 2 hours at 200°C in a 100-ml volumetric flask in a sand bath. Thereafter, 5 ml of HF was added and digestion was continued for 1 hour after which 50 ml of saturated H3803 was added to dissolve the possibly precipitated metal fluorides. After cooling, the bottle was filled with deionized water. In the HNO3 - HF - H2SO4 proced- ure (3), a 500-mg soil sample (four replicates) was digested with 20 ml ofHNO3 in a teflon crucible on a hot plate until dry. Then, 5 ml ofH2SO4 and 15 ml of HF were added and evaporated to dryness. In order to completely remove fluoride, 5 ml of concentrated H2SO4 was added and evaporated to dryness. The residue was washed into a volumetric flask withwarm dilute HCI. From three soils, AR dissolved 55 - 70% of the quantity of Zn dissolved by the two mixtures containing HF (Table 1). In an experiment with 12 surface soils (4, 11, 23, 30, 32, 35, 60, 61, 67, 69, 88, 105 in Appendix 2), the effect of HCIO4 addition was tested in the Table 1. Soil Zn dissolved by aqua regia (AR), AR-HF and HNOrHF-H2 S04.' Soil Zn (mg kg l) dissolved by AR AR-HF HNOrHF- h2 so4 209 Very fine sand 46.0b 82.8“ 82.8a 211 Fine sand 40.3b 72.1“ 70.1“40.3b 72.1 a 70. l a 212 Mull 50.2b 76.4“ 71.7“ 1 Results of each soil were tested separately. Means marked with the same superscript do not differ at P = 0.05. Table 2. Recovery of Zn added to a mull soil (212) digested according to the HNOrHCI0 4-HF-H 2S0 4 procedure. l Zn addition Zn Recovery of added Zn mg kg- 1 mg kg-' mg kg-' % 0 74.9< 50 122.7" 47.8 96 100 168.6» 93.7 94 1 Means marked with different superscripts differ at P = 0.05. 206 HNO3 - HF - H2SO4 procedure. After the digestion with HN03,3 ml ofHCIO4 and 3ml of H2SO4 were added and warmeduntil fumes evolved and heating was continued for 10 more minutes. Then, HF and H2SO4 were added as describedabove. Inclusion of the additional digestion phase into the procedure increased the average quantities of Zn extracted from 82.2 to 84.6 mg kg' 1 (+2.9%). According to the paired t-test, the difference was not statistically significant (t = 1,856n s ), but in further digestions also HCIO4 was added in order to ensure effective oxidation of organic matter. An experiment was carried out to study possible Zn loss and contamination during the digestion pro- cedure. Portions (500 mg) of carefully homogen- ized mull soil (212) were weighed into nine teflon crucibles. Next, 1) 10 ml of water, 2) 5 ml of a solution containing smgZn dm as ZnSOa • 7H20 (ZnSOq) plus 5 ml ofwater and 3) 10 ml of the Zn solution were pipetted into three crucibles each. The quantities of Zn added were 0, 50 and 100 mg kg' 1 of soil, respectively. The soil samples were digested according to the HNO3 - HCIO4 - HF - H2SO4 procedure as described above, and the Zn concentration in the digests was determined. No marked net loss or contamination occurred during the digestion (Table 2). 2.1.2 Fractionation of soil Zn In order to characterize the chemical forms of soil Zn, it is commonly separated into fractions differ- ing in solubility. The fractionation makes the basis for the estimationof potentially mobile Zn reserves and availability ofsoil Zn to plants. The sizes of the fractions are defined operationally as quantities of Zn which are extracted, often sequentially, with solutions supposed to displace Zn from the ex- change complex or dissolve certain soil compon- ents resulting in a solubilization of Zn retained by them. The following fractions are commonly distin- guished: (1) Zn in the soil solution, (2) exchange- able Zn, (3) adsorbed, chelated or complexed Zn, (4) Zn in secondary clay minerals and insoluble metal oxides, and (5) residual Zn bound by primary minerals (VIETS 1962). Agric. Sei. Fin!. 2 (1993) There are no specific extractants for Zn, but vari- ous solutions are used for a simultaneousextraction of several elements, e.g. Zn, Cu, Mn, Fe, Al, Ni, Co. The sequential extraction procedures are usually combinations of single extraction methods devel- oped earlier for specific purposes. The most fre- quently applied procedure in non-calcareous soils utilizes neutral salt solutions (e.g. 0.05 M CaCb, 1 M MgCb) to extract water-soluble and exchange- able Zn, pyrophosphate solutions (0.1 M K4P207 or Na4?207) for the extraction of Znbound by organic matter, and ammonium oxalate - oxalic acid solu- tions for the dissolution of Zn bound by Fe, Al and Mn oxides (sesquioxides). This procedure was first used for the fractionation of soil Cu (McLaren and Crawford 1973) and has later been used also for the fractionation ofZn in non-calcareous soils (El- sokkary and LÅG 1978, IYENGAR et al. 1981, Bjerre and Shierup 1985, Haynes and Swift 1985,LIANG et al. 1990). H202 or NaOCI may be used instead of pyrophosphate for the dissolutionof Zn bound by organic matter (Shuman 1979, Nielsen etal. 1986,Sims 1986, Singhetal. 1988). A common feature for all the fractionation proced- ures is that residual Zn (Znre s), remaining in the soil after removal of oxide-bound Zn and consisting mainly of Zn in the primary minerals, is dissolved with concentrated acids according to the same pro- cedures as used in the digestion ofZntot- The same fractionation procedure is seldom used in more than one study, which complicates the comparison of results. Depending on the research objectives, different fractions are determined. In some studies a fraction of Zn supposed to be speci- fically adsorbed on inorganic sites has been ex- tracted by 2.5% acetic acid (Elsokkary and LÅG 1978, Iyengar et al. 1981, Bjerre and Shierup 1985)orPb(NO,3)2(Liangetal. 1990). Further,Zn bound by Mn oxide has been extracted together with Zn bound by Fe and Al oxides (Elsokkary and LÅG 1978,Shuman 1979) or separately (Sims and Patrick 1978, Iyengar et al. 1981, Miller and McFee 1983, Shuman 1985, Sims 1986, Liang et al. 1990). Zinc bound by poorly crystal- line Fe and Al oxides can be extracted separately from Zn bound by crystalline oxides (Miller and McFee 1983, Shuman 1985, Sims 1986) as op- posed to extracting only one fraction, referring to Zn bound by oxide materials. In addition to differ- ences in the extracting solutions, the same soil sample may be used throughout the procedure (El- sokkary and Låg 1978, Shuman 1979, Nielsen et al. 1986) or after the determinationof water-sol- uble and exchangeable Zn a new sample is weighed for the determination of the more sparingly soluble secondary fractions (Sims and PATRICK 1978, Iyengar et al. 1981). In the present study, MgCb solution was used for the extraction of water-soluble and exchangeable Zn, K4P207 for the extraction of Zn bound by organic matter and oxalate for the dissolution ofZn bound by Fe, Al and Mn oxides. The residual Zn was digested by the HNO3 - HCIO4 - HF - H2SO4 procedure. a. Water-soluble and exchangeable Zn Zinc cations (Zn2+ ) can be retained by the negat- ively charged sites by non-specific electrostatic forces. This fraction of Zn is exchangeable with other cations. For theoretical reasons, Mg 2+ salts have been considered suitable in the extractants for exchangeable Zn 2+ because the two cations are similar in radius and charge. It is therefore sup- posed that Mg 2+ effectively displaces exchange- able Zn 2+ from soil surfaces into the solution. Water-soluble Zn is simultaneously extracted. The 1 M MgCb was first used for the determination of plant-available Zn by Stewart and Berger (1965) and Martens (1968). In those days, con- centration of Zn was measured colorimetrically. Since the 1970’5, Zn has invariably been deter- mined by atomic absorption spectrophotometry (AAS) where a high salt concentration in the solu- tion analyzed may cause a high background absorp- tion as well as crusting of the burner. Owing to low concentration of Zn in the extract, dilution as a means ofreducing the salt concentrationmay not be feasible. Therefore the use of less concentrated salt solutions as extractants would be desirable. The effect of MgCl2 concentration on the extrac- tion of Zn from eight soils (201, 203, 204, 206, 209 and 210 in Appendix 1; 10 and 73 in Appendix 2) was studied. Soil samples (10 g, two replicates) 207 Agric. Sei. Fint. 2 (1993) were shaken for 2 hours with 25-ml aliquots of 1 M or 0.5 M MgCh solution. The suspensions were filtered and analyzed for Zn. The means and ranges of Zn extracted (mg kg' 1 ) were as follows: Solution Mean 1 M 1.71 Range 1.71 1.2-2.7 0.7 - 2.00.5 M 1.13 The less concentrated solution extracted 65% (range 53 - 74%) of that extracted with the 1 M solution. According to the paired t-test, the differ- ence between the quantities of Zn extracted with the two solutions was highly significant (t = 14.758 ), but the results correlated closely (r = *** 0.99 ). The mean deviation of the two replicates was 5.2%,range 0.3 - 22.2%. The recovery of added Zn was studied on the extract obtained from soil 201 with 0.5 M MgCl2 at the soil-to-solution ratio of 1:5 (weight/volume, w/v). Into three 180-ml portions of the extract, obtained by combining extracts of several sub- samples, 20-ml aliquots of water or solution of ZnSOa were added to produce concentrations theor- etically differing by 0.05 and 0.20 mg Zn dm'3 . The measured concentrations (four subsamples) showed accurate recovery of added Zn (Table 3). h. Zinc hound by organic matter The use ofpyrophosphate solution as the extractant for Zn bound by organic matter is based on the ability of pyrophosphate to solubilize humic sub- stances (Bremner and Lees 1949, Mortvedtand Osborn 1977) and on the ability of pyrophosphate anion to form soluble complexes with Zn (Asher and Bar-Yosef 1982, Bar-Yosef and Asher 1983). It has been hypothesized that polyvalent cations complexed to organic matter are respons- ible for keeping organic matter in a flocculated and water-insoluble state. These cations can be re- moved by complexing with pyrophosphate anion, resulting also in the solubilization of humus (STE- VENSON 1982, p. 40). However, the mechanism responsible for the solubilization of humic sub- stances and cations in the pyrophosphate extraction has not been fully established (BoRGGAARD 1988). Recovery of Zn added into the pyrophosphate extracts of a mull soil (212) was studied. Soil samples were shaken with 0.1 M K4P207 (pH 10) at the soil-to-solutionratio of 1:25 (w/v) for 18hours, and the suspensions were centrifuged. Zinc was added to the extracts as has been described earlier.Added Zn was accurately recovered (Table 3). The commercial K4P207 chemical contained 6 mg Zn kg' 1 resulting in aZn concentration of 0.2 mg dm'3 in the 0.1 M solution. It is possible to purify the reagent with a solvent extraction (Shu- man 1979) or with a cation exchange resin (SHU- MAN 1985). However, the reagent may be used withoutpurification ifZn in the extraction solution remains completely in the liquid phase during the extraction. The influence of Zn in the pyrophos- phate reagent was indirectly examined with four surface soils (Appendix 2) by studying the adsorp- tion of added Zn to soil suspended in the 0.1 M K4P207 solution (pH 10). In the experiment, 2.5-g soil samples (four replicates) were shaken for 18 hours in the following solutions: 1) MK4P2O7 2) 0.1 M K4P207 + 0.2 mg Zn dm'3 as ZnCl2 3) 0.1 M K4P207 + 0.4 mg Zn dm'3 as ZnCh Table 3. Recovery of Zn added to 0.5 M MgCl 2, pyrophosphate and oxalate extracts. Zn addition MgCl 2 ' Pyrophosphate 2 Oxalate 2 mg dm 1 Zn, mg dnr3 Recovery, % Zn, mg dm-' Recovery, °7o Zn, mg dnr' Recovery, % 0 0.02 - 0.15 - 0.34 0.050.07 98 - - - - 0.200.22 101 0.35 102 0.54 100 0.40 - - 0.55 101 0.75 101 1 Extract of soil 201 2 Extract of soil 212 208 Agric. Sei. Fin!. 2 (1993) Table 4. Effect of Zn addition to the pyrophosphate solu- tion on the concentrations of Zn measured in the soil extract. Soil Zn added to Zn in the Recovery of the extracant, extract, added Zn mg dm ' mg dnr 3 ~~ I ~~ mg dm 3 °/o 18 1 0 0.11 Clay 0.200.31 0.20 98 loam 0.390.50 0.39 99 34' 0 0.23 Loam 0.210.45 0.22 101 0.450.69 0.45 100 78' 0 0.29 Mull 0.240.53 0.24 100 0.460.76 0.47 102 104 1 0 0.84 Carex 0.241.09 0.24 103 peat 0.461.35 0.51 111 1 Soils from the surface soil material (Appendix 2) Zinc additions to the extractant corresponded to 4.1 - 9.2 mg Zn kg" 1 of soil and were recovered in the extract (Table 4), showing that added Zn was not adsorbed by the soil. The results are in agree- ment with those ofAsher and Bar-Yosef (1982) who observed that at pH 9 Zn was not adsorbed onto a Ca-montmorillonite suspended in a 0.0096 M pyrophosphate solution containing 8.0 mg Zn dm'3 . It can thus be concluded that Zn of the com- mercial chemical is not adsorbed either but only gives rise to a high background absorption. The 0.1 M K4P207 was therefore used in the extraction of Zn without purification. c. Zinc hound by sesquioxides Since the work of Tamm (1922), acid oxalate solu- tions have been widely used for the extraction of Fe and Al oxides in soil. In the dark, acid oxalate is supposed to extract only poorly crystalline oxides; in UV light, also crystalline Fe oxide is extracted. The oxalate solutions are assumed to dissolve com- ponents occluded into the Fe and Al oxides, and oxalate has therefore been used for the extraction of soil Zn. To avoid crusting of the burner of AAS, a 0.05 M oxalate solution was selected instead of more concentrated solutions commonly used in the fractionation procedures. The extraction ofZn from four soils with 0.05 M oxalate solutions was investigated at pH 2.0, 2.9, 3.3 and 4.0. The pH values were created by differ- ent ratios of oxalic acid and ammonium oxalate. Before the oxalate treatment, the samples (2.5 g, four replicates) were extracted with pyrophosphate and washed with water. The remaining samples were shaken for4 hours with 50-ml aliquots of the four oxalate solutions, the suspensions were centri- fuged and the extracts analyzed for Zn. The solu- tion which had the lowest pH was the most efficient extractant for Zn (Table 5), probably owing to a substantial dissolution ofstructural Zn. There was a considerable decrease in the extractability of Zn in three soils with an elevation of pH from 2.0 to 2.9, but an additional increase in pH affected the results less markedly. A solution of pH 2.9 (0.024 M and 0.026 M in oxalic acid and ammonium oxalate, respectively) was used in the rest of the oxalate extractions. The recovery of Zn added to the oxalate extract obtained from a mull (212) was studied. Prior to oxalate extraction the soil samples (2.5 g) were shaken with pyrophosphate and washed with water. The remaining samples were shaken in 50-ml ali- quots of0.05 M oxalate (pH 2.9) for 4 hours and the suspensions were centrifuged. Zinc was added to Table 5. Soil Zn extracted by 0.05 M oxalate at different pH values. 1 Soil Zn (mg kg ') extracted at pH 1151),,,, 2.02.9 3.34.0 mg kg ' 201 Fine sand 3.1» 2.4" 2.1 bc 2.CK 0.39 209 Very fine sand 4.1" 2.5 b 2.5 b 2.0" 0.63 212 Mull 2.7' 1.5b 1.4" I.l' 0.64 213 Mull 2.0* 1.7"" 1.3* I.l' 0.42 1 Results of each soil were tested separately. Means marked with the same superscript do not differ at P = 0.05. 209 Agric. Sei. Fin!. 2 (1993) the extracts as was described earlier. Added Zn was accurately recovered (Table 3). d. Repeated pyrophosphate extraction The effect ofrepeated pyrophosphate extraction on the quantities of Zn dissolved sequentially with oxalate was studied with two soils (211,213). The 2.5-g soil samples (four replicates) were extracted once, twice or three times with 50-ml aliquots of pyrophosphate, washed with water and extracted once with a 50-ml aliquot of oxalate (pH 2.9). In both soils, the first pyrophosphate treatment ex- tracted more than did the second and the third treat- ment (Table 6). Repeated pyrophosphate extrac- tions tended to reduce the quantities of Zn extracted by oxalate in the mull (213), suggesting that thetwo solutions dissolved Zn to some extent from a com- mon pool. An alternative but less likely explanation is that part of the sample was lost in the successive washings, resulting in a smaller quantity of soil remaining in the oxalate extraction. The number of pyrophosphate extractions did not have a consistent effect on theresults of the oxalate extraction in the mineral soil 211. In soil 211, the quantities of Zn extracted by oxalate were substantially larger than those dissolved with the second and thirdextraction by pyrophosphate. In this soil there was obviously Table 6. Soil Zn extracted with one, two or three sequential treatments by pyrophosphate and a successive extraction by oxalate. I, II and 111 refer to the first, second and third py- rophosphate extraction. 1 Soil Zn (mg kg ') extracted by Zn (mg kg 1) pyrophosphate extracted i n ~W~ bymlale 211 3.5» - - 2.2" 3.6» 0.7' - 2.5» 3.6» 0.8I*-' 1*-' 1.0" 2.1" HSDooj 0.20.1 213 5.1» - 1.6» 4.9s 1.4b - 1.4ab 4.9» 1.4" 0.9 C 1.2b HSD005 0.20.2 1 Results of pyrophosphate and oxalate extractions were tested separately. The two soils were tested separately. Means marked with the same superscript do not differ at P = 0.05. a pool of Zn which was extractable by oxalate but which was resistant even to repeated pyrophos- phate washings. e. Reproducibility and additivity of the results of sequential extractions The reproducibility of the results of pyrophosphate and oxalate extractions was studied with 13 soils (201, 202, 206, 207, 208, 209, 210, 211 and 212 in Appendix 1; 10,73,90and 100 in Appendix 2). The 2.5-g soil samples (two replicates) were extracted in sequence with 50-ml aliquots of0.1 M pyrophos- phate, washed with water and extracted with 50 ml of0.05 M oxalate (pH 2.9). Another two replicates were sequentially extracted and analyzed for Zn a few days later. The results of the first extraction were designated Py 1 and Ox 1, those of the second extraction Py 2 and Ox 2. The differences between Py 1 (5.12 mg kg ') and Py 2 (5.20 mg kg' 1) as well as between Ox 1 (2.15 mg kg' 1 ) and Ox 2 (2.17 mg kg' 1 ) were not statistically significant according to the paired t-test. In the 13 soils, the difference between the two means ofZnpy ranged from -0.65 to 0.38 mg kg" 1 and that of Zn 0\ from -0.30 to 0.25 mg kg' 1 . The coefficient of variation of the four individual determinations in the 13 soils ranged 2.8 - 12.4% (mean 5.3%) and 0.6 -13.4% (mean 4.5%) for ZnPy and Zn ox,0 x, respectively. In sequential fractionation procedures part of the sample may be lost during the numerous decanta- tions. In order to study the importance of this source of error, 2.5-g samples (four replicates) of 13 soils were sequentially extracted by pyrophosphate for 18 hours, washed with water and extracted by ox- alate for 4 hours. After the oxalate extraction, the remaining sample was washed with water, dried and ground, and a 500-mg sample (two replicates) was digested according to the HNO3 - HCIO4 - HF - H2SO4 procedure, and residual Zn (Znres) was measured. Also Zntot (two replicates) was deter- mined. The sums of Znpy , Zn o x and Znres were compared with Zntot (Table 7). In seven soils the sum of fractions was higher(1.1 - 13.6 mg kg' 1 , 2 - 11%) than Zntot, while in six soils the sum of frac- tions was lower (0.1 - 10.5 mg kg' 1 ,0.1 - 10%) than Zntot- The difference between Zntot and the sum of 210 Agric. Sei. Fint. 2 (1993) Table 7. Soil Zn extracted by pyrophosphate (Znpy) and oxalate (Znox) as well as residual Zn (Znres ), and the sum of frac- tions (Znpy + Znox + Zn res) and total Zn (Zn tot) of 13 representative soils. Soil Zn 10 , Znpy Zn01l Zn res Sum of fractions m g kg- 1 mg kg-' %' 201 Heavy clay 137.23.1 2.4145.3 150.8 110 102 Gyttja clay 109.14.2 2.0109.3 115.4 106 202 Silty clay 184.62.7 3.2183.3 189.2 102 206 Very fine sand 109.52.1 2.194.5 99.0 90 207 Very fine sand 140.62.7 2.3137.6 142.6 101 208 Very fine sand 91.1 2.8 2.582.7 88.0 97 209 Very fine sand 88.05.1 2.678.6 86.3 98 210 Silt 151.53.9 3.0150.6 157.5 104 211 Fine sand 67.93.6 2.459.5 65.9 97 73 2 Sandy moraine 15.73.2 1.213.0 17.3 110 212 Mull 88.03.6 1.482.9 87.9 100 902 Carex peat 42.212.3 1.533.2 47.0 111 1002 Carex peat 34.4 17.5 1.716.3 35.5 103 Mean 96.9 5.1 2.291.3 98.6 102 ' Percent of Zn 10, 2 Soil from surface soil material (Appendix 2) the fractions was not statistically significant (t = 0.897ns ', paired t-test), showing that no major loss of the sample had occurred. The sum of the frac- tions correlated closely with Zntot (r = 0.99 ). 2.2 Chemical and statistical analyses 2.2.1 Determination of Zn All the extractions and digestions were performed in duplicate and were repeated when large devi- ations between the replicates occurred. In filtra- tions, Schleicher & Shiill 5893 (Blue ribbon) filter paper was used unless otherwise mentioned. Sili- con and polythene stoppers were used in capping centrifuge glass tubes and volumetric flasks be- cause rubber stoppers were found to be sources of solubleZn. The centrifugations were run for 10min at 3000 G. Zinc concentrations of the MgCh ex- tracts were measured by atomic absorption spectro- photometry (AAS) using the standard addition method. Zinc concentration of the other extracts was measured by AAS using standard solutions matched for the matrix of the extracts. a. Total Zn and chemically specific fractions ofZn in soil Total Zn. A 500-mg soil sample was digested in a teflon crucible with 20 ml of HNO3 until dry. Thereafter 3 ml of HCIO4 and 3 ml of H2SO4 were added and warmed until fumes evolved. Heating was continuedfor 10 minutes. Then, 5 ml ofH2SO4 and 15 ml of HF were added and evaporated to dryness. To remove the fluoride, 5 ml of concen- trated H2SO4 was addedand evaporated to dryness. Finally, 20 ml of deionized water and 10 ml of concentrated HCI solution were added, and the mixture was warmed up and washed into a 100-ml volumetric flask. Water-soluble and exchangeable Zn was extracted by shaking 10g ofsoil for 2 hours with 50 ml of0.5 M MgCl2 in 100-mlpolythene tubes in a reciprocat- ing shaker, centrifuged and filtered. Extraction with o.l' M K4P207 solution (pH 10) was 211 Agric. Sei. Fin!. 2 (1993) performed by shaking 2.5-g samples ofsoil in 50 ml ofpyrophosphate solution in a reciprocating shaker in centrifuge glass tubes. After 1 hour of shaking the suspensions were allowed to stand overnight (16 hours); the following morning the suspensions were shaken for 10 more minutes, centrifuged and filtered. The sample was washed by shaking with 50 ml of deionized water for 1 hour, and after centrifugation the solution was discarded. Oxalate extraction was carried out sequentially after the pyrophosphate extraction. Oxalate solu- tion (50 ml of 0.026 M ammonium oxalate, 0.024 M oxalic acid, pH 2.9) was added into the centri- fuge glass tubes and shaken for 4 hours in daylight, centrifuged, filtered and analyzed for Zn. h. Procedures used in soilfertility testing Contrary to the fractionation of soil Zn, determina- tion of Zn in soil testing does not aim at extracting chemically specific fractions. These determinations do not involve assumptions of the bonding mech- anism or soil constituent to which Zn is bound but attempt to obtain information on the size of Zn reserves available to plants. The solutions should ideally extract Zn from the same soil components which supply plants with Zn, and the quantities of Zn extracted should correlate with Zn uptake by plants. Mineral acids (HCI), neutral salts (1 M MgCb) and chelating agents (EDTA, DTPA) are commonly used for the extraction of Zn in soil testing. In the present study, methods presented in the literature were applied, and studies on the opti- mization of the procedures were not carried out. In the acid ammonium acetate procedure (AAAc), a solution containing 0.5 M CH3COONH4 and 0.5 M CH3COOH was made of acetic acid and NH4OH, and the pH was adjusted to 4.65 with NH4OH or acetic acid. This solution is used in soil testing in Finland to extract Ca, Mg, K and P, and this was also used as an extractant for plant-available Zn by Sillanpää and Lakanen (1966). In the present study, 20 ml of soil was shaken with 200 ml of the extractant in polythene bottles in a planar shakerfor 1 hour, filtered and analyzed for Zn. In the AAAc-EDTA procedure , the soil is extracted with a solution containing 0.5 M CH3COONH4, 0.5 M CH3COOH and 0.02 M Na2-EDTA at pH 4.65 (Lakanen and Erviö 1971). Zinc, together with other metallic micronutrients, has been ex- tracted with this solution in soil testing in Finland since 1986. In this procedure, 25-ml samples of soil were shaken with 250 ml of the extracting solution for 1 hour in a rotary shaker, filtered (Tesorp 04110, 130 g m ) and analyzed for Zn. Most extractions with AAAc-EDTA were performed routinely in duplicate at Viljavuuspalvelu Oy - Soil Analysis Service Ltd. Part of the extractions with AAAc- EDTA were carried out at Kemira Oy Espoo Re- search Centre and at the Department of Applied Chemistry and Microbiology, University of Hel- sinki. For the DTPA procedure, developed by Lindsay and NORVELL (1978) and commonly used as an extractant for metallic micronutrients in soil test- ing, a solution containing 0.005 M diethylenetria- minepentaacetic acid (DTPA), 0.01 M triethanola- mine (TEA) and 0.01 M CaCh at pH 7.3 was prepared. In the extraction, 10 g of mineral soil or 10ml of organogenic soil was shaken for 2 hours in polythene bottles, filtered and analyzed for Zn. c. Zinc in plant material The Zn content of plant material was determined at Soil Analysis Service Ltd. Plant samples were dried at 60°C and ground. Prior to analysis, approxim- ately 1.0 g of plant material was weighed into tared glass vessels and the exact weight was recorded. The sample was dried at 105°C for 4 hours, cooled and weighed, and the dry matter content was calcu- lated. Simultaneously, another sample (approxim- ately 1.0 g, exact weight recorded) was weighed for dry ashing. The sample was heated in a quartz crucible at 550°C for 4 hours until a white ash was obtained. After cooling, the ash was wetted with a few drops of deionized water, 10 ml of 4 M HCI was added, and the crucible was heated for 30 minutes in a sandbath. The contents of the crucible were transferred quantitatively into a 100-ml volu- metric flask which was filled with water. After the 212 Agric. Sei. Finl. 2 (1993) remaining solid material had settled to the bottom, a 10-ml sample was takenand the Zn concentration of the solution was determined by AAS. The con- sistency of the results was checked by including one standard hay sample in every set of 40 samples. In 35 determinations, the mean Zn concentrationof the standard sample was 22.5 mg kg' 1 , range 19-31 mg kg' 1 , standard deviation 2.56 mg kg' 1 and coef- ficient of variation 11.4%.In addition, in one deter- mination the standard gave a value of 42 mg kg' 1, probably due to contamination at some point, re- sulting in repeated determinations of several samples of the set. Routinely, a duplicate deter- mination was carried out with every eight samples. d. Zinc in fertilizers Fertilizer samples were dissolved withaqua regia to facilitate the determination of Zn. A sample (1.00 g) of ground fertilizer was weighed into a 250-ml beaker, and a few drops of water, 10ml of concen- trated HNO3 and 30 ml of concentrated HCI were added and evaporated to dryness. After cooling, 10 ml of concentrated HCI was added and evaporated to dryness. Thereafter, 50 ml of water and 10ml of concentrated HCI were added and boiled until the precipitation was dissolved. The solution was poured into a volumetric flask, filled and filtered if necessary and analyzed for Zn. 2.2.2 Other analyses The soil organic carbon was determined by a modified wet digestion method (Graham 1948). It was assumed that 80% of the carbon was oxi- dized in the treatment. The organic matter content was calculated by multiplying the organic C con- tent by 1.724. The particle size composition of the mineral material in the soil samples was determined by the pipette method (Elonen 1971). The deter- mination was made for all mineral soils (organic matter content less than 20%) and for most mull soils (organic matter content 20 - 40%). Soil pH was measured in water (20 ml of soil, 50 ml of water) after 2 hours of equilibration. The bulk density of ground (<2 mm) soil was determined by weighing two 50-ml samples of soil. Poorly crystalline Fe and A 1 oxides were ex- tracted with 0.05 M oxalate solution at pH 3.3 (Niskanen 1989).The concentrations ofFe and A 1 in the extracts were measured by AAS. The air- acetylene flame and acetylene-nitrous oxide flame were used in the determination of Fe and Al, re- spectively. In order to determine the content of Zntot in textural fractions, clay (<0.002 mm) and silt plus very fine sand (0.002 - 0.05 mm) fractions were separated in three soil samples. The flocculating and cementing agents were first removed with hy- drogen peroxide (H202) and by a treatment with sodium dithionite (Na2S2oa) and sodium citrate using NaHCOs as a pH buffer (pH 7.3) (Olson and Ellis 1982). The actual separation of the textural fractions was carried out by an automated proced- ure for the gravity sedimentation- decantation tech- nique (Rutledge et al. 1967) with the equipment ofTexas A&M University (College Station, Texas, USA). The contents ofK, NH4+-N and NO.V-N in fertil- izers were determined after dissolution of the fertil- izer (20 g) with water (1 dm3). The sum of NH4+-N and NOs'-N was taken as the concentration of total N. For the determination of total P, the fertilizer was dissolved in H2SO4 and HNO3. The pH of the fertilizers was measured in a 10% solution (w/v). The concentration of N in barley grains was measured by the near-infrared (NIR) technique. The vegetative parts were analyzed for N by the Kjeldahl method. 2.2.3 Statistical methods The statistical analyses were mainly carried out according to the procedures presented by Ranta et al. (1991). The variation of the results was studied by calculating the mean deviations, MD = Xlxj-pl/N, or standard deviations, s = V| X(x, - |i) 2 ]/(« -1). In assessing the variation of replicates, the mean de- viations were calculated. Otherwise, standard de- viations were used. Fractiles of 10% (Fio%) and 25% (F25%, quar- tiles) were formed in order to group the material in terms ofvarious characteristics. Occasionally there 213 Agric. Sei. Fint. 2 (1993) were several equal results, all of them placed in the same fractile. Therefore the ultimate sizes of the fractiles may deviate from F25% and Fio%. Means obtainedfrom two populations were stud- ied with the t-test. The effect of a treatment on several soils was studied by the t-test for paired measurements. Analysis of variance was used to test statistically significant differences between several means. The significance of the differences between individual means was tested by Tukey’s test (HSD, P = 0.05). Means marked with the same superscript do not differ at P = 0.05. The correlation between different charac- teristics of a population was studied. Owing to the skewed distribution of the results of several vari- ables, logarithmic transformations (natural loga- rithms, loge) of results were commonly used. In addition to the linear correlation coefficients, Spearman rank correlation coefficients were calcu- lated. The z-transformation test was applied to test the differences between the linear correlation coef- ficients. Regression analyses were carried out in order to study the dependence between variables. Statistic- ally not significant (P = 0.05) independent variables were excluded from theregression equation one by one and the equation was recalculated until all vari- ables in the equation were significant. The signific- ance of the multiple determination of theregression equations was tested by the F-test. The signific- ance of each regression coefficient (b) was tested by the t-test. To depict the relative importance of statistically significant variables, the standard par- tial regression coefficients, or beta coefficients ((3), were calculated as follows (Steel and Torrie 1981): b’ =b ■ si/sy, where si = standard deviation of an independent variable and sy = standard devia- tion of the dependent variable. Statistical significance of various indices is in- % dicated with asterisks. One asterisk ( ) indicates significance at the 5% risk level (P = 0.05), two asterisks ( )at the 1% (P = 0.01) and three aster- isks (***) at the 0.1% level (P = 0.001); n.s. indi- cates no statistical significance (P>0.05). 3 ZINC IN SOIL 3.1 Experimental soils Most laboratory studies and two pot experiments were carried out with soils of a material of 107 samples which were collected from plough layers (Ap horizons) of cultivated fields in differentparts ofFinland. The samples were collected in 1987and 1989 to represent the distribution of soil classes of cultivated soils of Finland as reported by Kurki (1982). The samples were taken from rural areas at least 100 m away from roads and electric wires. Moist soil samples were air-dried at room temperat- ure and stored in plastic bags. Part of the sample was ground to pass a 2-mm sieve and stored in a cardboard box. Mineral soils except moraines were designated according to the textural classification of Juusela and Wäre (1956). Clay refers to the fraction finer than 0.002 mm, silt to 0.002 - 0.02 mm, very fine sand to 0.02 - 0.06 mm and fine sand to 0.06 - 0.2 mm. Mineral soils containing >30% of clay are called clay soils. Occasionally, other min- eral soils are collectively called coarse mineral soils. Organogenic soils (organic matter content >20%) were divided into mull and peat soils, with organic matter contents of 20 - 40 and > 40%, respectively. The soil characteristics are presented in Appendix 2 and summarized in Table 8. The vertical distribution of Zn was studied on seven soil profiles of cultivated fields (Appendix 3). Soil profiles were sampled according to visible horizon boundaries if present. Where the subsoil was apparently homogeneous, the samples were taken to represent 20-cm thick layers. Also 15 pairs of samples taken from the plough layer (Ap hori- zon) and the respective subsoil (30 - 35 cm) (Ap- pendix 4) were investigated. The two samples of the pair were usually of the same soil class. In one case, an organogenic soil had a fine sand subsoil and one case was the contrary. 214 Agric. Sei. Fin!. 2 (1993) Table 8. Distribution of surface soil samples into soil classes, and some chemical and physical properties of the experi- mental soils. Soil class n Organic C Clay pH Fe ox Alox Bulk density 1 % "7o mmol kg" 1 mmol kg" 1 kg dm ' Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Clay 25 3.5 C 1.2-9.5 51 a 32-74 6.0a 4.6-6.8 99a 55-172 79ab 47-172 0.96" 0.76-1.14 Silt, loam, 20 2.5C 0.8-5.3 20" 6-29 5.9a 4.2-6.8 80ab 51-210 59 b 26-137 1.00b 0.77-1.16 very fine sand Fine sand, moraine 28 2.7C 0.7-6.1 6 C 1-16 6.0a 4.9-7.4 51" 10-231 57 b 9-178 1.15» 0.89,1.43 Mull 14 18.9b 12.4-22.6 n.d. - 5.5ab 4.8-6.2 120a 54-249 107a 17-266 0.65 c 0.53-0.77 Peat 20 38.0a 23.9-50.4 n.d. - 5.0" 3.8-6.2 131 a 29-252 91 ab 10-249 0.37" 0.25-0.55 1 Ground (<2 mm) soil n.d. = Not determined 3.2 Zinc in surface soil 3.2.1 Total Zn a. Soil samples Total Zn (Zntot) in the surface soil samples ranged from 10 to 420 mg kg' 1 , mean 71 mg kg’ 1 (Appen- dix 5). In a fine sand soil (soil 71 from Harjavalta) there was a very high content of Zntot (420 mg kg' 1 ), while the bulk of the results ranged rather uniformly between the second highest (202 mg kg' 1 ) and the lowest value (10.3 mg kg' 1 ). The ranges ofZntot overlapped markedly in the five soil classes (Table 9). However, the average Zntot in the clay soils was higher than that ofsilt, loam and very fine sand soils, and excluding soil 71, the Zn tot in fine sands and moraines was still lower. The mean Zntot of the two organogenic soil classes did not differ significantly from one another or from the fine sandand moraine soils but was lower than that of the more fine-textured mineral soil classes. The mean deviation of the individual measurements of a soil sample averaged 1.8 mg kg' 1 , i.e. 2.8% of the mean, range 0 - 17.6% of the mean. The mean deviation exceeded 5% in 18 soils which were poor in Zntot. The results of Zntot were divided into quartiles (F25%) (Table 10). The frequency of the different Table 9. Total Zn in the surface soils. Soil class n Mean s Range mg kg- 1 Clay 25 141.0" 37.0 66.4-202 Silt, loam, 20 96.4 b 34.5 58.0-201 very fine sand Fine sand, moraine 28 62. 1 1 73.1 13.4-420 -soil 71 excluded 27 48.8' 20.9 13.4-102 Mull 14 48.7' 17.9 20.0-80.1 Peat 20 34.7' 20.3 10.3-85.6 1 Mean not included in the statistical analysis. Table 10. Limits of quartiles (F25 %) of Znto, and number of soils from different soil classes in each quartile. Soil Quartile of Zn 101 and its limits class mg kg- 1 I II 111 IV a: 112 109-66.8 66.4-40.3 <39.2 Clay 19 510 Silt, loam, very fine sand 611 3 0 Fine sand, moraine 1611 10 Mull 04 6 4 Peat 016 13 soil classes in each quartile demonstrates the abundance of Zntot in clay soils and the small re- -215 Agric. Sei. Fint. 2 (1993) serves of Zntot in the coarsest mineral soils and organogenic soils. As many as 19 out of 25 clay soils occurred in the largest F25%, six out of the seven heavy clay soils (clay > 60%) containing more than 150 mg Zntot kg' 1. The smallest F25% contained 10 fine sand and moraine soils, and in these soils more than half (57 - 91%) of the mineral material was coarser than 0.06 mm (i.e. fine sand or coarser). However, the peat soils were poorest in Zntot. As many as 13 out of the 20 peat soils oc- curred in the smallest F25%. When the results were transformed into milli- grams per dnv of soil, the differencebetween min- eral and organogenic soils became greater. The average Zntot was 31 and 14 mg dm in mull and peat soils, respectively, while the results of the mineral soils were not altered by the transforma- tion. The present material consisted of 11 Carex peat soils; eight of them contained less than 10 mg 3 3Zntot dm of soil. The lowest Zntot (3.2 mg dm ), occurring in a Carex peat soil of Sotkamo (97), corresponded to 6kg ha' 1 in a 20 cm deep plough layer, while clay soils commonly contained as much as 300 kg Zntot ha' 1. Linear correlation coefficients were calculated between Zntot (mg kg' 1 ) and some soil charac- teristics (Table 11). In mineral soils, excluding soil 71, Zntot correlatedpositively with clay content and negatively with the content of coarse mineral ma- terial (>0.06 mm). There was also a positive cor- relation between Zntot and Fe 0x, but the partial correlation between these two variables was not Table 11. Linear correlation coefficients (r) between Zntot (mg kg ') and some soil properties of mineral and organo- genic soils. Soil characteristic Mineral soils Organogenic soils n = 72 n = 34 pH 0.23" s 0.29 ns Organic C 0.00" s -0.53" Feox 0.40"* 0.03" s Alox 0.24* 0.17" s Clay 0.81*" Silt 0.38" CF 1 -0.79"* 1 CF = Coarse mineral fractions (>0.06 mm). statistically significant when the effect of clay was eliminated. The dependence of Zntot on clay con- tent in mineral soils is presented in Figure 1. Some soils (17, 21, 38, 71) contained more Zntot than the other soils of the same clay content. Inversely, the gyttja clay 12 (Vihti) and the silty clay 13 (Perniö) contained less Zn than expected. In soil 12 the organic C content (9.5%) was higher than average, resulting in a smaller quantity of mineral material and lower Zntot in the sample weighed for the analysis. The low Zntot of soil 13 may be due to the abundance of coarser materials which are usually poor in Zntot- In soil 13, 33% of the mineral material was coarser than 0.02 mm (very fine sand and coarser), while the average of these materials in clay soils was only 20%. In organogenic soils, there was a negative cor- relation between Zntot and organic C. The content of mineral material is inversely reflected in the organic C content and the correlationbetween Zntot and organic C thus indicates the fact that mineral material was richer in Zntot than was organic mat- ter. Figure 2 shows that all the soils which con- tained more than 35% organic C exhibited a very low concentration of Zntot- The results of Zntot were further studied by mul- tiple regression analyses. In mineral soils Zntot (mg kg' 1 ) increased with increasing content ofclay and silt (%) and Al ox (mmol kg' 1). According to the regression analysis, an increase in organic C (C, %) Fig. 1. Dependence of total Zn (ZniW ) concentration of min- eral soils on clay content. 216 Agnc. Sei. Finl. 2 (1993) was coincident with the decrease in Zntot even though there was no significant linear correlation between these two variables. The t-test of the re- gression coefficients and beta coefficients C|3) of the independent variables showed that clay content was by far the dominantvariable (Table 12). The regres- sion equation was as follows (n = 72): Zn,ot = 1.79 Clay + 0.66 Silt - 7.90 C + 0.20 Alox + 42.14 9 *** R 2 = 0.74 In organogenic soils, the dependence ofZntot on different soil characteristics was weaker. In no -2equation did the coefficient of determination (R ) exceed 0.30 when the results were expressed as milligrams or millimoles per kilogram of soil. However, when theregression analysis was carried out withresults transformed into milligrams ormil- limoies per dm of soil, a higher coefficient of 2multiple determination (R ) was obtained. Accord- ing to the following equation (n = 34), Zntot (mg dm'3 ) decreased with increasing organic C (%) -Jwhile Alox (mmol dm ) had a positive impact on Zntot: Zntot = -0.69 C + 0.11 Alox + 36.75 o *** R 2 = 0.60 Table 12. t-Values of the regression coefficients and beta coef- ficients (P) of the independent variables explaining the vari- ation of Zn tot in mineral and organogenic soils. Independent Mineral soils Organogenic soils variable t p t p Clay 11.469*" 0.77 Silt 3.224" 0.21 Organic C -3.576"* -0.25 -4.719*" -0.58 Alox 2.056* 0.14 2.635* 0.33 The organic C content, being relatively the more important variable (Table 12), inversely reflects the abundance of mineral material in the soil, and Alox may stand for the abundance of aluminosilicates. There was a negative correlation between organic C and Alox (r = 0.48 ), showing that the Alox de- creased with decreasing mineral material, which obviously also resulted in a decrease of Zn tot. b. Particle sizefractions Of three silty clay soils (204 and 205 of Appendix 1; 10 of Appendix 2), clay and silt plus very fine sand were separated and analyzed for Zntot- The textural fractions separated had probably lost at least part of the secondary Zn during the pretreat- ments with hydrogen peroxide, citrate and dithionite. Therefore, the Zntot of the soil fractions actually gives the quantity of Zn contained in prim- ary minerals, while the results of the whole soil containedprimary and secondary Zn. The clay frac- tion contained more Zntot than did silt plus very fine sand (Table 13). In soil 205, the clay fraction was slightly poorer in Zntot than in soil 204, while the Table 13. Content of Zn lm (mg kg 1) in clay and silt plus very fine sand fractions and in the whole soil in three soils. 1 Fraction Soil 10 204 205 Clay 189.3ab 199.5» 178.8" Silt plus very fine sand 83.0" 69.8 e 60.2C Whole soil 112.b 99.7' 85.4" HSD005 12.8 1 All means were tested simultaneously. Fig. 2. Dependence of total Zn (Zntot) concentration of or- ganogenic soils on the organic C content (C). 217 Agric. Sei. Fin!. 2 (1993) silt plus very fine sand of soil 10was richer in Zntot than this fraction in the other two soils. The results of these analyses confirmed that the clay content largely determines the concentration of Zntot in a mineral soil but also silt and very fine sand seem to contribute substantially to Zntot. 3.2.2 Fractions of soil Zn In the fractionation of soil Zn, water-soluble and exchangeable Zn (Znex ) were extracted by MgCI;;. A new sample was weighed for the sequential ex- traction with pyrophosphate and oxalate which were assumed to dissolve Zn bound by organic matter (Znpy) and sesquioxides (Zn„x ), respect- ively. Residual Zn (Znres) remaining in the soil after the oxalate extraction was obtained as the differ- ence ofZntot and Znpy + Znox. a. Water-soluble and exchangeable Zn Water-soluble and exchangeable Zn (Znex ) ranged from 0.3 to 22.0 mg kg’ 1 (Appendix 5). The mean Zn ex (Table 14) did not differ markedly from one mineral soil class to another, but the means in the two organogenic soil classes were considerably higher than those of the mineral soil classes. When studying the results expressed as milligrams ofZn per dm3 of soil, the difference between the means of the five soil classes were not statistically signi- ficant. Table 14.Water-soluble and exchangeableZn in surface soils. n Mean s RangeSoil class mg kg ' Clay 25 I.7 b 1.2 0.5-4 9 Silt, loam, 20 1.3» 0.8 0.5-3 5 very fine sand Fine sand, moraine 28 2.5 1 4.3 0.3-22 0 - soil 71 excluded 27 1.8» 1.9 0.3-8 3 Mull 14 2.6» 2.0 0.9-7.0 Peat 20 5.2“ 2.9 1.1-11.0 1 Mean not included in the statistical analysis. b. Zinc bound by organic matter and sesquioxides In 106 soils, Zn extracted with pyrophosphate (Znpy) ranged from 1.4to 53.8 mg kg" 1 . In addition, in soil 71 rich in Zntot there was also plenty of Znpy (227 mg kg' 1) (Appendix 5). The mean Znpy was higher in peat soils than in the other four soil classes (Table 15). However, after transforming the results to milligrams per dm of soil, statistical differences between the soil classes were nonexistent with means of 4.9 and 5.3 mg dm in the mull and peat soils, respectively. Soil Zn extracted by oxalate (Zn ox) sequentially after the pyrophosphate treatment ranged in 106 soils from 0.5 to 13.0 mg kg' 1 , while soil 71 con- tained 115 mg Znox kg’ 1 (Appendix 5). The mean Znox (Table 15) was higher in clay soils than in fine sand and moraine soils or in organogenic soils. When expressing theresults as milligrams ofZn per dm ofsoil, the organogenic soil classes were by far poorer in Znox than were the mineral soils with means of 1.2and 0.9 mg dm in mulland peat soils, respectively. In nine out of the 25 clay soils, Zn ox was higher than Znpy . In soils other than clay, Zn ox was lower than Znpy with only two exceptions; in organogenic soils Znpy was four to five times higher than Znox . The average mean deviation of the replicates of Znpy was 0.33 mg kg' 1 , or 5.5% of the mean and ranged from 0 to 18.9% of the mean in the 107 surface soils. The mean deviation ofZnox averaged 0.16 mg kg’ 1 , or 4.8% of the mean, ranging from 0 to 25.2%. The mean deviationexceeded 10% in 15 and eight soils in the determination of Znpy and Znox , respectively. The lowest results of Znpy (Fn%) were distrib- uted over all mineral soil classes, while those of Znox (Fio%) occurred in fine sandand moraine soils (eight soils) as well as in organogenic soils (three soils). There was no soil in common to the smallest Fn% of Znpy and the smallest Fio% of Zn ox . The mineral soils poorest in Znox were characterized by a coarse texture and low Feox content. In the eight fine sand and moraine soils of the smallest Fio% of Znox the average concentration of Fe ox was 22.0 mmol kg' 1 which was less (t = 3.598 ) than in the rest of the fine sand and moraine soils (mean 62.3 218 Agric. Sd. Fint. 2 (1993) Table 15. Soil Zn extracted sequentially by pyrophosphate (Znpy ) and oxalate (Znox) as well as residual Zn (Zn,,,,). 1 Soil class n Znpy , mg kg-' Zn ox , mg kg- 1 Zn res , mg kg ' Mean Range Mean Range Mean Range Clay 25 4.9b 1.4-23.1 3.5" 1.2-13.0 132.0" 62.6-193 Silt, loam, very 20 3.4" 1.4-6.7 2.5»» 1.4-5.0 90.5b 54.2-192 fine sand Fine sand, moraine 28 12.72 1.4-227 6.1 2 0.6-115 43. 3 2 10.2-96.9 -soil 71 excluded 27 4.8" 1.4-23.9 2.0" 0.6-8.8 42.CK 10.2-96.9 Mull 14 7.8" 1.6-26.9 1.8" 1.0-3.5 39. 1"1 15.7-69.8 Peat 20 14.1» 2.2-53.8 2.4 ab 0.5-10.3 18.7" 3.9-53.0 1 Results were tested separately for Znpy and Znox . 2 Mean not included in the statistical analysis. Table 16. Complexed Zn calculated as the difference between Znpy and Zncx (i.e. Znpy-Zn ex). Soil class n Mean s Range (Znpy -Zn„)/Znpy mg kg-' % Clay 25 3.1" 3.4 0.5-18.2 43-84 Silt, loam, very fine sand 20 2.2» 1.6 0.6-4.8 16-85 Fine sand, moraine 28 10.2 1 38.3 0.6-205 22-90 - soil 71 excluded 27 3.0 b 3.5 0.6-18.7 22-85 Mull 14 5.1»" 4.8 0.3-6.1 19-78 Peat 20 8.9» 9.8 0.7-43.0 19-80 1 Mean not included in the statistical analysis. mmol kg 1, n = 20). The highest results (Fio%) of Zn Py occurred with three exceptions in organogenic soils, while those of Zn Gx (Fio%) were the most common in clay soils. c. Complexed Zn Water-solubleand exchangeable Zn extracted with MgCh was probably included also in Zn extracted by pyrophosphate (Znpy ). Therefore the results of the pyrophosphate extraction can be divided into two parts: (1) water-soluble and exchangeable Zn bound by non-specific electrostatic forces and (2) Zn presumably bound mainly by organic matter in complexed forms by covalent forces. The quantities of complexed Zn were calculated as the difference of Znpy and Zn ex (i.e. Znpy - Zne x) (Table 16). This fraction was larger in peat soils than in the mineral soil classes but, again, there were no differences between the soil classes when the results were ex- -3pressed as milligrams of Zn per dm . The percentage of Znpy which was bound by covalent forces, i.e. the ratio 100 • (Znpy - Zitex)/Znpy , ranged 14- 90% (Table 16) and correlated with soil pH (r - 0.65* ). The fractile (Fio%) of the smallest percentage (14 - 38%) ofZnpy in complexed forms consisted ofsix organogenic soils (pH 3.8 - 5.6) and of five coarse mineral soils (pH 4.2 - 5.8). The four fine sandand moraine soils of this group had only a moderate acidity (pH 4.9 - 5.8) and a very low content of clay (<4%) as well as Fe ox and Alox. Three of these soils (72, 73, 74) were those of the coarsest texture in the whole soil material. For com- parison, the most acid clay soils (10, 20, 26) had nearly the same pH (4.6, 5.2, 5.0, respectively) but a higher percentage (52 - 62%) of Znpy was not water soluble or exchangeable, indicating a differ- ence in bonding of Zn in acid clay soils and acid fine sands. 219 Agric. Sei. Fint. 2 (1993) d. Residual Zn Residual Zn (Znre s) (Table 15) represents the fraction bound in the mineral lattices. This fraction was the largest in clay soils and decreased in mineral soils with decreasing clay content; 11 soils richest in clay were also in the largest F25% of Znres. The lowest results occurred in or- ganogenic soils; 15 out of 20 peat soils, espe- cially those of the highest organic C content, and five out of 14 mull soils were in the smallest F25% of Znres- The smallest P25% also contained seven fine sand and moraine soils which were very coarse in texture, containing only 1 -7% clay and 3 - 13% silt. The pH of these seven soils (4.9 - 6.3, mean 5.5) was lower (t = 3.295 ) than in therest of the fine sand and moraine soils (mean 6.2). When the results of Znre s were transformed into milli- grams per dm of soil, the difference between or- ganogenic and mineral soils became greater with '1 means of 25.4 and 8.0 mg dm' for mull and peat soils, respectively, while the transformationdid not have a marked influence on the results of mineral soils. e. Relationship between Zn fractions and other soil properties Owing to the skewed distribution of the results of secondary Znfractions (Znex , Znpy , Znpy - Ziiex and Znox), the linear correlation coefficients were cal- culated using the natural logarithms (loge) of the results (Table 17). In order to eliminate the effect of the skewness of the material, also the Spearman rank correlation coefficients were calculated be- tween the various Zn fractions and soil properties. The two correlation coefficients were similar and only the linear ones are presented. Soil 71, ex- tremely rich in Zn, was not included in the calcula- tions. In mineral and organogenic soils, Znex correlated negatively with soil pH. The correlation was made weaker by a few soils which in spite of a pH above 6.5 containedplenty ofZn e x- Znex correlated closely with Znpy, but it should be taken into account that Znex is actually a part ofZnpy ; thecorrelationbetween Znex and complexed Zn (Znpy - Zn ex) remained lower than that between Zn ex and Znpy . Organic C content seemed to correlate with Zn ex , reflecting the lower Table 17. Linear correlation coefficients between Zn fractions and some other soil properties. Tabulations were carried out using natural logarithms of concentrations of Zn, Fe and Al, expressed as mg kg- 1 (Zn) or mmol kg l (Fe, Al). Zn„ Znpy -Zn„ Znpy Zn ox Zn res Mineral soils (n = 72): Clay 0.05" s 0.07" s 0.03" s o.47*** 0.76"* Organic C 0.30" 0.10"» 0.23" s -0.13" s -0.04" s pH -o.7o*** 0.11"» -0.29* 0.28* 0.23" s Feox 0.09" s 0.07" s ' 0.12" s 0.57*" 0.64*" Alox 0.03" s - 0.26* 0.14" s 0.26* 0.38" Zntol -0.02"*- 0.23" s 0.12" s 0.76*" 0.99*" Zn„ s -0.10"s 0.16" s 0.04" s 0.69*" Znox 0.22" s - o.6l*** 0.53*" Znpy 0.78*" 0.87*" Znpy -Zn„ 0.40"* Organogenic soils (n = 34): Organic C 0.48" 0.22" s 0.34* 0.11" 5 -0.80*" pH -0.54"* 0.07"-*- -0.14°» 0.04"» 0.39* Fe ox 0.02" s 0.11" 5 0.08"' 0.03" s 0.22" s Alox -0.20"s -0.34" s -0.33* -0.15" s 0.33 ns Zn,OI 0.13" s 0.36* 0.33" s 0.48" 0.79"* Znres -0.28"s - -0.07" s -0.15" s - -0.05" s Znox 0.50" o.6B*** 0.69*" Znpy 0.85*" 0.95*" Znpy -Znex o.6s*** 220 Agric. Sei. Fint. 2 (1993) pH in soils rich in organic C(r = -0.45 and -0.44 in mineral and organogenic soils, respect- ively). Soils rich in Znpy tended also to be rich in Zn ox- Znox and Znres correlated closely with Zntot in mineral soils but more weakly (z = 2.219 and 12.642 for ZnGx and Znre s, respectively) in or- ganogenic soils. In mineral soils Znox correlated with clay, Feo x and Znre s- Contrary to mineral soils, Znox did not correlate with Znres or Feox in organo- genic soils but there was a significant negative correlation between Znre s and organic C. The relationships between Zn ex and other frac- tions of secondary Zn were further studied by re- gression analyses using the natural logarithms of Zn concentrations. Both in mineral and organo- genic soils Znex (mg kg' 1 ) increased with increas- ing Znpy (mg kg 1 ) and/or decreasing soil pH. Even though there was a statistically significant linear correlation between Znex and ZnQx in organogenic soils, ZnQ x remained insignificant in theregression analysis, owing to the positive correlation between Zn 0x and Znpy. The t-values and the beta coeffi- cients (Table 18) show that pH and Znpy were relatively of equal importance in explaining the variation of Zn e x- The regression equations were as follows: Mineral soils (n = 72): loge Zriex = -0.66 pH + 0.73 loge Znpy + 3.21 O *** R 2 = 0.85 Organogenic soils (n = 34): loge Znex = -0.54 pH + 0.66 loge Zn Py +1.13 R 2 = 0.84 Dependence of Znpy , Znpy - Zn ex and Zn Q x on soil characteristics was studied by regression ana- lyses. The regression equations consisting of Zntot, organic C, pH, Fe0 x, Alo x and in mineral soils clay content explained less than 10% of the variationof Znpy and Znpy - Znex. Instead, a considerable part of the variation ofZnox (mg dm" ) was explained by Zntot (mg dm (n = 106): loge Zriox = 0.65 loge Zntot - 2.00 9 *** R =0.71 /. Distribution ofsoil Zn into differentfractions The distribution of soil Zn into different fractions, expressed as percentages of Zntot, was studied (Table 19). In clay and silt soils the residual fraction (Znres) commonly accounted for more than 90% of Zntot- The distribution of Zn in the mineral soil classes did not differsignificantly from one class to another even though in a few coarse mineral soils a larger part of Zn was in the secondary fractions Table 18. t-Values of the regression coefficients and beta coef- ficients (3) of the independent variables explaining the vari- ation of log Zn„ in mineral and organogenic soils. Independent Mineral soils Organogenic soils variable ~ ~ t P t P pH -10.550*" -0.52 -6.826*" -0.51 log Znpy 12.822*" 0.63 8.995*" 0.67 Table 19. Distribution of soil Zn (%) into different fractions expressed as percentages of Zn tot .> Soil class Zn„ Znpy-Zn„ Znox Zn r„ Mean Range Mean Range Mean Range Mean Range Clay 1.3" 0.3-3.6 2.2' 0.5-9.6 2.5b 1.4-6.8 94.0" 81.0-97.2 Silt, loam, very fine sand 1.5" 0.3-5.5 2.3»» 0.6-4.9 2.6 b 1.5-4.3 93.6» 87.6-97.3 Fine sand, moraine 4.7 2 0.4-27.0 7.5 2 1.4-48.8 4.8 2 2.0-27.4 83.02 18.6-95.2 -soil 71 excluded 4.8" 0.4-27.0 6.0»" 1.4-23.9 4.1» 2.0-11.3 85.1» b 50.5-95.2 Mull 5.7" 2.2-17.9 10.4" 0.7-26.3 3.9b 1.9-7.1 80.0b 59.7-94.0 Peat 17.7» 2.6-37.4 25.1» 2.5-54.5 8.0» 2.8-12.0 49.2C 12.2-84.0 1 Each fraction was tested separately. 2 Mean not included in the statistical analysis. 221 Agric. Sei. Fin!. 2 (1993) (Zriex, Zripy - Zn e x, Zn 0 x) than in the rest of the mineral soils. In mull soils the percentage of Znre s was significantly smaller than in the two most fine- textured mineral soil classes. In peat soils the per- centages of the secondary fractions were substan- tially greater and Znres smaller than in the other soil classes. In the 13 soils richest in organic C (34 - 50%) the sum Znpy + Zn o x corresponded to as much as 68 - 88% of Zniot- In mineral soils, the ratio (Znpy + Znox)/Zntot which reflects the relative abundance of secondary fractions did not correlate with soil properties, but in organogenic soils there was a close correlation between this ratio and or- ganic C (r= o.Bl***). Fractions of Zn were studied separately in min- eral and organogenic soils in which Znpy exceeded 10 mg kg" (mineral soils) or 20 mg kg" (organo- genic soils) (Table 20). In these soils, the secondary Zn fractions ranged from 19% in clay soil 17 to 88% in peat soil 102 and were relatively larger than those in the respective soil class on average. Inquir- ies concerning the farming operations revealed that large quantities of farm-yard manure had been spread to the fields from where soils 53,70, 85 and 95 originated (V. Haataja, P. Luoma and J. Niemi- nen 1991,Kemira Oy, I. Kallioniemi 1991,Suomen Säästöpankki, Pori, pers. commun.). It is likely that the abundance of secondary Zn also in soil 17 can be attributed to the use of farm-yard manure, be- cause the respective field was located at Viikki 0.2 km from the barn of the farm of the University of Helsinki. Soil 71 of Harjavalta had been taken about 2 km from the smelter of Outokumpu Oy. No slag or farm-yard manure had been transported to the field for several years (I. Kallioniemi 1991, Suomen Säästöpankki, Pori, pers. commun.), sug- Table 20. Soil Znpy and Zn ox as well as the ratio (%) between secondary and Zn tol , i.e. 100 • (Zn py + Zn ox)/Zntot , in soils exceptionally rich in Znpy . gesting that the abundance of Zn was airborne. Information of the farming of soils 74, 101 and 102 was not available. 3.2.3 Zinc extracted by AAAc-EDTA In soil testing in Finland plant-available Zn is ex- tracted by AAAc-EDTA at pH 4.65. Therefore, this method was applied also to the present surface soil material, and relationships between Zn extracted by AAAc-EDTA (ZnAc) and chemically more specific fractions of soil Zn were investigated. Soil ZnAc ranged from 0.6 to 165 mg dm' (Appendix 5). The highest result occurred for the same fine sand soil (71) which was rich in Zn according to all indices determined. The second highest result was 29.9 mg dm' and the median of the whole material was 2.9 mg dm . The means of ZnAc did not differ statistic- ally significantly from one soil class to another (Table 21). The mean deviation of the replicates averaged 0.25 mg dm' , or4.4% of the mean, range 0 - 20.8%. Soil 71 excluded, the mean deviation averaged 0.15 mg dm'3 . ZnAc corresponded on av- erage to 45% (range 18 - 76%) and 75% (range 43 - 200%) of the sum Znpy + Zn 0x (mg dm'3 ) in mineral and organogenic soils, respectively. The 15 soils (Fi4%) poorest in ZnAc 1.5 mg dm’3 ) consisted oftwo clay soils, 10coarse mineral soils and three organogenic soils. The pH of the 12 mineral soilsof this group was 5.4 - 6.9, and in nine of these soils, the pH was above or equal to 6.0, which was the mean pH for mineral soils. There Table 21. Soil Zn extracted by AAAc-EDTA from surface soils. Soil class n Mean s Range mg dm' Clay 25 3.73.2 1.1-18.0 Silt, loam, very 20 2.61.5 0.8-5.7 fine sand Fine sand, moraine 28 9.930.9 0.9-165 -soil 71 excluded 27 4.15.8 0.9-29.9 Mull 14 4.03.2 0.8-14.0 Peat 20 4.64.0 0.6-19.4 Soil Znpy Zn OK (Znpy + Zn ox)/ZntoI mg kg- 1 mg kg- 1 % 17, 53, 70, 74 18.37.1 36 71 227 115 81 85, 95, 101, 102 33.85.0 70 222 Agric. Sei. Fin!. 2 (1993) was thus a slight tendency of the soils poor in ZnAc to have a pH higher than average. There were, however, several soils ofhigh pH which contained plenty of ZnAc- Linear correlation coefficients were calculated between ZnAc and other indices of soil Zn using the natural logarithms of the results (mg dm"3 ). The ZnAc correlated most closely with Znpy (r = 0.87 *** rJ and 0.95 in mineral and organogenic soils, re- spectively). The correlation was statistically highly *** *** significant also with Znex (r = 0.76 and 0.79 ) and Zn o x (r = 0.61 and 0.60 ). In the organo- genic soils there was a significant correlation also * between ZnAc and Zntot (r = 0.42 ). Like Zn py , ZnAc did not correlate with soil pH or with the content of clay or organic matter. Despite the highly significant correlation of ZnAc both with Znpy and ZnQx, Znpy (mg dm"3 ) alone explained statistically significantly the variation of ZnAc (mg adm" )in theregression analysis, and ZnQx was not a significant variable. The equation was as follows (n = 106): loge ZnAc = 0.89 loge Znpy - 0.090 R 2 = 0.80 When the regression analyses were tabulated separately for mineral and organogenic soils, slightly different equations were obtained for the two soil groups. In organogenic soils, Znpy alone explained 89% of the variation of ZnAc (equation not shown); other soil characteristics were not sig- nificant. In the equation for mineral soils (n = 72), the contents (%) of clay and organic C were also significant variables, while Znpy (mg dm"3 ) was relatively the most important: loge ZnAc = 0.91 loge Znpy + 0.0064 Clay -0.049 C-0.19 R 2 = o.Bl*** t P logeZnpy 16.642** 0.89 Clay 3.860**' 0.21 Organic C -2.106* -0.12 The above equation shows that at a given level of Znpy, increasing clay content enhanced the extrac- tion power of AAAc-EDTA. The negative regres- sion coefficient of C suggests that, at a given Znpy level, increasing organic C reduced the extraction power of AAAc-EDTA in relation to that of pyro- phosphate. -1Also the relationships between ZnAc (mg dm" ) and Zn ex (mg dm" ) were studied by multiple re- gression analyses. According to the beta coeffi- cients (P) (Table 22), Znex was relatively the most important variable explaining the variationof ZnAc both in mineral and organogenic soils. The equation below shows that the relative efficiency ofAAAc- EDTA to extract Zn increased with increasing soil pH. In mineral soils, also the clay content increased the efficiency of AAAc-EDTA as an extractant for soil Zn as compared to MgCla. The equations were as follows: Mineral soils (n = 72): loge ZnAc = 0.98 loge Ztlex + 0.62 pH + 0.0041 Clay - 3.03 0 *** R 2 = 0.78 Organogenic soils (n = 34): loge ZnAc = 1.05 loge Zllex + 0.48 pH -1.69 o *** R 2 = 0.76 Table 22. t-Values of the regression coefficients and beta coef- ficients (3) of the independentvariables explaining the varia- tion of log ZnAc in mineral and organogenic soils. Independent Mineral soils Organogenic soils variable ~ ~~ t P t p log Zn„ 15.235"' 1.119.779- 0.93 pH 7.586"- 0.56 4.149'" 0.39 Clay 2.402" 0.14 3.3 Vertical distribution of soil Zn Plant roots penetrate farbelow the plough layer and therefore Zn reserves also deeper in the soil may be important in providing the plant with Zn. There- fore, the vertical distribution of Zn was studied by 223 Agric. Sei. Finl. 2 (1993) Table 23. Total Zn (Zntot ) and Zn extracted by AAAc-EDTA (ZnAc) in samples taken from various depths in seven soil profiles. l Depth Zn tO , ZnAc Depth Zn,ot ZnAc cm mg kg- 1 mg dnr 3 cm mg kg-' mg dnr 3 Profile 1: loam/clay loam Profile 2: silt 0-30 82.3 d 2.3b 0-27 93.9» 1.9» 32-38 88.2" 0.7» 30-40 62.9" 0.3' 38-46 97.4 d 0.7' 40-50 68.7" 0.4' 50-60 116.8' 1.3d 50-70 71.9b 0.6' 65-80 132.2»' 1.9' 70-90 43.7' 0.3' 85-100 146.5" 2.0b' 90-100 71.7" 0.6' 105-120 165.9» 5.0» 110-120 96.8» 1.5" HSD00i 19.00.4 HSD005 11.00.4 Profile 3: silty clay/heavy clay Profile 4: fine sand 0-30 129.0 d 4.3» 0-30 22.6b 6.7» 30-40 129.1" 2.4' 30-40 9.2' 0.8" 40-60 137.6' 1.2d 40-45 11.7d' 0.7» 60-80 159.0» 3.3" 45-60 13.7«* 0.3 1" 80-100 191.9» 3.5b 60-80 17.3b'd 0.2' 100-120 192.6» 3.8»b 80-110 20.1"' 0.2' HSD005 6.30.7 110-120 30.5» 0.2' HSD00! 7.20.5 Profile 5: Carex peat Profile 6: Carex peat/mud/heavy clay 0-20 42.3» 0.9» 0-25 65.2' 2.7» 20-30 6.1' 0.6» 30-40 41. 8 d 1.6' 30-40 6.6' 0.9» 40-45 90.3" 6.3' 40-60 5.& 0.4» 50-70 191.8» 2.4» 60-80 8.3' 0.5» 70-80 199.4» 2.7" 80-100 9.9' 0.5» HSD0I)! 23.40.7 100-120 34.3" 1.0» 120-130 29.6 b 1.1» HSD00i 5.20.7 Profile 7: Carex peat/fine sand o—3o 13.0» 6.7» 30—50 6.4" 1.7b 50—70 2.4b 1.5" 70—90 2.9 b 0.7b 90—110 3.5b 0.8b 110—125 14.3» 0.8b HSD005 5.91.8 1 Each profile was tested separately for Zn tol and ZnAc . investigating soil profiles as well as sample pairs consisting of a sample from the plough layer and the subsoil. 3.3.1 Total Zn The seven profiles differed greatly in the content of total Zn (Zntot) (Table 23). In profiles PI, P 3 and P6, where the entire profile or a part of it consisted of clay soil, the peak Zntot exceeded 150 mg kg 1. In turn, in profile P 4 dominated by fine sand as well as in the Carex peat profiles P 5 and P7, all layers contained less than 50 mg Zntot kg’ 1 , most layers even less than 10mg kg" 1 . The Zntot of organogenic layers was dependent on the Zntot of the mineral subsoil. This was demonstrated in profile P 7 which had a Carex peat topsoil very poor in Zntot and a 224 Agric. Sei. Finl. 2 (1993) fine sand subsoil which also was poor in Zntot. On the contrary, in profile P 6 the soil below the or- ganogenic surface horizons was heavy clay rich in Zntot, and also the surface horizons were richer in Zntot as compared with the other two organogenic soil profiles. The content of Zntot showed marked changes in relation to the depth within each soil profile. The highest Zntot occurred either in the plough layer or m the deepest horizon sampled. The lowest /.nun occurred between these horizons, with the excep- tion of profile PI (silty clay) and P 3 (silt) where it was in the two or three uppermost horizons sampled. In the other five profiles (P2, P4, P5, P6, P7) Zntot was markedly higher in the plough layer than in the next layer below. In all profiles but one (P5) was the content of Zntot in the bottom of the profile at least as high as that in the plough layer. Mineral soil had obviously been mixed in the plough layer of Carex peat profile P5, increasing the Zntot in the plough layer of this profile. An evid- ence of the external source of the mineral matter was the presence ofclay (9%). Moreover, the uppermost layer contained only 9% organic C, while in the layer below there was as much as 52% oforganic C. The Zntot of the mineral soil profiles PI, P 2 and P 3 correlated closely with the clay content (r = 0.89** - o.99***); in profile P4, Zntot correlated (r = 0.81 ) with very fine sand which was the finest textural fraction present in abundance. In the or- ganogenic profiles P 5 and P7, Zntot correlated ** negatively with organic C, r = -0.92 and r = - 0.77ns ', respectively. former soil surface currently covered by organic materials. In the three mineral soil profiles (PI, P2 and P3) dominatedby clay or silt there was a tend- ency that deeper in the soil profile ZnAc first de- creased, increasing again in the deepest horizons. In profile PI, ZnAc was highest in the deepest layer sampled. On the contrary, in the coarse mineral soil profile (P4) and in the two Carex peat profiles there was no increase of ZnAc in the deeper layers. In 14 out of the 15 plough layer and subsoil sample pairs, the subsoil was poorer in ZnAc than was therespective plough layer (Table 24, details in Appendix 4). According to the t-test for paired measurements, the difference in ZnAc between the plough layer and subsoil was highly significant (t = 4.804***, n = 15). The only exception was the sample pair from Forssa which consisted ofa mull plough layer and a subsoil of heavy clay which was richer in ZnAc- In the other sample pairs, ZnAc in the subsoil averaged 39% of that in the plough layer. Only in heavy clay subsoils did ZnAc exceed 2.0 mg dm'3 . Table 24. Soil Zn extracted by AAAc-EDTA (Zn Ac ) from the plough layer and subsoil samples. Soil class 1 n ZnAc , mg dm ' Plough layer Subsoil Clay soils 6 4.42.0 Coarse mineral soils 4 2.40.7 Organogenic soils 5 3.0 (3.0)2 1.2 (0.6) 2 1 Soil class of the plough layer. 2 Results of the sample pair of Forssa not included. 3.3.2 Zinc extracted by AAAc-EDTA Within a soil profile, the sampled layers differed markedly from one another in termsof Zn extracted by AAAc-EDTA (ZnAc, Table 23). In all profiles except P 5 and P 6 was the content ofZnAc higher in the plough layer than in the next few underlying ones. In the Carex peat profile P5, all the horizons were equally poor in ZnAc- In profile P6, consisting of an organogenic surface horizon and a heavy clay subsoil, the maximum ZnAc was measured in the upper part of the mineral subsoil which is the 3.4 Extractability of Zn added to soil The ability of common extractants to dissolve Zn from soil was studied on four surface soils (18, 34, 78, 104). Deionized water or ZnSOa solution was added to weighed portions of air-dry soil (three replicates, 200 ml each), and the samples were incubated at an approximate field capacity for two weeks after which the samples were air-dried and ground with a porcelain mortar and a pestle. The soil samples of the first incubation (Zn addition 225 Agric. Sei. Fin!. 2 (1993) 39.06 mg dm ) were extracted (two replicates) with the following solutions: 1.0.5 MMgCla 2. 0.5 M ammonium acetate - 0.5 M acetic acid at pH 4.65 (AAAc) 3.0.5 M ammonium acetate - 0.5 M acetic acid - 0.02 M Na2-EDTA at pH 4.65 (AAAc- EDTA) 4. DTPA - TEA - CaCh at pH 7.3 (DTPA) The unbuffered MgCl2 solution extracted ex- changeable Zn (Zn e\) at soil pH, AAAc at a con- stantpH of4.65. The results of AAAc-EDTA dem- onstrate the effect of the addition of a chelating agent. The use of DTPA allows comparison to be made with an extractant containing the other widely used chelating agent. The primary purpose of the second incubation experiment (Zn addition 9.26 mg dm ) was to study the extractability of added Zn in sequential extraction by 0.1 M K4P207 and 0.05 M oxalate. In both experiments, the results of extractions for which the samples were weighed (MgCb, DTPA, pyrophosphate and oxalate) were transformed to milligrams per dm3 of soil by multiplying the re- sults by the bulk density determined for the incub- ated soil samples. As far as native Zn is concerned, MgCb was the weakest extractant in clay (18) which was the least acid (pH 6.2) of the four soils, while in the three more acid soils MgCl2 and AAAc extracted equal quantities of native Zn (Table 25). In the clay soil, the higher efficiency ofAAAc was probably due to its pH (4.65) which is 1.5 units below the soil pH. The acidity may have caused dissolution of Zn reserves which would not be exchangeable at native soil pH. From the other three soils AAAc probably extracted only the exchangeable Zn fraction. Addition of EDTA to the AAAc solution mark- edly enhanced the extraction of native Zn. In clay (18) and organogenic soils (78, 104) the quantities dissolved were at least tripled, and in the highly acid loam (34) they increased by 50%. DTPA was a weaker extractant than AAAc-EDTA in the three soils except the peat (104) where DTPA and AAAc-EDTA extracted native Zn with an equal efficiency. The sequence of efficiency in mineral soils was thus: MgCb < AAAc = DTPA < AAAc-EDTA In organogenic soils the sequence was as fol- lows: MgCli = AAAc < DTPA < AAAc-EDTA Table 25. Soil Zn (mg dm 3 ) extracted by MgCl2 (Znex), AAAc (ZnAAAc ), AAAc-EDTA (Zn Ac) and DTPA (ZnDTPA ) from soil samples incubated with or without added Zn. The percentage of added Zn which was extracted appears in parentheses. Zn + = Zn added (9.06 mg dnr 3 of soil), Zn- = native Zn. 1 Soil Zn„ Zn AAAc Zn Ac Zn DTPA HSD00, 18 Zn+ 1.42" 3.74' 9.40» 5.82b 0.47 Zn- 0.29' 0.68" 2.07» 0.91 b 0.35 Difference 1.13 (12%) 3.06 (34%) 7.33 (81%) 4.91 (54%) 34 Zn+ 7.26' 8.37" 10.65» 8.04"' 0.97 Zn- 1.90b 1.99" 2.95» 1.93" 0.29 Difference 5.36 (59%) 6.38 (70%) 7.70 (85%) 6.11 (67%) 78 Zn+ 4.04' 4.65' 11.75» 8.29b 1.06 Zn- 0.94' I.oB' 3.46» 1.79" 0.48 Difference 3.10 (34%) 3.57 (39%) 8.29 (92%) 6.50 (72%) 104 Zn+ 4.76" 4.18 b 10.66» 10.42» 0.83 Zn- 1.00" 0.95b 3.34» 3.70» 0.54 Difference 3.76 (42%) 3.24 (36%) 7.32 (81%) 6.72 (74%) 1 In each soil, the results of the samples incubated with and without added Zn were tested separately for each extraction. 226 Agric. Sei. Fint. 2(1993) Table 26. Soil Zn (mg dm 3) extracted by pyrophosphate (Znpy ) and oxalate (Znox ) from samples incubated with or without added Zn. The percentages of added Zn which was extracted appear in parentheses. Zn+ = Zn added (9.26 mg dnr 3 of soil), Zn- = native Zn. 1 Soil ZnTO Znox Sum H5D,,,,, 18 Zn+ 9.16" 4.34" 0.69 Zn- 1.39" 2.50* 0.23 Difference 7.77 (84%) 1.84 (20%) 9.61 (104%) 34 Zn+ 13.49' 3.34" 0.21 Zn- 4.71' 2.49" 0.21 Difference 8.78 (95%) 0.85 (9%) 9.63 (104%) 78 Zn+ 13.86" 1.03" 0.68 Zn- 5.01» 1.49b 0.27 Difference 8.85 (96%) 0.46 (5%) 9.31 (101%) 104 Zn+ 13.50» 0.98b 0.14 Zn- 4.14» 0.44" 0.24 Difference 9.36 (101%) 0.54 (6%) 9.91 (107%) 1 In each soil, the results of the samples incubated with and without added Zn were tested separately for each extraction. Adsorption of added Zn into the non-exchange- able form was observed especially in the clay soil (18) where as much as 88% of added Zn was not extracted with MgCb. This tendency was weaker in the loam (34) in which more than half of added Zn remained exchangeable. In mineral soils added Zn was more efficiently extracted by AAAc than by MgCb but in the organogenic soils these two solu- tions extracted added Zn equally effectively. De- spite the low pH of the organogenic soils, a consid- erable part of added Zn was adsorbed into forms not dissolved by MgCla or AAAc. This may be due to the formationof organic complexes, and the extrac- tion of this fraction seemed to require chelating agents (EDTA and DTPA). AAAc-EDTA dissolved 81 - 92% of added Zn, being thus the strongest extractant for added Zn in the two mineral soils and in the mull. In peat, AAAc-EDTA and DTPA were equal in efficiency. Despite its high pH, DTPA was a strong extractant for native and added Zn in organogenic soils, but in mineral soils DTPA was relatively less effective. As for added Zn, the results of AAAc-EDTA ex- traction were less affected by soil characteristics than those of the other extractions. Pyrophosphate extraction removed the bulk of added Zn from soil, the rest being dissolved by oxalate (Table 26). The residue of added Zn in the soil after pyrophosphate extraction seemed to be highest in the clay soil and lowest in the two or- ganogenic soils. The recovery of added Zn was not affected by soil pH. The apparent recovery ofadded Zn seemed even to exceed 100% in all soils. The recovery was calculated as the difference between the sums ofZnpy + ZnGx extracted from soils incub- ated with and without added Zn. The confidence limits at the 95% level were 0.2 - 0.3 mg dm' 3 for Znpy and 0.1 - 0.2 mg dm'3 for Zn ox* The present results were within these limits. 3.5 Discussion 3.5.1 Total Zn The Zntot in the surface soil material was higher than the results of spectrographic determination of Zntot published earlier in Finland (Vuorinen 1958, Erviö and Virri 1965, Sippola 1974). For ex- ample, in the study by Sippola (1974) Zntot ranged from 20 mg kg' 1 in sands to 78 mg kg' 1 in heavy clays. It is not likely that Zntot of the soils in Finland has doubled in a few decades but the difference may be attributed to the different methodologies 227 Agric. Sei. Fin!. 2 (1993) 1 employed. Later Zntot determinations carried out in Finland, based on digestion with HF-containing acid mixtures and measurement of Zn by AAS (Baghdady and Sippola 1983, Koljonen and MalisA 1991), have yielded results of the same magnitude as those of the present study. Because the methods of determining Zntot give different results, the following references include only studies in which unpolluted mineral soil samples have been completely decomposed with HF-containing acid mixtures and analyzed for Zn by AAS. The Zntot in soils of temperate climates, e.g. silt and clay loam soils of Denmark (Tjell and Hovmand 1978), clay, loam and sandy soils of Germany (Baghdady and Sippola 1983, Lichtfuss and Andresen 1983) and clay loam soils of various parts of Canada (Bishop and MacEachern 1973, Nielsen etal. 1986,Liang et al. 1990), are similar to or slightly smaller than those in the respective textural classes of the pre- sent material. Clay and clay loam soils of warmer regions, e.g. Virginia and Georgia, USA (IYENGAR et al. 1981, Shuman 1985) and the Nile delta, Egypt (Baghdady and Sippola 1983), have also had similar or slightly lower Zntot than occurs in texturally corresponding soils ofFinland. However, in unpolluted soils of other countries, Zntot seldom exceeds 150 mg kg’ 1 , a value commonly found in clay soils of Finland. In coarse sandy soils of warmer climates, i.e. Georgia, USA (Shuman 1985), and Australia (Brennan and Gartreli. 1990), Zntot is commonly below 10 mg kg’ 1 which is less than in any of the coarse mineral soils of the present study. A close correlation between clay content and Zntot is likely to be a consequence of the differences in soil mineralogy in the textural fractions (Sippola 1974). The analyses of clay and silt plus very fine sand of three soils directly showed that the coarser fraction was poorer in Zntot than was clay. How- ever, silt can occasionally be as rich in Zntot as is clay (Andersson 1979,Armour et al. 1990).This may be the explanation why the unpolluted soils of Kuhmoinen (soil 21) and Hollola (soil 38) had a higher Zntot than the other soils of similar clay contents. The negative correlation between Zntot and or- ganic C in organogenic soils reflects the origin of Zntot in mineral material. The studies on the vertical distribution of Zn emphasize that Zntot in organo- genic soils was dependent on Zntot of the mineral soil below the organogenic layers. Organogenic soils (profile P 6 from Jokioinenand the sample pair from Forssa) on a clayey subsoil were rich in Zntot- On the contrary, the Carex peat profile P 7 (Muhos), most probably also profile P 5 (Sotkamo), had de- veloped on coarse mineral soils poor in Zntot with the consequence that also the organogenic layers were poor in Zntot- In mull and peat soils, the mean Zntot was 48.7 and 35.1 mg kg' 1 , respectively, whilea higher mean of 65.5 mg kg' 1 was measured in 55 cultivated Histosols of Canada (Levesque and Mathur 1986). Nine out of the 20 peat soils of the present study contained less Zn than was the minimum (28.5 mg kg' 1 ) in the peat soils of Canada. This comparison confirms that soils extremely poor in Zntot prevail among cultivated peat soils of Finland. Moreover, the results of URVAS et al. (1992) sug- gest that the peat soils of this study did not even contain the poorest ones occurring in Finland. However, Zntot in cultivated peat soils ofFinland commonly exceeds that in virgin peatlands of Ger- many where a Zntot of5 -50 mg kg' 1 (mean 20 mg kg' 1 ) has been measured (Teicher et al. 1987). 3.5.2 Fractions ofsoil Zn The decreasing trend of Zn e x with increasing soil pH agrees with the results of several studies (Sims andPATRiCK 1978, Nielsen etal. 1986,Sims 1986, Palko and Yli-Halla 1990),reflecting the corre- sponding increase of specific adsorption of Zn. In mineral soils, Zn ex was of the same level as in other studies on acid mineral soils (IYENGAR et al. 1981, Shuman 1985, Nielsen et al. 1986). Even in very acid clay soils Zn tended to be bound by covalent forces to a larger extent than in the coarsest mineral soils of similar pH. This may reflect the abundance of sites capable of specific adsorption ofZn in clay soils, which were richer in organic matter and Fe oxide, important components adsorbing Zn in acid soil (Mcßride and Blasiak 1979,Brummer et al. 228 Agric. Sd. Finl. 2 (1993) 1983, Tiller et al. 1984, Pulford 1986). In or- ganogenic soils, the high percentage of Zntot in exchangeable form was probably attributable to the strong acidity in these soils. In a few peat soils, more than 30% of Zntot was exchangeable, which suggests that the small native reserves of Zn in these soils may even be susceptible to leaching. A few observations corroborate that sequential pyrophosphate and oxalate extractions dissolved Zn by and large from different soil components. First, Znpy (mg dm ) was approximately equal in all soil classes while Zn ox decreased in the mineral soils with decreasing clay content. Second, unlike Znpy , Zn 0x correlated significantly with Zntot. The fraction of ZnPy has been assumed to consist of Zn bound by organic matter. In the present study Znpy or complexed Zn (Znpy - Zn ex) did not correlate with organic C, but the dark color of the pyrophos- phate extracts and the appearance of the soil after the extraction suggest effective removal of organic matter, with the consequence that also most Zn bound by organic matter was probably extracted. Pyrophosphate may also dissolve Zn from other sources. Oxides ofFe, Al and Mn are major adsorb- ents for Zn added to soil (e.g. Mullins et al. 1982, Mcßride 1989). In an incubation experiment of the present study the bulk of Zn added to soil was extracted with pyrophosphate and only a minorpart was recovered as Znox which was supposed to rep- resent sesquioxide-bound Zn. This observation in- directly suggests that at least some Zn from sesqui- oxides is extracted with pyrophosphate. The hy- pothesis is supported by an observation that pyro- phosphate dissolves Fe from sesquioxides (BaS- COMB 1968). There was some evidence that in mineral soils the occurrence ofZnD x may indeed be connected to Fe oxides. There was a correlation between Zn 0 x and Fe 0x, and the lowest Zno x exclusively occurred in the mineral soils poorest in Feo x. Several organo- genic soils were also rich in Fe0x, but contrary to the mineral soils this was not connected to the abund- ance of Znox- Moreover, in organogenic soils Zn o x did not correlate with Znres or organic C which reflect the quantity of mineral material in the soil. Therefore, the source of Zn0x in organogenic soils requires further research. The mean percentage ofZnox was low compared to the results of comparable sequential extraction studies from Georgia and Virginia, USA (Shuman 1979, Iyengar et al. 1981), and from the Nile delta, Egypt (Elsokkary 1979). In those soils, scarce in organic matterand rich in crystalline Fe oxide, Zn ox was the major fraction of secondary Zn, amounting to 25% ofZntot. Inversely, in the temperate soils of Canada (Nielsen et al. 1986, Liang et al. 1990) the Zn0x fraction was of the same magnitude (below 5% of Zntot) as in the present material. Oxalate is not selective for poorly crystalline ox- ides but over time also crystalline oxides are dis- solved (Borggaard 1979, 1992). In the present sequential extraction, poorly crystalline oxides and Zn bound by them may have been removed already in the pyrophosphate treatment and only the Zn bound to more crystalline oxides may have re- mained in the successive oxalate extraction. The scarcity of Znox in temperate soils may thus be attributed to the small quantity of crystalline ox- ides, owing to the young age and high content of organic matter which retards crystallization. The hypothesis presented above may be valid especially in organogenic soils most of which were poor in Zn Qx. Pyrophosphate and oxalate extractions com- pletely removed Zn which had recently been added to the soil. The strong extraction power of these solutions was also shown by Payne et al. (1988) who observed that Zn added to a Rhodic Paleustult (560 kg Zn ha" 1 during 17 years) was recovered as Zn Py and Zn 0x, but there was no accumulation in the residual fraction. It seems therefore justified to regard the sum Znpy + Zn ox as the quantity of secondary Zn. In most studies from other countries, the percent- age of Znres in mineral soils has been lower than that in the present mineral soils where approx- imately 90% of soil Zn occurred as Znre s. For ex- ample, in soils of the British Columbia and Sas- katchewan, Canada (Nielsen et al. 1986, Liang et al. 1990), Znres amounted to 71% and 83% (ranges 46 - 93% and 69 - 91%, respectively). Results of that level have also been obtained in soils of Dela- ware and Georgia, USA (Iyengar et al. 1981, SHU- MAN 1985), while in alluvial soils of Egypt, Znres 229 Agric. Sei. Fint. 2 (1993) was only 45% of Zntot (range 39 - 61%) (Elsok- kary 1979). The higher percentage of Znres in the present study reflects the young age of soils of Finland. The result also shows that the cultivated soils ofFinland are not polluted with Zn because in polluted soils Znres represents a smaller fraction of Zntot (LÅG and Elsokkary 1978, Räsänen and Hämäläinen 1991). The high percentage of secondary Zn in the organogenic soils reflects the scarcity of primary minerals in these soils. Application ofmanures, sludges and Zn-contain- ing mineral fertilizers as well as atmospheric depo- sition of Zn can result in excessive accumulation of secondary Zn in surface soil (Berndt and Ker- shaw 1989, Driel and Smilde 1990). Owing to mineral additives of fodder, manures in Finland commonly contain more than 200 mg Zn kg" 1 in the dry matter (Kemppainen 1989).The present results showed that also in Finland there are soils where abundant use of manure has resulted in elevated reserves of secondary Zn. The high concentration of Zn in soil 71 of Harjavalta was probably due to atmospheric deposition of Zn from the local metal industry which for example in 1988 emitted 100 000 kg of Zn, approximately 17% of all indus- trial Zn emissions of the country (Aunela and Larjava 1990). Even though this single soil sample is not necessarily representative, this obser- vation warrants concern for excessive Zn content of soil in the vicinity of metal industry. However, the Zn concentration of this sample was much lower than the extreme values exceeding 1000 mg kg’ 1 in the secondary fractions in soils heavily polluted by Zn (Elsokkary and Låg 1978, Folkeson and Andersson-Bringmark 1988, DeLaune et al. 1989, Jordao and Nickless 1989). Also in Fin- land, highly elevated concentrations of Zn have earlier been reported in lake shore sediments and surface soils of industrial areas (Räsänen and Hämäläinen 1991). 3.5.3 AAAc-EDTA extractions In unpublished material of Soil Analysis Service Ltd., the means of ZnAc were 5.0, 6.1 and 4.9 mg dm"'1 in the 1262,10240and 11701 analyses carried out in 1986, 1987 and 1988, respectively (results available at Soil Analysis Service Ltd., P.O. Box 500, FIN-50101 MIKKELI). Also the means and distributions of ZnAc in 2015 cultivated grassland soils ofFinland (Sippola and Tares 1978) were of the same magnitude as those of the present mater- ial. On the contrary. Sillanpää (1982) and Urvas et al. (1992) presented results on 90 mineral soils and 112 organogenic soils in which ZnAc was con- • 2siderably smaller (mean 2.7 and 2.1 mg dm , re- spectively). Because the present results correspond to those of the large materials of Soil Analysis Service Ltd. and Sippola and Tares (1978), it is justified to conclude that the observations made on the material can be extended to the cultivated soils ofFinland in general. The extractant AAAc-EDTA consists of three components: (1) acetic acid, (2) ammonium acetate and (3) Na2-EDTA. The chemical nature of ZnAc can be assessed by studying the fractions which might be extracted by each component alone. It is likely that the aqueous solution extracts water-sol- uble Zn, and Zni+ bound by electrostatic forces is exchanged by NH4 + cations of the solution.AAAc- EDTA extracted more Zn than did MgCh, the dif- ference being especially pronounced at the high pH range of the experimental soils. In several studies, 2.5% CH3COOH has been used in the extraction of Zn specifically adsorbed on the surfaces of sesqui- oxides (Elsokkary and Låg 1978, Iyengar et al. 1981, Payne et al. 1988). In AAAc-EDTA, the concentration ofacetic acid is 3% and therefore it is likely that specifically adsorbed Zn is extracted also by AAAc-EDTA. This assumption is supported by the observation that increasing clay content en- hanced the extraction power of AAAc-EDTA in relation to MgCb in mineral soils. In clay soils the number of sites available for specific adsorption of Zn is probably higher than in coarse mineral soils, owing to the higher contents ofFe ox and Alox- EDTA has been added to the AAAc solution in order to enhance the extraction of metallic trace elements (Lakanen and Erviö 1971). However, the Zn-EDTA complex is most stable at pH 6.5 (Lindsay 1972), and pH 4.65 should theoretically be far from ideal in order to facilitate effective extraction of Zn by EDTA. Yet, the extraction ex- 230 Agric. Sei. Fint. 2 (1993) periment (Section 3.4) showed that EDTA in- creased the extractability of both native and added Zn especially from organogenic soils as compared to the extraction by AAAc alone. Moreover, the extraction power of AAAc-EDTA was at least equal to that of DTPA where the pH 7.3 corre- sponds to the pH of maximum stability of the Zn- DTPA complex (Lindsay 1972). EDTA is an ef- fective extractant for organically bound Cu (Rashid 1974,Stevenson 1982,p. 40). It has also been observed that the addition of EDTA in the Mehlich 2 extractant (CH3COOH - NH4CI - NH 4F - HCI) enhanced the extractability of soil Zn espe- cially when the content of organic matter increased (Mehlich 1984). It may thus be assumed that also AAAc-EDTA extracts Zn bound by organic matter even at pH 4.65. However, organic matter is more effectively extracted by pyrophosphate than by EDTA (McLaren and Crawford 1973). This ob- servation seems to apply also to organically bound Zn because in mineral soils the extraction power of AAAc-EDTA decreased in relation to pyrophos- phate with increasing content of organic C. The close correlation between ZnAc and Znpy suggested that AAAc-EDTA extracted Zn mainly from the same sources as did pyrophosphate. It may thus be concluded that, in addition to water-soluble and exchangeable Zn, the AAAc-EDTA extracts Zn specifically adsorbed by sesquioxides and organic matter. Goldschmidt (1937) observed in Germany and Hibbard(1940) in California, USA higherconcen- trations of Zn extracted from surface soils as com- pared to the subsoil. They both suggested inde- pendently that this may be due to bioaccumulation as a result of uplift of Zn from deeper layers by plant roots. When plant residues are decayed, Zn from plant tissue is mineralized and retained in the surface soil. The hypothesis of bioaccumulation is also corroborated by the observations on the pre- sent mineral soil profiles and earlier in a more extensive material ofpeat soils of Finland (Urvas 1986). In the present fine-textured mineral soil pro- files, the minimum ZnAc occurred in the upper part of subsoil, and a higher concentration of ZnAc was measured deeper in the profile. Zinc uptake by plant roots may have depleted the reserves of ZnAc in the upper part of subsoil but not in the deeper layers because roots of herbaceous plants do not penetrate to a considerable extent deeper than 1 m (Dwyer et al. 1988). This observation also sug- gests that bioaccumulation of Zn is an important factor contributing to ZnAc in the plough layer. Absence ofcorrelationbetween Znre s and ZnAc also suggests that a considerable part ofsecondary Zn in the surface soil may not have been released from the primary minerals residing in the plough layer but may have been brought there from external sources, e.g. by bioaccumulation and atmospheric deposition. 4 AVAILABILITY OF SOIL AND FERTILIZER ZINC TO RYEGRASS IN POT EXPERIMENTS 4.1 Availability of soil Zn 4.1.1 Experimental In order to examine the potential of soil to supply plants with Zn, a pot experiment was arranged with 107 plough layer samples (Appendix 2). Four crops of Italianryegrass (Lolium multiflorum , Lam.) were grown in plastic boxes containing 0.2 dm3 of ground (< 2 mm) soil (two replicates). Nutrients, except Zn, were applied to each crop at the follow- ing rates (mg dm of soil) as analytical grade chemicals: "3 Element Rate, mg dm ~ Compound N 300 NH4NO3 P 80 KH2PO4 K 200 KCI, KH2PO4 Mg 50 MgSO4 • 7H20 S 67 MgSO4 • 7H20 231 Agric. Sei. Fin!. 2 (1993) Agric. Sd. Fint. 2 (1993) Micronutrient fertilization, including 5 mg S dm , was applied at the beginning of the experi- ment and after the second harvest at the following rates: Element Rate, mg dm'3 Compound Cu 3 CuSOa • 5f3 CuSOa • 5H2 0 Mn 4 MnS04 • 4H 20 Fe 2 FeS04 • 7H 20 B 0.5 H3803 Mo 1 Na2M004 • 2H2 C) At the beginning of the experiment, the fertilizer solutions were mixed in the soil.For the subsequent crops they were pipetted onto the surface of the soil. To prevent a decrease of pH in the course of the trial due to N fertilization and root exudates, 250 mg of Ca(OH)2 (6.8 meq dm'3 ) was mixed into each pot. The seeds (250 mg per pot) were covered with 150 ml of quartz sand washed with 3 M HCI. The pots were watered with deionized water once or twice a Table 27. Change in pH during the pot experiment in the five soil classes. Soil class Change in pH Mean s Range Clay -0.24b 0.21 -0.57-0.06 Silt, loam, -0.31b 0.22 -0.61-0.10 very fine sand Fine sand, moraine -0.35 b 0.15--0.6 0.05 Mull -0.19ab 0.19 -0.40-0. n Peat -0.10" 0.15 -0.36-0.18 day. The first crop was cut 29 days after sowing, and the average growing period of the successive crops was 24 days. The yields were dried at 60°C, weighed and analyzed for Zn. At the end of the experiment, the pH of the soil in the pot was deter- mined. In spite of the lime application, soil pH decreased during the experiment (Table 27). 4.1.2 Dry matter yields The mean deviation of the total dry matter yield between the two replicates was 0.30 g per pot, or 3.1% of the average yield. The average total dry matter production (sum of four crops) in clay, silt loam and very fine sand soils was slightly higher than that of the organogenic soils (Table 28). Dry matter yields did not correlate with any of the indi- ces of secondary Zn of soil. Dry matter production in mineral soils was positively correlated with Zntot (r = 0.48** ) and soil pH (r = o.34* **). The correla- tion between Zntot and the yield reflects the trend that fine sand and moraine soils, poorer in Zntot than the clay soils, tended to produce smaller yields than did the more fine-textured soils. In organo- genic soils, dry matter yield did not correlate sig- nificantly with the soil properties measured. 4.1.3 Zinc concentration and uptake The mean Zn concentrationof the grass within each yield (Table 29) did not differ markedly from one soil class to another (HSD values not presented). Table 28. Dry matter yields of ryegrass. l Successive crop, g per pot Sum of yields, g per pot Soil class n I II 111 IV Mean Range Clay 25 2.273.36 2.52 2.13 10.28ab 9.13-11.52 Silt, loam, very fine sand 20 2.413.39 2.482.15 10.43» 9.45-11.48 Fine sand, moraine 28 2.262.97 2.382.10 9.71>* 7.96-11.43 Mull 14 2.152.90 2.34 2.00 9.39< 7.69-10.39 Peat 20 2.11 2.78 2.34 1.97 9.20- 7.78-11.31 1 Means in each column were tested separately. 232 Table 29. Zinc concentration (mg kg ') of ryegrass in the pot experiment. The results of the fine sand and moraine soils excluding those of soil 71 are presented in parentheses. l Soil class Crop Mean s Range Clay I 32.4» 10.6 13.5-49.5 n 25 II 23.4" 6.9 12.0-34.5 111 36.2» 11.2 19.0-64.5 IV 36.8" 11.5 16.5-61.0 HSD005 4.0 Fine silt, loam, very fine sand 1 27.5 b 10.4 11.5-50.5 n = 20 II 20.6C 6.8 11.0-38.0 111 31.8» 7.6 18.5-42.0 IV 29.4» b 7.8 16.0-44.0 HSD„ OS 3.9 Fine sand, moraine I 30.1"((28 .b)5 b ) 13.7(10.7) 14.0-75.5(54.5) n= 28 11 27. 0 b (24.9 b ) 18.7 (10.2) 11.0-109 (52.0) 111 38.6» (34.1") 26.1 (13.3) 17.5-154 (67.0) IV 42.0» (36.3») 34.2 (15.7) 16.0-198 (76.0) HSD005 7.8 (5.3) Mull I 35.0» 5.9 21.5-42.0 n = 14 11 25.1" 6.0 13.0-35.5 111 31.4» 8.7 15.5-47.0 IV 30.6» 9.1 15.5-46.0 HSD00! 4.8 Peat 1 34.3» 10.2 17.0-56.5 n = 20 II 28.2b 8.7 13.0-49.0 111 30.8» b 10.8 11.5-57.5 IV 30.0b 10.0 12.0-53.3 HSD005 3.6 1 Results of each soil class have been tested separately. Table 30. Mean Zn uptake of grass by the four yields. l Soil class Zn uptake (ug dm 3) by successive crops HSD,)OS ue dnv 1 1 II 111 IV Clay 400» 380» 400» 410» 74 Silt, loam very fine sand 330 b 350ab 400» 320 b 51 Fine sand, moraine 330" 400ab 440a 450» 81 -soil 71 excluded 310 b 370ab 400» 380» 61 Mull 380» 370» 370» 310" 50 Peat 360» 390» 360» 290" 49 1 Results of each soil class have been tested separately, Each soil class, particularly fine sand and moraine, contained a few soils (especially soil 71) which produced grass very rich in Zn as compared to the bulk of the material. There was a tendency of Zn concentration to be the lowest in the second crop in which the largest quantity of dry matter was pro- duced. In peat soils, the mean Zn content in the fourth crop was lower than that in the first one, while in the mineral soils Zn concentration in the last two crops was at least as high as in the first one. Uptake of Zn (Table 30) was calculated by mul- tiplying the dry matter yield with Zn concentration 233 Agric. Sei. Fin!. 2 (1993) of the respective grass sample. Because the roots were not weighed and analyzed, Zn uptake repre- sents the quantity of Zn transported to the above- ground parts of ryegrass. In clay soils, Zn uptake remained constant from crop to crop, whereas in silt, loam and very fine sand soils, the maximum Zn uptake occurred in the third crop. Instead, in the fine sand and moraine soils, Zn uptake increased towards the end of the experiment, despite decreas- ing dry matter production. Because both Zn con- centration and uptake increased, the Zn supply to plants can be assumed to increase over time in these soils. In organogenic soils, Zn uptake by the fourth crop was smaller than that by the three earlier ones. In peat soils, both concentration and uptake were smaller in the fourth crop, which may reflect a decreased Zn supply to the plants. Within a crop, the only statistically significant difference in Zn uptake between the five soil classes occurred in the fourth crop in which Zn uptake from clay soils was greater than that from the peat soils (HSD values not presented). The cumulative Zn uptake in the four yields ranged from 620 to 6190 pig dm of soil, mean 1470 pig dm' . The mean deviation in Zn uptake between thereplicates was 52 pig dm' , correspond- ing to 3.7% of the mean. The differences in Zn uptake were much greater within each soil class than between the classes which did not differ sig- nificantly from one another. Correlation between plant Zn concentration and Zn uptake was very close in each of the four crops (r = 0.87 -0.96 ) but negligible between the cumulative dry matter yield and Zn uptake (r = 0.08ns ' and r = 0.26ns' in mineral and organogenic soils, respectively). Thus, the quantity of Zn taken up was by and large deter- mined by the Zn concentrationof the plant material. 4.1.4 Dependence ofZn uptake on soil properties The correlation coefficients between a few soil characteristics and the cumulative Zn uptake in the four crops are presented in Table 31. In the calcula- tions, natural logarithms (log e) of soil Zn concen- trations (mg dm’3 ) were used. The results ofsoil 71 were not included in the calculations. In organo- Table 31. Linear correlation coefficients between soil characteristics and Zn uptake by the four ryegrass crops. Natural logarithms of soil Zn concentrations (mg dm 5) were used in the calculations. Mineral soils Organogenic soils n = 72 n = 34 0.80*" 0.83*" 0.60*" o.6B*** 0.80*" 0.37 ns- -0.1sns5ns _o.i ins. 0.89*" 0.82"* 0.51*" 0.77'" 0.64"* 0.18" s- -0.27* -0.03 ns- ZnAc Znpy Znox Zn„ Znpy -Znex Zn,ot pH Organic C genie soils, Zn uptake correlated most closely with Zripy, ZriAc, Zriex and Znpy - Zn e x. In mineral soils, Zn uptake correlated more closely with ZnAc than with Zn ex and Znpy - Zn ex , and more closely with Znpy than with Znpy-Znex . The partial correlation coefficients between Zn uptake and Znpy - Znex, when eliminating the effect of Zn ex, were highly significant (r = 0.56 and 0.65 in mineral and organogenic soils, respectively), suggesting that also complexed Zn contributed to plant-available Zn. The correlation coefficient with Zn o x was also significant, but the partial correlation coefficient between Znox and Zn uptake, when the effect of Znpy was eliminated, was not statistically signific- ant. The relationship between ZnAc and Zn uptake in mineral and organogenic soils is presented in Figures 3 and 4, respectively. In the multiple regression analysis, ZnAc (mg dm’ ), soil pH and organic C (%) explained 82% of athe variation of the cumulative Zn uptake (pg dm' ofsoil) in mineral soils. In an equation consisting of Znpy (mg dm’3), Znox (mg dm'3) and pH, the coef- ficient of multiple determination was slightly lower. At a given level of Znpy , Zn ox and ZnAc, Zn uptake decreased with increasing soil pH. Accord- ing to the beta coefficients (Table 32), ZnAc and Znpy were by far the most important soil charac- teristics determining the magnitude ofZn uptake by the grass. The two equations for mineral soils (n = 72) were as follows: 234 Agric. Sei. Finl. 2 (1993) Zn uptake = 593 loge Zn Ac - 188pH - 40.8 C + 2150 R 2 = 0.82 Zn uptake = 439 loge Znpy + 222 loge Zn ox - 202 pH + 1940 R 2 = 0.73 The dependence ofZn uptake of each crop on the characteristics of mineral soils was also studied. Within each crop, ZnAc and Znpy (loge of theresults expressed as mg dm' ) were the most important soil characteristics explaining the variation of plant Zn uptake (|4g dm 3 of soil) (Table 33). Soil pH was significant in the first two crops but lost signific- ance towards the end of the experiment. Also the pH measured at the end of the experiment was used Table 32. t-Values of the regression coefficients and beta coef- ficients (P) of the independentvariables of the regression equa- tions explaining Zn uptake by ryegrass in mineral soils. Independent variable t P logc ZnAc 16.270'" 0.85 pH I -4.041"* -0.24 Organic C -2.344* -0.14 logc Zn,„ 6.837*" 0.61 logc Zn„N 3.203" 0.30 pH 2 -3.200" -0.26 lin the equation with log, Zn Ac and organic C 2in the equation with log, Znpy and Zn ox as an independent variable, but it did not prove statistically significant even in the last two crops. On the contrary, Zn Gx was significant in the last crop. Increasing clay content (%) promoted Zn up- take, but increasing organic C (%) had a negative impact. When Znpy was divided into two compo- nents (Znex and Znpy - Ztiex) they were both signi- ficant (beta coefficients not shown), and the equa- tions had nearly the same coefficients of multiple determination as those containing Znpy . In multiple regression analyses of the results of organogenic soils, the cumulative Zn uptake (ug 3 3dm "of soil) was explained only by ZnAc (mg dm ‘) or Znpy (mg dm'3 ), without a statistically signific- ant contribution of soil pH or ZnG x- The two altern- ative regression equations were as follows (n = 34): Zn uptake = 404 loge Zuac + 894 O *** R 2 = 0.64 Zn uptake = 389 loge Znpy + 863 9 **sjt R“ = 0.69 4.1.5 Utilization of soil Zn reserves The relative utilization of Zntot, expressed as the percentage of Zntot taken up by the four crops of ryegrass, averaged 5.1% of Zn tot (median 2.2%, Fig. 3. Dependence ofZn uptake of four ryegrass crops on the concentration of soil Zn extracted by AAAc-EDTA (ZnAc) in mineral soils. Fig. 4. Dependence ofZn uptakeof four ryegrass crops on the concentration of soil Zn extracted by AAAc-EDTA (ZnAc) in mineral soil. 235 Agric. Sei. Finl. 2 (1993) Table 33. Beta coefficients of independentvariables explaining Zn uptake of the four ryegrass crops (I-1V) in mineral soils (n = 72), as well as the coefficients of multiple determination (R 2 ) of the respective regression equations. Natural loga- rithms of soil Zn concentrations (mg dm 3) were used in the calculations. Crop Zn At Znpy Zn0I pH Org. C, % Clay, % R; I 0.68 - - -0.46 n.s. n.s. 0.75"* I - 0.64 n.s. -0.42 n.s. n.s. o.7l*** II 0.76 - - -0.37 -0.16 n.s. 0.76*" II - 0.68 n.s. -0.36 -0.240.17 0.65*" II - 0.660.24 -0.36 0.62"* 111 0.82 - - n.s. -0.220.14 0.77'" 111 - 0.79 n.s. n.s. -0.290.26 0.71*" 111 - 0.660.21 n.s. 0.64"' IV 0.77 - - n.s. -0.24 n.s. 0.65"* IV - 0.610.24 n.s. -0.21 n.s. 0.64*" = Not included in the calculations. Table 34. Relative utilization of Zn,ot and secondary Zn (Znpy + Zn ox) by ryegrass in the pot experiment.l Soil class n Utilization of Zn, M , % Utilization of Znpy + Zn,„, % Mean Range Mean Range Clay 25 1.3» 0.6-2.5 23.1 6.6-36.2 Silt, loam, very fine sand 20 1.6b 0.7-3.7 25.5 14.6-39.4 Fine sand, moraine 27 3.3 f 0.8-8.6 24.5 6.4-48.6 Mull 14 5.V 2.3-10.0 28.4 12.1-49.6 Peat 20 15. l> 3.7-40.3 33.1 6.8-68.8 1 Means in each column were tested separately. range 0.6 - 40.3%). It was greater in the peat soils as compared to the other soils (Table 34). In or- ganogenic soils there was a correlation(r = 0.80 ) between organic C and utilizationofZntot, which is explained by the inverse relationship between or- ganic C and Zntot- In five out of 20 peat soils Zn uptake exceeded 20% of Zntot- In mineral soils, decreasing pH promoted the utilization ofZntot (r = 0.42 ), and clay content correlated negatively with the relative utilization of Zntot (r = -0.51 ). This is because clay content correlated with Zntot, but Zn in the fine-textured mineral soils was to a higher extent in the residual fraction unavailable to plants. In the short term, secondary Zn fractions serve as the reserve of plant-available Zn in soil. Therefore, rather than utilization of Zntot, it is more appropri- ate to investigate the use of secondary Zn reserves. Relative utilization of secondary Zn in soil is af- fected by the size of the reserves as well as by their availability. For example, a given Zn uptake by the crop corresponds to a stronger relative utilizationof Zn in a soil which has small reserves as compared to another soil which contains more Zn in a plant- available form. Strong relative utilization ofsoil Zn may reflect the tendency of those reserves to be exhausted by plant uptake. Zinc uptake by ryegrass corresponded on average to 109% of Zriex and ranged 15 - 535%. This result suggests that in addi- tion to the water-solubleand exchangeable fraction, also less soluble Zn must have been taken up in several soils. Therefore the emphasis of studies on the relative utilization of soil Zn was in the Znpy and Znox fractions. 236 Agric. Sd. Finl. 2 (1993) The relative utilization of secondary Zn was calculated as the ratio of Zn uptake (me: dm'3 ) to the sum Znpy + Znox (mg dm"3 ), i.e. 100 •Zn uptake/(Znpy + Zn ox ). Because the up- take of Zn in a pot experiment was used in the calculation of this index, the validity of the nu- merical values obtained is limited to this particular experiment. Zinc uptake amounted to 27.3% of Znpy + Zn0x, the range from 1.8% in soil 71 to 68.8% in peat soil 97 (Table 34). The secondary Zn fractions were utilized on average slightly more effectively in peat soils than in mineral soils, but the differences were not statistically significant. In 11 soils (two coarse mineral soils, two mull soils, seven peat soils) poor in Zn the relative utilization of secondary Zn reserves exceeded 40%. Because correlation and regression analyses did not describe accurately the relationships between different soil characteristics and therelative utiliza- tion of secondary Zn, the quartiles of this index were investigated. The quartiles were designated I - IV according to increasing relative utilization of secondary Zn (Table 35). Coarse mineral soils were evenly distributed but in several clay soils Zn re- serves tended to be poorly utilized, while in several organogenic soils strong relative utilization was observed. The quartiles of relative utilization of secondary Zn were compared to those of Zn uptake. There were soils of all possible combinations of these two dimensions (Table 36). Large reserves of soil Zn were in most soils connected to a weak relative utilization, but small reserves were not necessarily effectively utilized by the grass. The four extreme groups of soils, shaded in the comers of Table 36, were studied in more detail. These soils were sup- posed to possess outstanding characteristics con- nected to given patterns of utilization of soil Zn. The rest of the soils were supposed to have the same characteristics less illustratively. The four extreme groups of soils were as follows: Group 1: combination of high Zn uptake (1720 - 3 ...6190 |ig dm ) (quartile I) and weakrelative utihza- tion of secondary Zn (quartile I). The group con- sisted of 12 soils of large Zn reserves. All the seven soils containing more than 10 mg ZnAc dm oc- curred in this group. Soil pH (5.3 - 7.2) was of Table 35. Distribution of soils of different classes into quar- tiles (F251f0 ) of relative utilization of secondary Zn reserves (Znpy + Zn ox). The quartiles are designated I-1V according to increasing relative utilization of secondary Zn of soil. Quartile Relative Soil class utilization ~~ „r -7 >7 Clay Coarse Organo-of Zn +Znm , ' e . ~ soils mineral genie soils soils I 1.8-19.5 6 13 8 II 19.6-25.5 11 9 7 111 25.7-30.9 5 16 6 IV 31.2-68.8 3 10 13 Table 36. Distribution of soils into quartiles (F25%) of Zn up- take by ryegrass and into quartiles of relative utilization of secondary Zn (Znpy + Zn ox ) of soil. Quartile of relative Quartile of Zn uptake2 utilization of - - secondary Zn' I 12 7 3 5 II 7 7 9 3 111 6 7 4 11 IV 2 6 10 8 ' The quartiles are designated I-IV according to increasing relative utilization of secondary Zn of soil. ; The quartiles are designated I-IV according to the decreasing Zn uptake minor importance in these soils with excessive re- serves of plant-available Zn. Group 2: high Zn uptake (quartile I) and strong relative utilization(39%) of secondary Zn (quartile IV). The group contained only one very fine sand (40) and one peat soil (99). These soils were acid (pH 4.2 and 5.5) and the ZnAc (2.9 and 3.5 mg dm 3 ) was around the median of the material. These soils are examples of rapid reduction of Zn reserves which were at least average in size. Owing to a small number of soils, this group was improperly portrayed. Group 3\ strong relative utilization of soil Zn (quartile IV) and low Zn uptake by plants (quartile IV). This group consisted of one gyttja clay (soil 12), three fine sands (50, 51 and 66) and four or- 237 Agric. Sei. Finl. 2 (1993) 238 Agric. Sei. FM. 2 (1993) Table 37. Soils showing a small Zn supply to ryegrass anc strong relative utilization of secondary Zn reserves (group 3). Soil Org. C pH ZnAc Znpy+ Zn ox Zn uptake Utilization % mg dnr 5 mg dnr 3 Hg dnr3 of Znpy + ZnOX! % 12 9.55.4 1.52.9 950 33 50 1.36.3 2.13.8 1170 31 51 2.46.4 1.73.4 1060 31 66 6.15.4 1.32.2 1070 49 83 21.55.6 0.81.6 790 50 97 38.85.5 1.80.9 620 69 98 39.84.9 1.52.1 940 45 103 47.34.8 0.61.0 660 65 Table 38. Soils showing a small Zn supply to ryegrass and low relative utilization of secondary Zn reserves in soil (group 4). Soil Org. C pH ZnAc Znpy+ Zn011 Zn uptake Utilization °7o mg dm- 3 mg dnr 3 Hg dnr 3 of Znpy + Zn ox , °7o 21 3.26.4 2.37.6 1020 13 28 0.86.6 0.84.5 760 17 38 4.86.4 1.46.6 1070 16 69 1.57.4 2.77.2 690 10 ganogenic soils (83, 97, 98, 103) (Table 37). These soils, except soil 50, belonged to the smallest quar- tile of ZnAc- The four organogenic soils were even within the Fio% of strongest relative utilization of secondary Zn as well as in the smallest Fio% of Zn uptake. Zinc uptake in these soils was thus limited by the small reserves. Group 4: low Zn uptake (quartile IV) con- nected with weak relative utilization of soil Zn (quartile I). In the four mineral soils of this group (Table 38) soil pH was distinctly higher, and Zntot, ZnP y + Zn 0x, and ZnAc were higher than in group 3, but ZnAc was below the median of the material (2.9 mg dm "). Zinc uptake by the grass was thus limited by relatively small reserves of Zn which, owing to a rather high pH, were poorly available. In groups 3 (low uptake, strong relative utiliza- tion of secondary Zn ) and 1 (high uptake, weak relative utilization) the soils had the most distinct- ive characteristics. Also some characteristics of the combination ofweak relative utilization and low Zn uptake (group 4) could be defined. Groups 3 and 4 exhibited two different combinations of charac- teristics resulting in a limited Zn supply to plants, Group 3 contained soils with small Zn reserves which, owing to the strong acidity, had a high avail- ability to plants, resulting in a strong relative utilization. In turn, the soils of group 4 had larger Zn reserves which, owing to a higher pH, showed a poorer availability resulting in a weak relative util- ization of these reserves. These conclusions are supported by the differentpatterns of Zn concentra- tions of grass grown in the organogenic soils of group 3 and in the mineral soils of group 4 (Figure 5). In the organogenic soils of group 3, the Zn concentration of grass decreased from crop to crop, suggesting declining reserves ofplant-available Zn in soil. In group 4, the Zn concentration of plants increased during the experiment, suggesting in- creased availability, probably owing to acidifica- tion of the soil in the course of the experiment. 4.2 Effect of Zn application on plant Zn concentration 4.2.1 Experimental A pot experiment was carried out in order to study the relationships between soil characteristics and the effect of Zn application on Zn concentration of ryegrass. The experiment was carried out in the same way as the one presented earlier (Section 4.1) with the exception that the pots were not limed. Zinc (10 mg dm"3 ofsoil) was applied as a solution of ZnSOa. One crop of Italian ryegrass was grown for 30 days in polythene boxes containing 0.2 dm of soil. There were two pots of each soil to which Zn was applied; two pots were grown without added Zn. Of the 107 surface soils (Appendix 2), 101 soils were available for this trial. Those not available (15, 27, 29, 51, 88, 107) were of average characteristics. 4.2.2 Dry matter yields and plant Zn concentrations The average dry matter production was 3.23 g per pot; the highest yields were nearly double the low- est ones (Table 39). The mean deviation of dry matter yield between the two replicates was 0.10 g per pot, or 3.1% of the average yield. The yields grown without added Zn correlated closely (r = * + + 0.88 ) with the yields fertilized with Zn. Accord- ing to the paired t-test, Zn application did not affect the size of the yield in any of the soil classes. The yields were not increased by Zn application even in soils producing grass with the lowest Zn concentra- tion. The mean deviationofZn concentrationbetween the two replicates was 1.6 mg kg' 1 and 1.0 mg kg' 1 in pots grown with and without applied Zn, corre- sponding to 4.5% of the mean in both treatments. The average Zn concentration of grass grown in mineral soils without applied Zn (19.5 mg kg' 1 ) was Fig. 5. Zinc concentration of four ryegrass crops grown (a) in very acid peat soils (group 3) where a strong relative utilization of secondary soil Zn was measured and (b) in slightly acid and neutral mineral soils (group 4) where a weaker relative utilization of secondary soil Zn occurred. 239 Agric. Sei. Finl. 2 (1993) Table 39. Dry matter yields, Zn concentration and Zn uptake of ryegrass in a pot experiment. Zn- = no Zn applied, Zn+ = Zn applied. Soil class Dry matter g per pot Zn concentration mg kg-' Zn uptake pg dm 5 Mean 1 Range Mean2 Range Mean2 Clay Zn- 3.32® 2.79-3.86 21.8* 11.5-35.0 Zn + 3.34® 2,12-3.77 32.5b 19.0-53.0 36CK' 1 530»bn = 25 Silt, loam, very fine sand, n = 18 Zn- 3.41» 2.67-4.20 18.7d' 10.5-29.5 Zn + 3.48» 2.85-4.14 34.9»b 25.0-63.0 310»d 600»b Fine sand, moraine n = 26 Zn- 3.1l ab 2.14-3.59 3.10» b 1.76-3.80 18.3» 7.5-38.0 280d Zn + 33.0 b 13.5-81.5 500 b Mull Zn- 2.91 b 2.46-3.63 25.5'" 18.5-33.5 Zn + 3.06b 2.35-3.83 39.0»b 31.0-48.5 360 d 590abn = 13 Peat n = 18 Zn- Zn + 2.89 b 2.88 b 1.86-3.77 1.99-3.77 28.4' 44.3» 9.0-55.0 21.0-62.0 410 630» 1 All means in the column were tested simultaneously. : Means of Zn- (superscripts c, d and e) and Zn+ (superscripts a and b) were tested separately. Table 40. Increase of Zn concentration upon application of Zn and utilization of added Zn. 1 Soil class n Increase of Zn concentration, mg kg-' Utilization of added Zn, % Mean Range Mean Range Clay 25 10.8 1-30 1.7b 0.5-4.8 Silt, loam, very fine sand 18 16.3 6-35 2.9» 1.7-4.2 Fine sand, moraine 26 14.5 4-53 2.1 ah 0.8-4.5 Mull 13 13.4 2-24.5 2.3 ab 0.3-3.9 Peat 18 15.8 4.5-28.5 2.2 ab -0.4-4.0 1 Means in the two columns were tested separately. lower (t = 4.072***) than that in the correspond- ing organogenic soils (27.1 mg kg" 1 ). In all soil classes, Zn application elevated Zn concentration of ryegrass significantly (t-values of the paired t- test not presented). The Zn concentration of the grass fertilized with Zn was lower (t = 3.276 )in mineral soils (34.0 mg kg" 1 ) than in organogenic soils (42.1 mg kg" 1 ). Zinc uptake correlated closely with the Zn concentration of the grass (r = 0.84 and r = 0.93 in pots grown with and withoutZn application, respectively), but there was no correla- tionbetween plant Zn concentration and dry matter yield. 4.2.3 Influence of soil characteristics on the response to applied Zn The average increase ofZn concentration caused by Zn application did not differ statistically from one soil class to another (Table 40), and the utilization of added Zn by the grass was low in all soil classes. The increase (mg kg" 1 ) in Zn concentration ofgrass correlated slightly negatively with the dry matter yield (r = 0.44 ), showing that the Zn concentra- tion of a smaller yield was more strongly increased than that of a larger one. In soils where grass of low Zn concentration was produced without added Zn, 240 Agric. Sei. Fin!. 2(1993) a high response to applied Zn was not necessarily measured, and even in soils producing grass of high Zn concentration a large response to applied Zn was occasionally observed. This resulted in a nonex- istent correlation(r = -0.06n s ) between Zn concen- tration of grass grown without applied Zn and the increase of Zn concentration. It can be seen in Figure 6 that in soils fertilized with Zn, soil pH had a more marked impact on plant Zn concentration as compared to soils not fertilized with Zn. In neutral and slightly acid soils the effect of added Zn on plant Zn concentration was much smaller than in the more acid soils. The relationship between soil properties and response of plant Zn concentration to applied Zn in mineral soils was studied in more detail by multiple regression ana- lyses. The results of soils 71 and 73 were not in- cluded in the tabulation, because soil 71 had an excessive ZnAc concentration and in soil 73 the increase of plant Zn concentration (+53 mg kg' 1 ) was much higher than in any other soil. The effect of added Zn on plant Zn concentration (y, mg kg' 1 ) decreased upon increasing soil pH which, accord- ing to the beta coefficients (Table 41), was rela- tively the most important independent variable.The equations below show that the increase of plant Zn concentration due to Zn application diminished with increasing soil pH at any level of native soil 3 -3ZnAc (mg dm ") or Znpy (mg dm ). On the other hand, at any pH the response was the greater the lower was the native ZnAc or Znpy in soil. Also the clay and organic C content (%) had a slightly negat- ive effect on the response. The regression equations for mineral soils (n = 68) were as follows: y = -7.58 pH - 0.070 Clay - 4.45 loge Znpy + 66.06 R 2 = 0.59** : (Equation 1) y = -8.23 pH - 0.77 C - 3.95 loge Zn Ac + 68.52 R 2 = 0.54**: (Equation 2) In organogenic soils the relationship between soil pH and plant Zn concentration was inconsist- ent. As a matter of fact, the grass of the lowest Zn concentration was produced in the two most acid organogenic soils (100, pH 3.8; 105, pH 4.1), which is a striking difference from mineral soils where acidity enhanced Zn uptake by the grass. In the two Fig. 6. Dependence of Zn concentration of ryegrass on soil pH in mineral soils fertilized with 10 mg Zn dm 3 (Zn+, symbol O) and those not fertilized with Zn (Zn., symbol □). 241 Agric. Sei. Fint. 2 (1993) Table 41. t-Values of regression coefficients and beta co- efficients ((3) of independentvariables in the regression equa- tions explaining the variation of increase in Zn concentra- tion upon Zn addition. Equation 1 and Equation 2: see text . Independent Equation 1 Equation 2 variable " " t P t P_ pH -8.374*** -0.69 -7.694*** -0.74 Clay -2.929** -0.24 log c Znpy -5.329*" -0.44 log, Zn Ac - -4.699*** -0.41 Organic C - - -1.929 1 -0.19 1 Significant at P = 0.058. grass grown in soils where native Znpy was easily available and strongly utilized responded strongly to added Zn and vice versa. The grass grown in three soils (77, 87 and 101) responded to added Zn markedly less than would be expected on the basis of the relative utilization of Znpy . In soils 77 and 101, the deviationbetween thereplicates was large, possibly contributing to the inconsistent results; soil 87 was rich in clay (69%), possibly reducing the availability of added Zn. Omission of the three soils increased the coefficient ofdetermination (R ) from 0.48 to 0.68. peat soils 100 and 105, the Zn concentrations of the grass not fertilized with Zn were as low as 11 and 9 mg kg’ 1 , respectively, and no higher than 21 mg kg’ 1 in grass fertilized with Zn. In organogenic soils the increase (mg kg’ 1 ) of plant Zn concentration was not explained by other soil properties, either. Instead, the response was dependent on the relative utilization (%) ofnative Znpy in the pot experiment (100 • Zn-uptake/Znpy) (Figure 7). In other words, 4.2.4 Response of ryegrass to applied Zn in soils poor in ZnAc The need for Zn fertilization is in Finland currently assessed on the basis of soil ZnAc- It is assumed that the need for Zn fertilization of a soil is the greater the less ZnAc is extracted from the soil. It might further be presumed that the greatest responses in plant Zn concentration would occur in soils poorest in ZnAc- According to the previous regression ana- lyses, a decrease in ZnAc indeed enhanced the re- sponse of plant Zn concentration to added Zn, but the regression equations did not accurately explain the variation of the response. Therefore the in- creases of Zn concentration were divided into quar- tiles (F25%) which were compared with the quar- tiles of soil ZnAc- Because, according to the present recommendations, Zn fertilization is most com- monly applied to soils poorest in ZnAc, the effect of Zn application on plant Zn concentration grown on these soils was studied with particular care. There were 19 mineral soils in the smallest quar- tile of ZnAc (ZnAc < 1.85 mg dm’3 . Table 42). Only in three of these mineral soils was there a strong response (the largest F 25%, quartile I) of plant Zn concentration to applied Zn. In the bulk of these mineral soils the increase of plant Zn concentration was smaller, placing them in the second or third quartile of response, but in none of the mineral soils concerned was the increase ofZn concentration of the grass very small (quartile IV). Within the group of these 19 mineral soils, the increase of plant Zn concentration did not correlate with soil ZnAc, but Fig. 7. Relationship) between relative utilization (%) of Zn extracted by pyrophosphate (Zn py ) and increase ofZn concen- tration of ryegrass upon application of 10 mg Zn dm 3 in 34 organogenic soils. 242 Agric. Sd. Fint. 2(1993) Table 42. Soil Zn Ac and pH in mineral and organogenic soils poorest in Zn Ac (ZnAc < 1.85 mg dnr 3). The soils are divided into groups according to quartiles (F25.;.) of the increase of Zn concentration of ryegrass when 10 mg Zn dm- 3 was added to the respective soil. Increase of Zn Soil ZnAc , mg dm- 1 pH concentration, mg kg-' ~~ ~ ~ ~ Mean Range Mean Range 2:18' Mineralsoils: 1.3 0.8-1.8 5.5 5.2-6.0 (Quartile I) 44, 52, 66 Organogenic soils: 1.3 0.6-1.8 5.2 4.8-5.6 83, 94, 97, 98, 103 13-17.5 1 Mineralsoils: 1.4 0.8-1.9 6.3 5.8-6.9 (Quartile II) 3, 13, 23, 28, 38, 45 48, 49, 54, 61, 63, 65 9-12.5 1 Mineralsoils: 1.6 1.5-1.9 6.0 5.4-6.5 (Quartile III) 12,37,41,64 Organogenic soils: 1.6 - 4.1 105 24.64.5 4.70.0024 5.4 NPK 20-4-8" 20.14.2 7.80.0031 5.3 NPK 17-6-124» 17.55.8 12.30.0062 5.3 NPK 14-9-10" 14.28.4 9.90.0047 5.1 KCI - - 50.50.0016 Triple superphosphate - 19.6 - 0.0144 The Finnish trade names of the commercial NPK fertilizers: » ’Vähäfosforinen Y-lannos’, 2 > ’Typpirikas Y-lannos I’, » ’Typpirikas Y-lannos 2’, 41 ’Typpirikas Y-lannos 3’, » ’Fosforirikas Y-lannos’ 0.30% on which the experimental design was based. Therefore, Zn application to the plots receiv- ing this fertilizer remained in reality slightly lower than intended. 5.1.2 Experiments with ryegrass and timothy a. Comparison ofZnfertilizers in a pot experiment Agronomic efficiency ofa few Zn fertilizers used in the field experiments was tested in a pot experiment with ryegrass in clay, fine sand and Carex peat (Appendix 6). The clay and fine sand were taken from the sites were the field experiments with timothy were carried out. Zinc sulphate mixed in the soil served as reference fertilizer. The other treatments resembled the alternatives available in practical farming of forage crops. The commercial fertilizer ’Sinkkilannos’ was mixed in the soil or was given as a topdressing,and the two Zn-contain- ing NPK fertilizers were surface-applied (Table 47). The two Zn rates were 2.7 (2.3 in NPK 18-3- 12) and 10 mg Zn dm'3 ofsoil. 3There was 7 dm of soil per pot and four replic- ates. At the beginning of the experiment, the same Table 47. Applications of Zn in the pot experiment. Treatment Zn, mg dm 3 1. Control, no Zn application 0 2. ZnS04 mixed in the soil 2.7 3. 'Sinkkilannos' mixed in the soil 2.7 4. 'Sinkkilannos' onto the soil 2.7 5. Zn in NPK 18-3-12 onto the soil 2.3 6. Zn in Coated NPK I onto the soil 2.7 7. ZnS04 mixed in the soil 10 8. 'Sinkkilannos' mixed in the soil 10 9. 'Sinkkilannos' onto the soil 10 quantities ofnutrients were applied as in the experi- ment reported in Section 4.3. The nutrient sources were compound NPK fertilizers and/or analytical grade chemicals. The pots to which Zn-containing NPK fertilizers were added obtained the bulk ofN, P and Kin these compound fertilizers. For the second crop, N, P and K were provided at the rate of 200, 50 and 200 mg dm’ , respectively. Nutrient solutions made of NH4NO3, KCI and KH2PO4 were pipetted onto the surface of all pots in four portions at a few days intervals. The pots were grown in a greenhouse and watered daily with 251 Agric. Sei. Finl. 2 (1993) deionized water. The grass yields were dried at 60°C and analyzed for Zn. h. Application ofZn fertilizers to timothy in thefield The objective of the 2-year experiments, performed in clay and fine sand soils (Appendix 6), was to study whether Zn concentration of timothy was equally affected by a single application of straight Zn fertilizers and applications of Zn incorporated in NPK fertilizers spread for each yield. The swards were sown in 1990 and harvested in 1991 and 1992. During the experiment, all plots, except the control, received 3 or 6 kg Zn ha" 1 (5.2 kg ha" 1 in NPK 18-3-12) as a single dose or as multiple smaller applications. Foliar application of Zn to the grow- ing sward was not made because Zn added that way can be adsorbed on the foliage without taking part in the reactions of the plant, which may cause ir- relevant results of plant analysis. The different Zn applications, presented in detail in Appendix 7, were as follows: 1) Single application of a straight Zn fertilizer (ZnSOaor ’Sinkkilannos’) at sowing (1990). 2) Single application of a straight Zn fertilizer (’Sinkkilannos’) onto the sward in spring of the first year of cropping (1991). 3) Applications of Zn-containing NPK fertiliz- ers (NPK 18-3-12, Coated NPK II or Coated NPK III) onto the sward in spring and after cutting the first crop in both years of harvest (1991 and 1992). When setting up the experiments, the fields were harrowed twice. Then, the granular Zn fertilizer ’Sinkkilannos’ was broadcast and ZnSOa, dis- solved in water, was sprayed on the appropriate plots. The NPK fertilization was applied with a fertilizer drill and timothy seeds were sown with a seed drill, simultaneously mixing ’Sinkkilannos' and ZnSOa in the soil. The next spring, granular ’Sinkkilannos’ was top-dressed on the assigned plots. In both experimental years, all plots received N, P and K fertilization as a top dressing at therates of 90, 32 and 64 kg ha" 1 , respectively. As men- tioned earlier, two of the NPK fertilizers contained added Zn. After the first cut in mid-June, when a few heads of timothy were emerging, NPK fertil- ization was applied again at the same rates and the swards were harvested for the second time later during the growing season. Owing to a drought in 1992, the experiment in clay soil was irrigated on June 30 (28 mm ofwater) and the latter cut of both experiments took place as late as the end of Septem- ber. In addition to the actual Zn fertilization, all plots received 19 g Zn ha" 1 in the NPK fertilizer when the experiments were established. During the years of harvest, the plots received a maximum of 130 g Zn ha" 1 as impurities of NPK fertilization. This quantity corresponds to 5% of the smaller application of 3kg Zn ha" 1 and can be considered negligible. The stand was cut with a forage harvester. The yield of each plot was collected in a glass fibre box attached to the harvester. The plant samples, to be analyzed for Zn, N and moisture, were taken just before the actual harvesting. The samples, com- posed oftwo subsamples of0.25 m from each plot, were collected by hand using stainless steel scissors and weighed together with the harvested yield of the respective plot. Soil samples were taken from each plot and analyzed for pH and ZnAc in the beginning and at the end of the experiment. 5.1.3 Field experiments with barley a. Comparison ofZnfertilizers The objective of the three 3-year field experiments carried out in 1990 through 1992 on clay, fine sand and mull soils (Appendix 6) was to establish whether Zn concentration ofbarley can be elevated with moderate Zn applications given in different fertilizers and whether a single application at the beginning of the experiments differs in efficiency from smaller annual applications. During the ex- periment, all plots, except the control, received 5.4 kg Zn ha" 1 (4.8 kg ha" 1 in NPK 18-3-12) either as a single application at the beginning or as three annual applications of 1.8 kg Zn ha" 1 (4 x 1.6 kg ha" 1 in NPK 18-3-12).The treatments, presented in detail in Appendix 8, were as follows: 252 Agric. Sei. Fint. 2(1993) 1) Single application of a straight Zn fertilizer (ZnSO4 or ’Sinkkilannos’) in the first spring of the trials. 2) Annual doses of Zn incorporated in granular NPK fertilizers (NPK 18-3-12 or Coated NPK I). 3) Annual doses of Na2Zn-EDTA sprayed each spring onto the soil. 4) Annual doses of Na2Zn-EDTA sprayed on the foliage. Each spring the soil was harrowed twice. After harrowing, the granular Zn fertilizer (’Sinkkilan- nos’) was broadcast (in 1990 only), and ZnSOa (in 1990 only) and Na2Zn-EDTA (annually) were sprayed on the appropriate plots as water solutions. These fertilizers were mixed in the soil with a com- bined seed and fertilizer drill in connection with sowing and application of the NPK fertilizers. The granular NPK fertilizers, including added Zn in two fertilizers, were applied by the placement method. At the Feekes 5 growth stage (Large 1954), when the plants had usually reached the height of 10 - 15 cm, water solution of Na2Zn- EDTA was sprayed on the assigned plots. In 1992, the experiment on clay soil was irrigated with 13 mm of water on July 1. In addition to the actual Zn fertilization, the experiments on clay and fine sand received 37 gZn ha’ 1 as impurities of other fertiliz- ers during three years, except the plot fertilized with the NPK 18-3-12 and Coated NPK I. In mull soil, the corresponding quantity was 120 g Zn ha’ 1 , owing to the larger Zn concentration of the NPK fertilizers used in that experiment. The grain yield, harvested with an experimental harvester (Hege 125), was weighed and analyzed for moisture and Zn. Also the straw was analyzed for Zn and moisture. The straw yield was weighed in the last two experimental years. h. Application ofdifferent Zn rates The objective of the two 2-year field experiments with barley was to investigate the effect of high Zn rates (15 and 30 kg ha’ 1 ) on the Zn concentration of barley at different growth stages. The experiments, presented in detail in Appendix 9, were carried out in the same fine sand and clay soil (Appendix 6) in which the different Zn fertilizers were experi- mented. After harrowing in the first spring (1991) of the experiment, powdery ZnSOa was applied by hand at therate of 0, 15 or 30 kg Zn ha" 1 and mixed in the soil by harrowing for one more time. The NPK fertilizer was applied with the combined seed and fertilizer drill to supply N, P and K at therates of 110, 22 and 44 kg ha' 1 , respectively. In the second spring (1992), no Zn was added and the results of the second experimental year thus reflect the residual effect of the Zn fertilization. The quantity of Zn as impurity in the NPK fertilizer during the two years was 34 g ha' 1. In 1992, the experiment on clay soil was irrigated with 20 mm of water on July 1. The plant samples were collected four times dur- ing the growing season from each plot by cutting the plants each time from two areas of0.25 m . The stand was sampled at the beginning of tillering (Feekes 2), at the end of tillering (Feekes 5), at the end offlowering (Feekes 10.5) and at maturity. The number ofdays from sowing to these growth stages was 38 - 39 days, 50 - 52 days, 69 -70 days and 104 days, respectively, in 1991 and 26 - 28 days, 40 - 43 days, 61 days and 91-96 days, respectively, in 1992. The plant samples were dried and weighed. The grains were removed from the ears of mature plants by hand and the remnants of the ears were combined with the straw. The plant samples were analyzed for Zn; the grains and straw were weighed and analyzed separately. At the end of the experi- ments, a composite soil sample of each plot was analyzed for ZnAc. 5.1.4 Weather Precipitation and temperature were measured at the Kotkaniemi Experimental Farm. The three growing seasons in which the field experiments were con- ducted differed strongly in weather of the early summer. In 1990 and 1992,May and June were dry and warm (Table 48). In 1992, the drought con- tinued until the end of July, resulting in a shortage of water especially in the experiments on the clay 253 Agric. Sei. Fin!. 2 (1993) Table 48. Monthly mean temperatures and precipitations at the Kotkaniemi Experimental Farm during the months of growing seasons of the experimental years and means over a period of 18 years. Month Temperature, °C Precipitation, mm 1990 1991 1992 1974-91 1990 1991 1992 1974-91 May 11.98.5 11.410.5 27 27 16 33 June 16.0 13.8 16.114.8 14 58 16 44 July 16.019.2 19.116.6 88 41 32 68 August 16.516.7 16.615.0 49 98 90 76 September 9.210.5 13.29.6 82 53 61 65 Table 49. Concentration of Zn in ryegrass. I and II refer to the first and second crop, respectively. l Treatment Zn added mg dnr3 Zn concentration (mg kg l) of grass grown in Fine sand Carex peat I II Clay I II 1 II Control 0 52.9 C 51.6“ 40.7“ 38.8' 39.8'“ 31.0 f ZnS04 2.7 66.6 b 60.8 cd 65.l b 57.6 d 56.0C 72.3bc 51.8C 51.9d 54.4C 55.l d 45.7»' 42.5“' 42.3'“ 42.9“' 41.2“ 44.2'“ 39.8“ 42.0“' 39.3“ 43.3'“' 45.4» 38.4“' 38.2'“ 37.5' 37.4“ 45.8»' 38.6'“ 35.4' f 35.7“ 35.7' ’Sinkkilannos’ 2.7 ’Sinkkilannos’, s.a. 2 NPK 18-3-12, s.a. 2 Coated NPK I, s.a.2 2.7 2.3 2.7 ZnS04 10 84.7» 73.5 b 52.7» 51.3» 46.1»' 47.8»' 46.8» 58.8» 56.7» 48.0» 52.2» 42.5'“ 43.2»' 66.5» ’Sinkkilannos’ 10 85.6“ 75.O b 65.0» 88.5“ 6.912.2 ’Sinkkilannos’, s.a. 2 10 HSD0 05 4.14.8 5.2 4.4 1 Results of each soil and crop were tested separately. 2 s.a. = surface-applied soil. Inversely, in 1991 especially June was cooler and rainier than normal. 5.2 Comparison of Zn fertilizers, Zn rates and application practices with grass crops 5.2.1 Effect of Zn fertilizers on ryegrass in a pol experiment Zinc application did not affect ryegrass yields in the pot experiment, and therefore only the mean yields obtainedfrom each soil (g per pot) are presented: Crop II 20.1 Crop I 13.7Clay Fine sand Carex peat 18.19.9 16.612.2 At the lower rate (2.7 or 2.3 mg Zn dm'3 ), ZnSCU elevated Zn concentration of the first ryegrass crop in all soils (Table 49), but only in fine sandalso the granular ’Sinkkilannos’, mixed in the soil, had a significant effect. In the second crop, the effect of the fertilizers was different; granular ’Sinkkilan- nos’ elevated plant Zn concentration relatively more efficiently than in the first crop, probably owing to a longer time available for the dissolution of the granules. In the second crop, the surface-ap- plied ’Sinkkilannos’ elevated plant Zn concentra- 254 Agric. Sei. Fint. 2 (1993) lion in all soils at least as effectively as ZnSOa mixed in the soil. Actually, surface-applied ’Sink- kilannos’ was the only fertilizer which elevated plant Zn concentration significantly at the lower application rate in the second crop in fine sand and Carex peat. The only significant effect of the two Zn-containing NPK fertilizers on plant Zn concen- tration was observed in the second crop in clay with the coated NPK I. At the higher application rate (10 mg dm'3) the increase of plant Zn concentration was substan- tially higher. In fine sand, ’Sinkkilannos’ mixed in the soil was equal to ZnSC>4 in efficiency in both crops, but in the first crop in Carex peat and in the second crop in clay, ZnSOa was more efficient. Also at the higher Zn rate top-dressing of ’Sink- kilannos’ was a less effective way of application than was mixing in the soil in the first crop in fine sandand clay soils. In the second crop the contrary was observed: topdressing of ’Sinkkilannos’ was the most effective way of Zn application in all soils. The efficiency of the surface-application of ’Sink- kilannos’ in the second yield was also emphasized when comparing the results obtained at the two Zn rates. Surface-applied ’Sinkkilannos’ at the lower rate elevated Zn concentration of ryegrass as much as did the higher rate of ’Sinkkilannos’ mixed in the soil. Despite substantial increases in Zn concentra- tion of ryegrass, the utilization of added Zn re- mainedat 1 - 2% in all soils. 5.2.2 Effect of Zn fertilizers on timothy in the field All the four timothy yields (Table 50) obtained from the fine sand field during the two growing seasons were ofnormal size. Owing to poor growth, only two of the four blocks could be harvested in clay soil in the first experimental year and the first yields remained small also in the harvested blocks. Later, the yields obtainedfrom the clay soil were of the same magnitude as those from the fine sand. The results concerning the clay soil represent the yield of those two blocks harvested in both years. Dry matter yields did not respond to Zn applica- tions. Table 50. Dry matter yields and raw protein (6.25 • N) con- tents of timothy. I and II refer to the first and second crop in the respective growing season. Soil Successive crop 1/1991 11/1991 1/1992 11/1992 Dry matter, kg ha 0 Clay 1115 4054 3695 2350 Fine sand 2568 3935 4320 2100 Raw protein, "la Clay 14.3 14.5 15.418.2 Fine sand 15.0 14.6 15.1 18.3 The results of Zn concentration and uptake were tested with the analysis of variance using Zn fertil- ization and the crop (1/1991, 11/1991, 1/1992, 11/1992) as the two criteria of classification. The results of the blocks served as replicates. The F- values in Table 51 suggest that in both experiments the systematic differences between the Zn concen- trations of the four crops were at least as significant as those caused by the different fertilization treat- ments. In clay soil, Zn concentration of timothy varied in a rather narrow range in the four crops of each treatment (Table 51). In fine sand, theranges were slightly wider mainly because the Zn concentra- tions of crop 11/1992 were substantially higher than those of the other crops. In neither experiment did the lower Zn rate (3 kg ha’ 1 ) elevate the mean Zn concentration of timothy significantly. At the higher Zn rate (6 kg ha’ 1 ) ’Sinkkilannos’, applied by mixing in the soil or by top-dressing, elevated Zn concentration of timothy significantly in both soils. In addition, Zn concentration of the grass fertilized with ZnSOa (6 kg Zn ha' 1 ) or with the coated NPK 111 (6 kg Zn ha' 1 ) differed significantly from the control in clay soil. ’Sinkkilannos’ mixed in the soil seemed to be slightly more effective at both levels than ZnSOa alone, but the difference between these two fertilizers was not significant. A decrease in the effectiveness of Zn application during the experiments was not detected. As a mat- ter of fact, the greatest increases in Zn concentra- 255 Agric. Sei. Finl. 2 (1993) Table 51. Zinc concentration and uptake of timothy in two 2-year experiments as means of the four crops. Treatment Zn rate kg ha-' Zn concentration, mg kg 1 Zn uptake, g ha Mean Range Mean Clay 1. Control 0 28.0C 25-31 80 2. ZnS04 3 3 3 30. 1 1 * 27-34 85 3. ’Sinkkilannos 32.4>bc 29-34 86 4. ’Sinkkilannos’, s.a. 1 5. Coated NPK 11, s.a. 1 31.9** 27-37 87 4x0.75 29.6bc 25-32 79 6. ZnS04 6 6 6 33.6ab 31-37 92 7. ’Sinkkilannos’ 35.6“ 33-38 98 8. ’Sinkkilannos’, s.a. 1 9. NPK 18-3-12, s.a. 1 10. Coated NPK 111, s.a. 1 36.5 a 36-38 100 4x 1.3 4x 1.5 29.5bc 27-33 82 34.1ab 31-37 99 HSDoos (fertilizations) F (fertilizations) 5.3 27 5.612’*’ 8.802’” 1.875" ‘ F (crops) 152.840’” -- Fine sand 32-40I. Control 0 34.9cd 112.1k 2. ZnS04 3 3 3 35.9*d 40.0»* 38.9*d 34. l d 30-41 121,bc 3. ’Sinkkilannos 36-48 122abc 4. ’Sinkkilannos’, s.a. 1 5. Coated NPK 11, s.a. 1 34-46 136ab 4x0.75 31-40 100 6. ZnS04 6 6 37.6*d 41.0»» 44.6» 34-44 124* 7. ’Sinkkilannos’ 36-47 126abc 8. ’Sinkkilannos’, s.a. 1 9. NPK 18-3-12, s.a. 1 10. Coated NPK 111, s.a. 1 6 37-55 140“ 4x 1.3 4x 1.5 34.3d 35.2cd 30-38 103bc 108abc 35.5 2.937” 35.745”' 32-41 HSD0 os (fertilizations) 5.3 9.193*” 41.960*" F (fertilizations) F (crops) 1 s.a. = surface application tion of grass occurred in the last crop harvested. The effect of a given Zn rate was similar in both soils. As the mean of the two experiments, ’Sink- kilannos’ increased plant Zn concentration by 4.4 and 8.5 mg kg' 1 at the application rate of 3 and 6kg Zn ha' 1 , respectively, corresponding to an increase of 1.4 mg kg' 1 for each kilogram of Zn applied. Cumulative Zn uptake in the four crops (4 x the means in Table 51) was 317 - 399 g ha' 1 and 400 - 561 g ha' 1 in clay and fine sand, respectively. Some treatments seemed to increase Zn uptake by the crop but in neither soil did any of the treatments differ significantly from the control. The apparent utilization of fertilizer Zn corresponded to 0.8 - 1.5% of added Zn in the treatments where the Zn concentration of the grass was significantly ele- vated. Soil analyses carried out at the end of the experi- ments showed that Zn applications yielded slightly elevated ZnAc in clay (F = 12.584 ). Owing to a large variation of the results in fine sand, the influ- ence of Zn application on ZnAc was not significant (F = 1,742n 's ‘). Surface-application of granular Zn containing fertilizers may have caused an uneven distributionof Zn in the soil, possibly resulting in a 256 Agric. Sei. Fin!. 2 (1993) failure of representative sampling. The means of ZnAc (mg dm’3 ) at the various levels of added Zn, tested separately in clay and fine sand, were as follows: Zn, kg ha’ 1 0 Clay 1.2b 1.4b 2.0a Fine sand 2.8 3 6 3.3 3.5 Table 52. Grain and straw yield (kg ha 1) of barley in three field experiments. Yield Year Yield (kg ha 1) obtained from Clay Mull Fine sand Grain 1 1990 4597 6361 6996 1991 5222 5604 6414 1992 1790 7051 5514 Straw 1991 2456 3435 3236 1992 660 2782 3040 1 Grain yields are presented at the moisture of 15%. 5.3 Comparison of Zn fertilizers, Zn rates and application practices with barley 5.3.1 Different fertilizers as Zn sources for barley The growth of barley was ample in 1990 and 1991, but in 1992 the yields were reduced in clay by the drought (Table 52). In none of the experiments were grain or straw yields affected by Zn fertiliza- tion. Zinc concentration ofgrain and straw (Table 53) was the highest in mull which had the lowest pH and highest content of ZnAc- Inversely, the lowest concentrations occurred in barley grown in fine sand which had the highest pH and was poorest in ZnAc- Zinc concentration of grain was, with few exceptions, at least twice the Zn concentration of the straw. Foliar application of Na2Zn-EDTA ele- vated Zn concentration of grain and straw signific- antly in all experiments. The increase in Zn con- centration of grain was 4.3, 3.7 and 4.5 mg kg' 1 in clay, mull and fine sand, respectively. In mull and fine sand, none of the soil-applied Zn fertilizers affected Zn concentration of grain or straw. On the contrary, in clay all soil-applied Zn fertilizers, ex- cept Na2Zn-EDTA mixed in the soil, elevated Zn concentration of the grain and the two Zn-contain- ing NPK fertilizers increased Zn concentration of the straw. No systematic difference could be de- tected in the effect of Zn fertilizers applied in the soil annually and that applied only at the beginning of the experiment. It shouldbe pointed out that the Zn concentration of the crop did not correlate with Table 53. Mean Zn concentration of barley grains and straw in three 3-year field experiments in which different Zn fertilizers were applied at the rate of 5.4 kg ha* 1 (4.8 kg ha 1 in NPK 18-3-12).' Zn concentration (mg kg ') in yield obtained from Treatment Clay Mull Fine sand Grain Control 29.3b 39.4b 17.6b ZnS042 33,3 a 39.4 b 18.3b ’Sinkkilannos’ 2 33.8a 40.3b 18.6b Na2 Zn-EDTA in soil 3 32.9“ b 39.2 b 18.2b NPK 18-3-123 34.2“ 39.6 b 19.1“l34.2“ 39.6b 19.l ab Coated NPK I 3 34.5“ 39.6» 16.5» Na2 Zn-EDTA, foliar3 33.6“ 43.1“ 22.1“ HSDo.o, 4.0 2.9 3.5 F (treatments) 3.504” 4.086” 4.568*” F (years) 37.251’*’ 10.783’’’ 2.849" * Straw Control 11.0b 17.9» 5.6» ZnS04 2 14.5a» 15.8» 6.8a » ’Sinkkilannos’ 2 12.9a» 17.6» 6.2» Na2Zn-EDTA in soil 3 12.9*» 18.7» 6.0» NPK 18-3-123 15.2* 18.7» 7.1*115.2“ 18.7» 7.1*» Coated NPK I 3 16.0“ 17.5» 6.2» Na2Zn-EDTA, foliar3 16.6“ 25.9“ 9.8“ HSDo.o, 4.1 6.1 3.3 F (treatments) 4.189” 5.189*” 3.425” F (years) 7.344*” 71.063”* 7.194’” 1 Results of grain and straw were tested separately in each soil. 2 Applied only at the beginning of the experiment. 3 Applied each year at the rate of 1.8 kg Zn ha*' (1.6 kg ha ' in NPK 18-3-12). dry matter yield. For example, in clay the highest yield in 1991 and the lowest one in 1992 had similar Zn concentrations in grain (mean of all plots 36.1 257 Agric. Sei. Finl. 2 (1993) and 34.2 mg kg' 1 in 1991 and 1992,respectively) and straw (12.4 and 14.4 mg kg' 1 , respectively). In the three years, Zn concentration of grain of the control plots varied within a narrow range (3 mg kg' 1 in clay and mull, 1 mg kg' 1 in fine sand). In clay there was substantial annual variation in Zn concentration of grain in the plots fertilized with Zn. In the first experimental year, Zn concentration was below 30 mg kg' 1 in all treatments, while in the two following years the average concentrations of the different treatments ranged from 32 to 38 mg kg' 1 . The annual variation of straw Zn concentra- tion was by far the greatest in mull where the means were 27.4, I l.6and 14.2mg kg' 1 in 1990, 1991 and 1992, respectively, in plots other than those of Na2Zn-EDTA application. In clay and fine sand the annual variation in Zn concentration of straw was less marked. The mean annual Zn uptake by barley grains was 89, 212 and 94 g ha’ 1 in the control plots of clay, mull and fine sand, respectively. In clay, all Zn fertilizers slightly increased Zn uptake but only the Coated NPKI gave rise to a significant increase (24 g ha' 1 , +27%). In fine sand, foliar application of NaiZn-EDTA elevated Zn uptake significantly (by 23 g ha' 1 , +24%); utilizationof foliar-applied Zn in grain was 1.3%, 0.6% and 0.8% in clay, mull and fine sand, respectively. Mean annual Zn uptake by the straw in the control plots was 15, 42 and 17 g ha' 1 in clay, mulland fine sand, respectively. Foliar application of NaiZn-EDTA increased the quantity of Zn harvested in the straw by 12,21and 18 g ha’ 1 in clay, mull and fine sand, respectively, corres- ponding to 0.7 - 1.1% of the foliar-applied Zn. 5.3.2 Plant Zn concentration as affected by different Zn rates Zinc application of 15 or 30 kg Zn ha’ 1 did not affect the dry matter yields at any growth stage, and only the means of the dry matter produced at different growth stages are presented (Table 54). There was a decreasing trend in Zn concentrationof vegetative plant material in the course of the grow- ing season (Table 55). In 1991, Zn concentrations in the samples taken at the Feekes 2 and 5 growth stages were higher than in the vegetative parts of the plants at later growth stages in both soils. In 1992, the samples taken at Feekes 2 growth stage had a significantly higher Zn concentration than the vegetative parts of the later growth stages. The higher Zn concentration in grain, as compared to that of straw, suggests an effective translocation of Zn from the vegetativeparts. The phenomenon was pronounced in fine sand where Zn concentrationof the straw was extremely low in 1992. Even though ZnAc was of the same magnitude in both soils, Zn concentration of barley at any growth stage was higher in clay soil than in fine sand which had a higher pH. In clay, Zn application elevated Zn concentration of barley only in the first experimental year (F = 12.503 ) and showed no residual effect in the second year. In fine sand where Zn application of 5.4 kg ha' 1 to the soil (see Section 5.3.1) did not affect Zn concentrationofbarley, the higher rates in the present experiment had a significant effect in the first year (F = 19.820 ) and there was an increase in plant Zn concentration (F = 4.107 ) Table 54. Dry matter yields (kg ha 1) produced by barley at different growth stages in two field experiments. Soil and year Growth stage Feekes 2 Feekes 5 Feekes 10.5 Grain 1 Straw 1 Clay: 1991 655 3579 5419 1992 587 1201 3113 2346 1757 Fine sand: 1991 1942 4399 8146 5483 4814 1992 1012 3058 7420 5861 4391 1 The grain and straw samples of 1991 from the experiment on the clay soil were destroyed by fire. 258 Agric. Sei. Finl. 2 (1993) Table 55. Zinc concentration and uptake of barley at different growth stages in two field experiments. I, II and 111 refer to the plant samples taken at Feekes 2, 5 and 10.5 growth stages, respectively. l Soil Zn application, Zn (mg kg 1) at various growth stages Zn uptake (g ha ') and year kg ha-' ~ ~ ~ ; " at maturity2 I II 111 Grain Straw Clay 1991 0 37.8» 31.8 b 18.3 - - 106! 15 52.9» 49.0»» 25.0 - - 1322 30 58.3» 53.3» 25.3 - - 1392 HSD0 .„, 11.820.9 8.3 51 Clay 1992 0 29.223.3 21.632.0 14.1 98 15 27.723.8 21.336.8 15.9 110 30 28.324.5 21.236.0 16.6 118 HSD005 16.05.0 4.85.6 6.0 61 Fine sand 0 27.4" 20.38.1 14.6" 4.7 101" 1991 15 31.9* 37.010.5 19.6» 8.1 142»b 30 35.6» 43.511.3 21.8» 11.4 185» HSD005 5.140.3 3.54.6 7.8 54 Fine sand 0 21.915.5 10.616.9 2.6 113 1992 15 22.516.7 13.018.1 3.2 118 30 22.918.3 13.419.9 3.7 128 HSD005 7.03.7 6.08.0 1.7 24 1 Zinc concentration and uptake were tested separately in each soil, each year and growth stage. 2 In 1991, Zn uptake in the clay soils refers to the sampling at Feekes 10.5 growth stage. also in the second year. In neither of the soils did Zn concentration of the plants at Zn rate 15 kg ha" 1 differfrom that at Zn rate 30kg ha" 1 . The utilization of applied Zn was extremely low, 0.2 - 0.3%. When the plant Zn concentrations were compared separ- ately at each sampling (Table 55), the differences between the Zn rates were not always statistically significant even in the first year, owing to large variation in the Zn concentrationof plants fertilized with Zn. The influence of Zn application on Zn concentration of barley was greater in the early growth stages than later in the growing season (Feekes 10.5), reflecting the accumulation of dry matter and suggesting that Zn was taken up at the early part of the growing season. Soil analyses at the end of the experiments showed that the effect of the application of high rates of ZnSCH on soil ZnAc was rather small and statistically insignificant both in clay (F= 1,554n s ) and in fine sand (F = 2.298n s ). The means ofZnAc (mg dm’ 1 ) at the different levels ofadded Zn, tested separately in clay and fine sand, were as follows: Zn, kg ha" Clay Fine sand 0 3.51.9 15 2.92.5 30 6.03.8 5.4 Discussion The status of ZnAc of the mineral soils where the field experiments were carried out was far below the average ZnAc of cultivated soils of Finland (Sippola and Tares 1978 and unpublished data of Soil Analysis Service Ltd.). In spite of the rather low ZnAc concentration, timothy did not show any signs of Zn deficiency and had a Zn concentration similar to the mean value in samples collected from various parts of Finland (KÄHÄRI and Nissinen 1978). Also Zn concentration of barley grains was well beyond the deficiency level in clay and espe- cially in mull where the abundant ZnAc reserves in the subsoil may have contributed to the high Zn 259 Agric. Sei. Fin!. 2 (1993) 2 concentration in barley grains. The sufficient sup- ply of Zn from soil reserves explains the absent response of timothy and barley yields to added Zn In the control plots of fine sand, Zn concentration of barley grains was below 20 mg kg’ 1 but the growth was probably not limited by Zn deficiency because the yield was not increased by Zn applica- tions. Moreover, the higher Zn concentration ear- lier in the growing season suggests that Zn supply for barley was at a very sufficient level during the intensive growth also in the fine sand. The efficiency of ZnSOa to increase Zn concen- tration of timothy was similar to that observed in other field experiments carried out with forage grasses in acid mineral soils. For example, in two mineral soils (pH 5.6 and 5.8) in New Zealand (McLaren et al. 1991)an application of4.6 kg ha’ 1 as ZnSOa increased Zn concentrationof herbage by 8.9 mg kg' 1 . In the experiments of Jaakkola and Vogt (1978) in Finland the increase ofZn concen- tration of hay in the first experimental year corres- ponded to 1.3 mg kg' 1 for each kilogram of Zn applied, which agrees with the results of the present study. The response of plant Zn concentration is, however, strongly dependent on soil charac- teristics. The studies of Urvas (1986, 1992) on Zn fertilization of timothy show that the efficiency of fertilizer Zn can be much higher in strongly acid peat soil, and even a small application of Zn (0.55 kg ha’ 1 ) may elevate plant Zn concentration significantly. The low or absent response ofZn concentration of barley grains to 4.8 or 5.4kg Zn ha’ 1 applied to soil is in agreement with other Finnish field experi- ments where small rates (1.75 kg ha’ 1 ) of Zn have been given (Jaakkola and Vogt 1978, Syvä- lahti and Korkman 1978). A higher Zn applica- tion (15 and 30 kg ha' 1 ) elevated Zn concentration of barley significantly in fine sand, but even then Zn concentration of grain remained around 20 mg kg’ 1, reflecting the poor availability of Zn in neutral soil. However, the response was of the same level as has been observed in the neutral and slightly acid mineral soils of Norway and Canada where 50 and 20 kg Zn ha’ 1 , respectively, were applied to barley (Myhr 1988, Gupta 1989). The drought in 1992may partly explain the small residual effect of the high Zn rates (15 and 30 kg ha' 1 ) on barley. In the first year of the experiment (1991) there was plenty of rain in May and June, and the roots of barley were probably active in the plough layer, resulting in the observed response to applied Zn. Owingto the drought in the second year (1992) the plough layer was dry and plant roots were able to take up nutrients from thatpart of the soil less effectively. In 1992, the roots probably grew to a greater extent into the deeper soil layers where they were no more in contact with the ap- plied Zn. This hypothesis is supported by the find- ings made in Canada by Dwyer et al. (1988) ac- cording to which the maximum rooting depth of barley and the quantity of roots in the deeper soil layers increase when there is shortage of water in the surface soil. The hypothesis does not, however, explain why there was some response by barley to soil-applied Zn also in 1992 in clay soil in the other experiment where the different Zn fertilizers were tested (Section 5.3.1). Granulation and spot-placement commonly de- crease the agronomic efficiency ofZnSOa added to neutral and calcareous soils (Brown and Krantz 1966, Allen and Terman 1967, Mortvedt and Giordano 1969a). However, in the present study, carried out in acid soils, the granulated ’Sinkkilan- nos’ mixed into the soil elevated plant Zn concen- tration at the same rate as did ZnSOa. In the granu- lated product, ZnSOa is incorporated in gypsum, and Zn cations seem to be readily released from the matrix into the soil solution. Also the top-dressed ’Sinkkilannos’ increased Zn concentration of grass in the field and pot experiments at least as effect- ively as did the fertilizer mixed in the soil. Avail- ability of Zn in granular fertilizers added onto the soil surface requires that Zn be dissolved from the granule and further to move into the soil and to get into contact with active plant roots. The rains in the early summer of 1991 right after broadcasting the fertilizers or the daily watering in the pot experi- ment probably resulted in an effective disintegra- tion of the granules of’Sinkkilannos’ and enhanced the penetration of Zn into theroot zone. In a short- term pot experiment, top-dressing retarded the fer- tilizer effect of ’Sinkkilannos’, but in the field there was evidently enough time for the surface-applied 260 Agric. Sei. Fint. 2 (1993) granules of ’Sinkkilannos’ to dissolve before the first harvest, and consequently there was no differ- ence between the application methods. The negligible agronomic efficiency of Zn con- tained in NPK fertilizers cannot solely be attributed to the granular form of the fertilizers because the granular ’Sinkkilannos’ did elevate plant Zn con- centration in the very same experiments. The low efficiency is rather due to the chemical reactions occurring in the fertilizer between Zn and the other components. During the manufacturing process of the present NPK fertilizers the acid orthophosphate slurry is ammoniated (Kivioja 1987), resulting in an elevation of pH. The accompanying decrease in the water-solubility and plant-availability of Zn added to the fertilizer as ZnSOa (Mortvedt 1968, Mortvedt and Giordano 1969b) is due to the precipitation of insoluble Zn compounds (e.g. Zn phosphates, Zn hydroxides) in the fertilizer grain (Terman et al. 1966, Allen and Terman 1967, Mortvedt and Giordano 1969a). According to Mortvedt (1968), above pH 5 the availability of Zn in ammoniated orthophosphate fertilizers is less than 20% of what is observed when ZnSCH is ap- plied separately or incorporated in unammoniated (pH 3) orthophosphate fertilizer. The pH of the present NPK fertilizers ranged between 5.0 and 5.4, suggesting a low water-solubility ofZn in the fertil- izer. The present field and pot experiments showed that the sparingly soluble Zn compounds are not necessarily dissolved during short-term experi- ments even in acid soils, resulting in an inconsistent fertilizer effect. Because the NPK fertilizers coated with ZnSO4 had an equally low availability of Zn, it is likely that ionic activities also in the vicinity of the fertilizer granule exceed the solubility products of sparingly soluble Zn compounds. The current results disagree with those of Sil- lanpää (1990) who applied Zn-containing NPK fertilizers to barley in ten field experiments in Fin- land. In those experiments, high Zn rate (11.6 kg ha' 1) and low soil pH (CaCb-pH 4.2 - 5.5) probably facilitated the mean increase of 8 mg kg' 1 in grain Zn concentration. Moreover, in the fertilizers of Sillanpää, part of Zn (2 kg ha' 1 ) had been added as Zn-EDTA. According to Mortvedt and Gior- dano (1969a), the plant-availability ofZn added as Zn-EDTA in macronutrient fertilizers is not re- duced as much as that ofZnSO4. Increased Zn concentration of barley straw by foliar sprays of Na2Zn-EDTA can at least partly be caused by the adsorption offoliar-applied Zn on the surfaces ofplant leaves. Therefore the increased Zn concentrationof straw by this treatment must not be considered an indication of high fertilizer effi- ciency. Because NazZn-EDTA was sprayed at an early growth stage before there was any shoot or ear in the crop, the increase of grain Zn concentration can be attributed to the introduction of applied Zn into the physiological reactions of the plant. How- ever, soil pH strongly dominated the grain Zn con- centration also in this treatment. In some studies application of Zn in a chelated form to neutral or calcareous soils has been at least twice as effective as application of ZnSOa (Mortvedt and Gior- dano 1969a, Boawn 1973, Hergert et al. 1984). The difference between the two sources has not been significant in acid soils (Hergert et al. 1984) and not always even in neutral soils (SCHNAP- pinger et al. 1972). Also in the present study, the soil-applied Na2Zn-EDTA failed to increase plant Zn concentration, which shows that the observed effect of foliar application of NazZn-EDTA can be attributed primarily to the application method rather than to the chelated form ofZn. This conclu- sion is supported indirectly by theresults ofPATER- SON et al. (1991) who elevated Zn concentration of barley grains with foliar sprays of ZnSOa, while the application of ZnSO4 to the soil was withouteffect. Further, it needs to be pointed out that foliar appli- cation of Na2Zn-EDTA was the only treatment in- creasing Zn concentration of barley grain in fine sand where insufficient Zn supply to barley may have been approached. 261 Agric. Sei. Finl. 2 (1993) 6 GENERAL DISCUSSION AND CONCLUSIONS in spite of generally sufficientZn reserves for plant growth the present material contained a few soils poor in Zn. Even though worldwide zinc deficiency is commonly connected to calcareous soils, low plant-availability of Zn may occur also in slightly acid and neutral mineral soils of Finland. More- over, the soil testing method applied in Finland (AAAc-EDTA, pH 4.65) seems to overestimate the Zn supply to plants in these soils. However, the soils with the scarcest reserves were among Carex peat and Ligno Carexpeat soils, which were poor in Zn also according to international comparisons. Owing to the small number of organogenic soils in the present material, it is not possible to draw con- clusions on the geographic occurrence of Zn defi- ciency in Finland even though cultivated peat soils are the most common in the northern parts of the country. Peat soils constitute less than 10% of the cultivated area of Finland (Kurki 1982), but they are not all poor in Zn. Only 1.5% of samples ana- lyzed for ZnAc in soil testing in 1986 - 1988 con- tained ZnAc less than 1.0 mg dm’ (unpublished data of Soil Analysis Service Ltd.) and were rated poor in Zn according to the current interpretation (Viljavuuspalvelu 1992). The present results as well as those of Urvas (1985, 1990) suggest that yield response to applied Zn is hardly observed in short-term experiments even in these soils. Conse- quently, a ZnAc concentrationbelow 1.0mg dm" in the soil does not necessarily indicate insufficient Zn supply to the crop. In accordance with the results of soil analyses and pot experiments, yield increases owing to Zn fertilization have not been detected in the field in Finland. Therefore, Zn fertilization in the great majority of cultivated soils ofFinland is justified by the possible elevation of Zn concentra- tion of the crop. It seems feasible that in the poorest peat soils Zn reserves can be exhausted over time in intensive grassland cultivation. In the studies of Sillanpää and Rinne (1975) the quantity of Zn harvested in three cuttings ofsilage grass amounted to 280 g ha" 1 at the annual N fertilizer level of300 kg ha’ 1. At this rate, the uptake ofZn in 10years amounts to 2.8kg 1 3ha , or 1.4 mg dm in a 20-cm layer. This corres- ponds to the reserves ofsecondary Zn in the poorest peat soils. Low pH of most peat soils further con- tributes to the high availability and effective utiliza- tion of soil Zn. The above calculation supports the recent finding by Erviö et al. (1990) of the de- cline of ZnAc in the cultivated soils of northern Finland. Soil characteristics strongly affect the response of plant Zn concentration to Zn fertilization. In strongly acid soils Zn application elevates Zn con- centration of grass, also facilitating the mainten- ance of sufficient supply ofZn to plants in peat soils under intensive grassland cultivation. But even high rates of Zn to slightly acid and neutral soils elevate the Zn content of the crop less effectively even if the soils were poor in ZnAc- In those soils, foliar sprays increase plant Zn concentration more effectively. In order to avoid applications of Zn to soil with no fertilizer effect, both soil pH and ZnAc need to be taken into consideration when Zn fertil- izer recommendations are given. Owing to the in- consistent effect of Zn-containing NPK fertilizers on Zn concentration ofcrop, the use of separate Zn fertilizers shouldbe preferred. The reserves of secondary Zn (10 -20 kg ha" 1 in a 20-cm deep plough layer) were of the same mag- nitude as Zn fertilizer recommendations (5 - 20 kg Zn ha’ 1 , Viljavuuspalvelu 1992). The utilization of added Zn is commonly far below 5% and there- fore the recommended application substantially in- creases the reserves of secondary Zn in soil. The low utilization is caused by the strong adsorption of Zn in the soil and not by the reluctance of the plants to take up Zn. This conclusion can be drawn on the basis of the results of pot experiments where high Zn concentration in the grass occurred when Zn was added to an unhumified Sphagnum peat and to strongly acid coarse mineral soils of obviously low Zn adsorption capacities. The large variations of dry matter yield of timo- thy and barley in the field and ryegrass in the pot experiment were not reflected as a negative correla- tion between the size of the yield and the Zn con- centration. This suggests that Zn uptake by the plants is probably not limitedby the capacity factor 262 Agric. Sd. Fint. 2(1993) (quantity ofplant-available Zn in soil) but rather by intensity (Zn concentration in soil solution). The adsorbed Zn fraction is much larger than the dis- solved one, resulting in a strong buffering ofsoil Zn concentration (Elgawhary et al. 1970). As Zn is taken up by plant roots from the soil solution, the decrease of concentration is readily replenished from the adsorbed fraction, provided the soil is not poor in Zn. It can therefore be concluded thatplant uptake does not markedly reduce the Zn concentra- tion of soil solution. Consequently, the Zn concen- tration of plant tissue grown in a given soil can be the same regardless of the size of the yield. The average Zn concentration of cereal crops grown in Finland is at the same level as in other countries of temperate climates. In Norway, in Prince Edward Island, Canada and in southwestern Sweden, mean Zn concentrations ofbarley and oats have ranged between 28 and 48 mg Zn kg’ 1 (FROSLIE et al. 1983, Winter and Gupta 1987, Eriksson et al. 1990). Also timothy grown in Fin- land has on average at least the same Zn concentra- tion as has been reported elsewhere (METSON et al. 1979,Winter and Gupta 1983,BoiLAetal. 1985). Owing to the great variation in Zn concentrations of timothy and barley (Jaakkola and Vogt 1978, Kähäri and Nissinen 1978), it is likely that in areas of poor soil Zn, locally produced fodder may contain much less Zn than is the national average. The level of dietary Zn (50 mg kg' 1 ) recom- mended for cattle in the Nordic countries (NJF 1975, Salo et al. 1990) appears to be high as compared to recommendations given elsewhere. In the USA, a concentration of 40 mg kg' 1 is recom- mended for dairy cattle (NRC 1978) and 20 - 30 mg kg' 1 for beef cattle (NRC 1976). In New Zealand, a recommendation of 15 - 25 mg kg' 1 for grazing livestock is given (Towers and Grace 1983). In a compilation prepared in England (ARC 1980) 30 mg kg' 1 was regarded as the sufficient level in experimental conditions, but it was also pointed out that in studies made in the field higher concentra- tions have occasionally been of advantage. The average Zn concentration of timothy and barley occurring inFinland would thus be considered suf- ficient for cattle in most countries, and the evidence of a general need of a higher Zn level in fodder is not conclusive. Zinc concentration of timothy and barley at least in mineral soils does not reach the level recommended in Finland (50 mg kg' 1 ) with- out excessive Zn fertilization. Because high Zn rates result in an undue accumulation of Zn in the soil, it seems needless to aim at Zn concentrations beyond the current average level in the crop by increased Zn fertilization. The recommended Zn level in the diet should still be reached by direct supplementation into the fodder. Besides soil Zn status, pH and Zn fertilization, also other factors affect the actual Zn concentration in fodder of domestic animals. Clover and other dicotyledons have a higher Zn concentration than gramineous fodder crops (Reay and Marsh 1976, Yläranta and Sillanpää 1984, McLaren et al. 1991). Nitrogen fertilization has also been shown to elevate plant Zn concentration, probably owing to the decrease ofpH (Boawn et al. 1960,Terman et al. 1966). For example, in field experiments by Rinne at al. (1974) and Sillanpää and Rinne (1975) Zn concentration in the grass increased from 30 mg kg' 1 to 39 mg kg' 1 when the N fertilization was increased from nil to 600 kg ha' 1 . On the other hand, the experiments of ETTALA and KOSSILA (1979, 1980) showed that on average 34% ofZn in silage grass was lost during the ensiling. These examples propose that the choice ofcrop as well as different agricultural practices other than Zn fertil- ization can affect the Zn content of the fodder at least as much as was commonly observed to be the effect of Zn application in the current field experi- ments with timothy. Also excessive Zn concentration in plants need to be considered. The highest concentration in rye- grass grown without addedZn, occurring in the soil of Harjavalta, exceeded 100 mg kg' 1 and was of the same magnitude as was reported in grass grown in a Zn-contaminated harbor dredge in the Nether- lands (Smilde et al. 1982). High concentrations of Zn can thus occur locally in the neighborhood of industry also in Finland. The high concentrationof the grass grown in the soil of Harjavalta also shows that Zn accumulated in the soil probably as a result of atmospheric deposition was plant-available. This conclusion is corroborated by findings showing that the bulk of Zn in the deposition both in urban 263 Agric. Sei. Fin!. 2 (1993) (Gatz and Chu 1984) and rural (Lindberg and Harriss 1981) environments is water-soluble. Various plants may exhibit symptoms of Zn tox- icity when the Zn concentration of the plant ex- ceeds 120 - 220 mg kg" 1 (Beckett and Davis 1977, Sauerbeck 1982) but according to the present study, as much as 500 - 700 mg Zn kg" 1 was tolerated by ryegrass with only slight adverse effects. This result agrees with those by Gerza- beck and Schaffer (1989) according to whom the toxicity limit in ryegrass was higher than 400 mg kg" 1 . Tolerance to large doses of Zn by domestic animals appears to be even greater (Miller et al. 1965, Ott et al. 1966). According to Ott et al. (1966), toxicity symptoms occurred only when the dietary Zn concentration exceeded 900 mg kg" 1. The highest Zn fertilization rate currently re- commended in Finland is 20 kg ha" 1 (Vilja- vuuspalvelu 1992), corresponding to 10mg dm"' in a 20-cm thick plough layer. The present pot experi- ments and field experiments by Urvas (1992) showed that at least in strongly acid coarse mineral soils and peat soils Zn concentration of grass can be elevated beyond the recommended level (50 mg kg" 1 ) by application of maximum recommended Zn doses. However, in unpolluted cultivated soils Zn concentration of grass fertilized at that Zn rate is likely to remain below 100 mg kg" 1 . It seems thus evident that aZn concentration toxic to plants or animals cannot be reached when field crops are fertilized with the recommended rates of Zn. REFERENCES Aasen, I. 1981. Mikronaeringsstoff i planter i relasjon til gödsling och forkvalitet. Agric. Univ. Norway B 9/81: 1-13. Al-Hiyaly, S. A. K., McNeilly, T., Bradshaw, A. D. 1990. The effect of zinc contamination from electricity pylons. Contrasting patterns of evolution in five grass species. New Phytol. 114: 183-190. Allen, S. E. & Terman, G. L. 1967. Response of maize and sudangrass to zinc in granular macronutrients. 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Erilaisten Zn-lannoitteiden vaikutusta raiheinän, ti - motein ja ohran satoon ja Zn-pitoisuuteen tutkittiin astia- ja kenttäkokein. Sinkin kokonaispitoisuus (Zn») 106 pinta- maanäytteen aineistossa oli 10 - 202 mg kg' 1 . Kivennäismais- sa Zntot oli positiivisessa korrelaatiossa savespitoisuuden kanssa (r = 0,81 )ja eloperäisissä maissa Zntot korreloi negatiivisesti maan orgaanisen hiilen pitoisuuden kanssa (r = -0,53**). Useiden savimaiden Zntot oli yli 150 mg kg' 1, kun taas muutamien runsaimmin orgaanista hiiltä sisältävien tur- vemaiden Zntoi-varat olivat jopa alle 10 mg kg' 1. Vesiliukoista ja vaihtuvaa sinkkiä (Zttex) uutettiin 0,5 M MgCh-liuoksella Znox korreloi negatiivisesti maan pH:n kanssa. Pääosin orgaa- nisen aineksen sitomaksi oletettua sinkkiä uutettiin 0,1 M ICtPzCH-liuoksella (Znpy ) ja sen jälkeen samasta näytteestä 0,05 M oksalaattiliuoksella (pH 2,9) (Zn ox) Fe- jaAl-oksidien sitomaksi arveltua sinkiä. Summan Znpy + Zriox katsottiin kuvastavan maan sekundaaristen Zn-varojen suuruuttavasta- kohtana rapautumattomien mineraalien sisältämälle sinkille. Sekundaarisen sinkin määrä (mediaani 5,9 mg dm 3, n = 106) oli kaikissa maalajeissa samaa suuruusluokkaa. Sen sijaan sekundaarisen sinkin osuus (%) Zniot :sta oli pienin savimaissa (mediaani 5 %) ja suurin turvemaissa (mediaani 49 %), mikä kuvastaa maan Zntotin määrissä olevia eroja. Maan sinkkiä uutettiin myös viljavuusanalyysissä käytettävällä happamalla ammoniumasetaatti - EDTA -liuoksella (0,5 M CH3COOH, 0,5 M CH3C00NH4,0,02 M Na2-EDTA, pH 4,65). Menetel- mällä saadut tulokset (ZnAc, mediaani 2,9 mg dm'3, vaihtelu- väli 0,6 - 29,9 mg dm'3, n = 106) olivat kiinteässä vuorosuh- teessa Znpy:n kanssa. Voidaankin arvella ZnAC:n sisältävän vesiliukoista, vaihtuvaa, orgaanisen aineksen jaFe- ja Al-ok- sidien sitomaa sinkkiä. ZnAc:n pitoisuus olimuokkauskerrok- sessa lähes poikkeuksettasuurempi kuin jankossa. Astiakokeessa, jossa kasvatettiin neljä satoa raiheinää, ei maan Zn-varoja saatu ehdytetyiksi, vaikka raiheinän sinkin- saanti vähenikin muutamista turvemaista kokeen loppua kohti. Kasvit ottivat 2 - 68 % (mediaani 26 %, n = 107) sekundaarisen sinkin (Znpy + ZnD x) varoista. Suhteellisesti runsaimmin Zn-varat ehtyivät happamista, niukasti sinkkiä sisältävistä turvemaista ja muutamista karkeimmista kiven- näismaista. Suhteellisesti vähiten Zn-varat ehtyivät runsaasti ZnAc sisältävistä maista sekä niukemmin ZnAc sisältävistä neutraaleista maista. ZnAc kuvasti melko hyvin raiheinän Zn- ottoa, joskin menetelmä näyttää hieman yliarvioivan kasvin sinkinsaantia maista, joissa oli kesimääräistä korkeampi pH. Kivennäismaissa pH sääteli selvimmin sitä, kuinka tehok- kaasti sinkkisulfaattina maahan lisätty Zn (10 mg dm 3) ko- hotti raiheinän Zn-pitoisuutta. Maan pH:n kohotessa Zn-lan- noituksen teho heikkeni. ZnAC:n niukkuus maassa lisäsi Zn- lannoituksen tehoa. Zn-lannoitus kohotti raiheinän Zn-pitoi- suutta eniten niissä eloperäisissä maissa, joiden Zn-varoilla oli taipumus ehtyä suhteellisesti voimakkaimmin. Sinkkilannoituksen vaikutusta timotein Zn-pitoisuuteen tutkittiin kahdessa kaksivuotisessa kenttäkokeessa savi- ja hietamaalla. Ilman Zn-lannoitusta kasvaneen timoitein keski- määräinen Zn-pitoisuus oli savimaalla 28 mg kg 1 ja hieta- maalla 35 mg kg' 1 . Sinkkisulfaattina tai rakeisen kipsin ja sinkkisulfaatin seoksena kokeen alussa annettu 3 ja 6 kg Zn ha' 1 lannoitus nosti timotein sinkkipitoisuutta 3ja7 mg kg' 1 . Kun näitä lannoitteita levitettiin nurmen pintaan ensimmäisen sadonkorjuuvuoden keväällä, oli vaikutus sama kuin nurmen kylvön yhteydessä maahan muokatulla lannoituksella. Nur- men pintaan levitettyjen sinkkiä sisältävien NPK-lannoittei- den Zn-lannoitusvaikutus oli vähäinen. Kolmivuotisissa kent- täkokeissa ilman Zn-lannoitusta viljellyn ohran jyvien Zn-pi- toisuus oli savimaalla 29 mg kg' 1 , hietamaalla 18 mg kg' 1 ja multamaalla 39 mg kg' 1 . Zn-lannoitus (5,4 kg ha 1 kerralla kokeen alussa tai yhteensä 4,8 - 5,4 kg ha' 1 kolmessa osassa) kohotti jyvän Zn-pitoisuutta savimaalla (pH 5,8) 5 mg kg 1, muna sillä ei ollut vaikutusta hietamaalla (pH 7,1) eikä multamaalla (pH 5,3), jonka jankko sisälsi runsaasti sinkkiä (ZnAc 17,2 mg dm'3 ). Lehti lannoitteena annettu NajZn-EDTA (1,8 kg Zn ha' 1 vuosittain) kohotti jyvän Zn-pitoisuutta kaikis- sa kokeissa 3-4 mg kg 1 . Hietamaahan sinkkisulfaattina annettu runsaampi lannoitus (15 ja 30 kg Zn ha' 1) kohotti jyvän Zn-pitoisuutta 5 tai 7 mg kg' 1, mutta vaikutusta ei havaittu enää seuraavana vuonna, mikä osoittaa sinkin heik- koa käyttökelpoisuutta kyseisellä neutraalilla maalla. Sinkki- lannoitus ei vaikuttanut timotein tai ohran sadon määrään. Maan pH vaikuttaa ratkaisevasti sekä luontaisen että var- sinkin lannoitteena annetun sinkin käyttökelpoisuuteen. Tästä syystä maan sinkkianalyysin (ZnAc) tulkinnassa ja lannoitus- suosituksia annettaessa olisi otettava huomioon myös maan pH. Neutraaleilla mailla on turha antaa Zn-lannoitusta maa- han sen vähäisen vaikutuksen takia; niillä on mieluummin käytettävä lehtilannoitusta. Happamammissa oloissa myös maahan annettu lannoitus kohottaa kasvien Zn-pitoisuutta. 270 Aghc. Sei. Finl. 2 (1993) Soils used in the methodological studies Number and location Soil class Particle size composition pm, Vo Organic C pH Vo <2 2-20 20-60 201 Kirkkonummi 202 Mäntsälä Heavy clay Silty clay Silty clay Silty clay Sandy clay 65 28 6 6.6 5.4 54 31 5 4.0 5.6 203 Liljendahl 204 Tarvasjoki 205 Tammisaari 206 Lapinjärvi 207 Pälkäne 52 25 6 2.5 5.5 40 41 14 2.5 5.7 39 22 18 5.1 6.8 Very fine sand Very fine sand Very fine sand Very fine sand Silt 28 26 23 2.7 5.4 23 31 31 3.1 5.8 208 Siuntio 209 Helsinki 210 Koski HI 211 Vihti 20 28 17 1.5 5.7 20 20 34 2.7 4.9 17 43 21 3.7 5.2 Fine sand Mull 10 6 8 1.5 4.5 212 Pälkäne 213 Koski Hl 34 41 15 27.0 5.3 Mull 22 48 18 28.0 6.8 Appendix 1 Appendix 2. Characteristics of the soils of surface soil material. Fe„, and Alox stand for oxalate-extractable Fe and Al, respectively. Number and Soil class pH Organic C Particle size composition urn, % Feox Alox Bulk location % 2 . 20 20. 60 >6O mmolkg-' density kg dm ' Clay soils: 1 Somero Heavy clay 6.82.9 74 17 3 6 106 71 0.98 2 Somero Heavy clay 5.37.7 67 24 4 5 134 172 0.76 3 Somero Heavy clay 6.13.0 67 18 5 10 126 75 0.98 4 Kylmäkoski Heavy clay 5.94.7 66 19 9 6 93 141 0.94 5 Somero Heavy clay 6.42.2 66 8 4 22 118 73 1.03 6 Jokioinen Heavy clay 7.02.0 64 10 5 21 80 70 1.04 7 Ypäjä Heavy clay 6.02.3 63 22 6 9 100 55 1.00 8 Kirkkonummi Gyttja clay 5.74.1 58 34 5 3 76 124 0.88 9 Loimaa Clay loam 5.82.9 56 23 7 14 70 69 1.05 10 Kirkkonummi Gyttja clay 4.63.7 56 30 11 3 121 84 0.85 11 Vehkalahti Clay loam 6.01.9 55 24 13 8 87 57 1.10 12 Vihti Gyttja clay 5.49.5 51 41 7 1 79 133 0.76 13 Perniö Silty clay 6.73.2 51 31 11 7 172 66 0.88 14 Loimaa mlk Silty clay 5.92.4 49 44 3 4 92 69 1.03 16 Koski TL Clay loam 5.72.0 45 31 15 9 79 57 1.14 17 Helsinki Clay loam 6.43.5 43 22 21 14 102 57 1.05 18 Valkeala Clay loam 6.22.5 42 37 17 4 55 49 1.12 19 Valkeala Clay loam 6.52.4 42 36 18 4 60 47 1.12 20 Mustasaari Silty clay 5.26.1 40 43 14 3 166 96 0.69 21 Kuhmoinen Clay loam 6.43.2 39 37 12 12 80 74 0.85 22 Vehkalahti Clay loam 6.11.2 39 32 19 10 90 55 1.08 23 Tampere Silty clay 6.22.2 37 54 5 4 83 85 0.90 24 Valkeala Silty clay 5.72.6 35 31 14 20 69 57 1.01 25 Valkeala Silty clay 5.91.4 35 31 15 19 87 51 1.14 26 Ylihärmä Silty clay 5.07.0 32 45 18 5 144 86 0.72 Coarse mineral soils and moraines: 27 Vihti Loam 6.32.0 29 34 22 15 60 56 1.18 28 Korpilahti Silt 6.60.8 27 51 17 5 65 34 1.05 29 Vihti Loam 5.72.0 27 27 11 35 58 52 1.16 30 Laihia Loam 6.23.1 25 37 32 6 91 50 1.00 31 Tarvasjoki Loam 5.22.2 25 32 28 15 90 46 1.13 32 Luumäki Loam 6.42.4 24 45 19 12 59 33 1.00 33 Ylistaro Loam 6.32.3 24 46 16 14 94 49 1.01 34 Pyhäselkä Loam 5.02.7 23 41 23 13 88 57 0.94 35 Isokyrö Silt 6.82.1 23 52 21 4 128 36 1.00 36 Ylivieska Loam 5.82.7 22 44 27 7 80 37 0.97 37 Huittinen Loam 6.22.0 22 36 23 19 77 43 1.01 38 Hollola Silt 6.44.8 21 64 12 3 87 96 0.77 39 Luumäki Silt 6.13.1 20 50 19 11 57 26 0.95 40 Tervola Loam 4.25.3 16 45 27 12 210 29 0.84 41 Alavieska Sandy moraine 6.04.0 16 24 10 50 103 48 1.04 42 Maalahti Very fine sand 5.03.1 16 27 48 9 56 56 0.96 43 Vihti Loam 6.21.9 15 39 33 13 51 41 1.08 44 Lammi Loam 6.02.7 12 42 37 9 59 137 0.87 45 Alavieska Sandy moraine 6.23.0 11 21 28 40 115 39 1.07 46 Lapinlahti Sandy moraine 6.11.9 11 17 10 62 50 40 1.18 47 Sonkajärvi Fine sand 5.62.9 9 18 21 52 62 57 1.08 48 Kitee Very fine sand 5.92.5 9 35 41 15 63 133 1.03 49 Maaninka Fine sand 5.81.8 8 19 29 44 66 49 1.09 50 Sotkamo Silt 6.31.3 8 59 17 16 72 55 0.99 51 Vihti Sandy moraine 6.42.4 8 9 7 76 45 70 1.21 52 Ylivieska Sandy moraine 5.23.1 7 13 23 57 31 45 1.10 53 Siikajoki Sandy moraine 6.32.6 7 9 16 68 85 32 1.31 54 Saari Sandy moraine 6.43.3 6 15 30 49 231 28 1.14 Appendix 2. Number and Soil class pH Organic C Particle size composition urn, % Feox Alox Bulk location % <2 2 . 20 20.60 >6O mm°' kg" t de "sity ,kg dm-' 55 Liperi Sandy moraine 6.03.0 6 14 27 53 29 81 1.11 56 Joroinen Fine sand 6.31.7 6 15 16 63 39 64 1.16 57 Jyväskylä mlk Very fine sand 5.61.5 6 29 51 14 61 122 1.10 58 Lapua Fine sand 6.14.2 5 10 25 60 22 51 1.00 59 Ristiina Sandy moraine 5.83.2 5 12 17 66 47 109 1.16 60 Ristiina Sandy moraine 6.12.0 5 13 9 73 41 104 1.26 61 Hammarland Sandy moraine 6.90.7 5 3 3 89 17 9 1.43 62 Kauhava Sandy moraine 6.73.4 4 8 43 45 19 43 1.06 63 Liminka Sandy moraine 5.82.7 4 8 46 42 55 25 1.15 64 Vihti Fine sand 6.51.9 4 4 6 86 46 104 1.30 65 Jalasjärvi Fine sand 6.32.0 4 7 24 65 25 35 1.10 66 Muhos Fine sand 5.46.1 3 6 5 86 10 74 0.89 67 Närpiö Fine sand 5.25.1 3 4 38 55 33 57 0.96 68 Pieksämäki Sandy moraine 5.92.6 3 11 28 58 19 32 1.10 69 Ruovesi Fine sand 7.41.5 3 4 16 77 48 122 1.26 70 Ähtäri Sandy moraine 5.82.2 3 7 10 80 42 178 1.22 71 Harjavalta Fine sand 7.12.1 3 8 21 68 11 16 1.10 72 Hammarland Fine sand 4.92.0 2 3 4 91 17 23 1.24 73 Kuusamo Sandy moraine 5.42.7 2 8 16 74 95 10 1.14 74 Sotkamo Sandy moraine 5.32.3 1 4 5 90 18 51 1.26 Organogenic soils: 75 Sotkamo Mull 6.212.4 2 11 43 44 88 40 0.77 76 Sotkamo Mull 5.112.8 5 24 15 56 94 95 0.71 77 Maaninka Mull 5.514.4 22 44 14 20 120 117 0.55 78 Savitaipale Mull 5.714.8 10 17 29 44 70 86 0.69 15 Vihti Mull 5.018.3 27 56 14 3 93 225 0.64 79 Vihti Mull 5.119.0 75 20 3 2 54 266 0.76 80 Muhos Mull 5.820.3 4 11 10 75 249 17 0.70 81 Sievi Mull 4.821.3 14 57 24 5 131 85 0.54 82 Ylivieska Mull 5.021.4 25 55 16 4 147 127 0.57 83 Sotkamo Mull 5.621.5 42 48 10 0 108 120 0.61 84 Eno Mull 5.821.9 8 20 17 55 235 42 0.58 85 Honkajoki Mull 5.722.0 9 42 28 21 65 53 0.59 86 Savitaipale Mull 5.822.5 16 25 28 31 87 72 0.60 87 Forssa Mull 5.522.6 68 19 7 6 145 151 0.72 88 Tammela Carex peat 5.623.9 n.d. n.d. n.d. n.d. 102 74 0.55 89 Sotkamo Carex peat 5.024.3 n.d. n.d. n.d. n.d. 135 67 0.46 90 Närpiö Carex peat 4.725.1 n.d. n.d. n.d. n.d. 252 26 0.54 91 Jokioinen Carex peat 6.228.7 n.d. n.d. n.d. n.d. 122 97 0.52 92 Joroinen Carex peat 5.029.9 n.d. n.d. n.d. n.d. 107 222 0.48 93 Sonkajärvi Carex peat 4.530.2 n.d. n.d. n.d. n.d. 100 100 0.29 94 Längelmäki Carex peat 5.232.3 n.d. n.d. n.d. n.d. 82 249 0.44 95 Pyhäselkä Ligno Carex peat 5.534.0 n.d. n.d. n.d. n.d. 232 28 0.44 96 Sotkamo Ligno Carex peat 4.638.0 n.d. n.d. n.d. n.d. 90 94 0.35 97 Sotkamo Carex peat 5.538.8 n.d. n.d. n.d. n.d. 132 154 0.31 98 Pudasjärvi Ligno Carex peat 4.939.8 n.d. n.d. n.d. n.d. 223 76 0.27 99 Yli-Ii Ligno Carex peat 5.540.5 n.d. n.d. n.d. n.d. 202 29 0.26 100 Rantsila Ligno Carex peat 3.840.5 n.d. n.d. n.d. n.d. 147 83 0.36 101 Vaala Ligno Carex peat 6.045.0 n.d. n.d. n.d. n.d. 165 48 0.31 102 Kuusamo Sphagnum 5.545.0 n.d. n.d. n.d. n.d. 95 10 0.27 Carex peat 103 Valtimo Ligno Carex peat 4.847.3 n.d. n.d. n.d. n.d. 70 94 0.30 104 Säkylä Carex peat 4.748.0 n.d. n.d. n.d. n.d. 29 64 0.27 105 Suomussalmi Ligno Carex peat 4.149.2 n.d. n.d. n.d. n.d. 44 53 0.25 106 Muhos Ligno Carex peat 5.149.8 n.d. n.d. n.d. n.d. 196 52 0.34 107 Mikkeli Carex peat 4.450.4 n.d. n.d. n.d. n.d. 62 205 0.39 n.d. = Not determined Some physical and chemical characteristics of soil profile samples. Profile 1: Tarvasjoki, loam (0-38 cm), clay loam (38-120 cm) Depth Clay Org. C pH cm % "tn 0-30 25 1.85.5 32-38 29 0.46.2 38-46 34 0.26.4 50-60 41 0.26.8 65-80 51 0.26.8 85-100 56 0.47.0 105-120 55 0.67.0 Profile 3: Vihti, silty clay (0-60 cm), heavy clay (60-120 cm) Depth Clay Org. C pH cm % % 0-30 50 2.66.3 30-40 53 0.56.7 40-60 54 0.46.8 60-80 72 0.57.0 80-100 88 0.57.1 100-120 86 0.67.1 Profile 5: Sotkamo, Carex peat (20-130 cm), mineral soil mixed in the plough layer Depth Clay Org. C pH cm % % 0-20 6 9.35.7 20-30 n.d. 52.25.4 30-40 n.d. 48.55.2 40-60 n.d. 51.85.4 60-80 n.d. 46.85.5 80-100 n.d. 39.65.5 100-120 n.d. 30.65.6 120-130 n.d. 31.55.6 Profile 7: Muhos, Carex peat (0-110 cm), fine sand (110-125 cm) Depth Fine 1' FS2 ) Org. C pH cm % % % 0-30 n.d. n.d. 44.75.3 30-50 n.d. n.d. 55.14.7 50-70 n.d. n.d. 52.14.7 70-90 n.d. n.d. 55.84.9 90-110 n.d. n.d. 54.25.0 110-125 3 56 0.25.0 n.d. = Not determined " <0.06 mm " Fine sand (0.06-0.2 mm) Profile 2: Vihti, strongly layered silt Depth Clay Org. C pH cm % % 0-27 17 3.26.0 30-40 11 0.26.8 40-50 12 0.26.6 50-70 17 0.26.6 70-90 6 0.16.6 90-100 16 0.16.7 110-120 27 0.26.9 Profile 4: Sotkamo, strongly podzolized fine sand Depth Fine" FS2> Org. C pH cm % % % 0-30 18 55 5.06.0 30-40 14 63 0.36.0 40-45 3 52 2.85.7 45-60 2 67 0.75.7 60-80 17 75 0.25.6 80-110 11 82 0.15.6 110-120 35 64 0.15.9 Profile 6: Jokioinen, Carex peat (0-40 cm), mud (40-50 cm), heavy clay (50-70 cm) Depth Clay Org. C pH cm % % 0-25 n.d. 30.86.0 30-40 n.d. 30.05.5 40-45 82 16.75.7 50-70 90 1.06.0 70-80 88 0.86.0 Appendix 3. Characteristics of soil sample pairs consisting of plough layer (Ap ) and subsoil (B) samples Location and Horizon Soil class Particle size composition urn, % Org. C pH Zn Ac number " ~~~~ ZTTT' "'» mg dm- 1 <2 2-20 20-60 Somero l 1 Ap Heavy clay 74 17 3 2.96.8 6.1 B Heavy clay 73 12 5 0.66.8 3.3 Somero 2' Ap Heavy clay 67 24 4 7.75.3 3.3 B Heavy clay 66 22 2 1.15.5 0.9 Jokioinen 6 1 Ap Heavy clay 64 10 5 2.07.0 2.8 B Heavy clay 91 5 2 0.66.5 2.1 Somero 3' Ap Heavy clay 67 18 5 3.06.1 5.6 B Heavy clay 75 14 5 0.57.0 2.0 Loimaa mlk 14' Ap Silty clay 49 44 3 2.45.9 4.9 B Heavy clay 60 31 4 0.56.5 2.1 Koski TL 16' Ap Silty clay 45 31 15 2.05.7 3.7 B Silty clay 54 27 16 0.36.6 1.5 Kestilä Ap Very fine sand 6 16 52 2.65.3 1.3 B Very fine sand 5 14 54 2.15.2 0.6 Maaninka 49' Ap Fine sand 8 19 29 1.85.8 5.6 B Very fine sand 6 21 40 0.46.3 0.3 Muhos Ap Fine sand 2 4 4 5.85.5 1.5 B Fine sand 2 2 3 0.44.9 0.9 Rantsila Ap Loam 12 47 36 7.36.4 1.3 B Carex peat n.d. n.d. n.d. 35.64.8 1.1 Forssa 87' Ap Mull 68 19 7 22.65.7 3.2 B Heavy clay 74 14 8 2.56.0 4.0 Sotkamo 75 1 Ap Mull 2 11 43 12.46.2 2.0 B Carex peat n.d. n.d. n.d. 50.55.8 0.5 Maaninka 77' Ap Mull 22 44 14 14.45.5 2.4 B Carex peat n.d. n.d. n.d. 43.85.4 0.5 Sonkajärvi 93' Ap Carex peat n.d. n.d. n.d. 30.24.5 3.3 B Carex peat n.d. n.d. n.d. 48.04.6 0.4 Kestilä Ap Carex peat n.d. n.d. n.d. 42.35.2 4.1 B Carex peat n.d. n.d. n.d. 48.54.7 0.8 1 Refers to the number of the Ap horizon sample in the surface soil material (Appendix 2) n.d. = Not determined Characteristics of the surface soils: total Zn (Zn lol), and Zn extracted with MgCL (Zn„), pyrophosphate (Zn p) ), oxalate (Znox) and acetic acid-ammonium acetate -EDTA (ZnAc). Znpy and Zn ox were extracted sequentially. Number and location Zn u„ Zn ex Znp> Znos Zn Ac _• mg kg i mg dm ' Clay soils: 1 Somero 186 1.12.8 3.53.8 2 Somero 168 3.38.1 2.93.3 3 Somero 171 1.02.4 2.31.7 4 Kylmäkoski 122 1.03.4 2.22.3 5 Somero 189 1.14.5 4.44.4 6 Jokioinen 187 0.52.0 4.42.8 7 Ypäjä 150 1.24.1 3.73.7 8 Kirkkonummi 157 1.35.2 3.43.0 9 Loimaa 146 2.34.8 3.13.7 10 Kirkkonummi 108 2.65.4 1.92.8 11 Vehkalahti 148 10 1.82.8 2.1 12 Vihti 66.4 1 5 2.61.2 1.5 13 Perniö 82.8 05 1.42.0 1.1 14 Loimaa mlk 147 2 4 5.43.9 4.9 16 Koski TL 147 2 6 6.14.2 3.7 17 Helsinki 190 49 23.113.0 18.0 18 Valkeala 104 0 7 1.82.1 2.0 19 Valkeala 115 10 3.63.1 4.4 20 Mustasaari 102 3 7 7.83.1 3.4 21 Kuhmoinen 202 06 3.85.2 2.3 22 Vehkalahti 134 11 2.22.7 3.3 23 Tampere 146 07 2.13.1 1.6 24 Valkeala 140 3 7 8.64.8 6.3 25 Valkeala 137 13 2.62.7 3.4 26 Ylihärmä 82.22.7 7.02.3 2.9 Coarse mineral soils and moraines: 27 Vihti 128 0.71.6 1.91.0 28 Korpilahti 92.00.5 2.61.7 0.8 29 Vihti 117 1.01.8 1.91.3 30 Laihia 109 1.36.6 3.64.1 31 Tarvasjoki 79.82.2 3.62.4 2.3 32 Luumäki 81.60.8 1.81.8 1.9 33 Ylistaro 114 1.26.7 4.65.7 34 Pyhäselkä 106 2.64.3 2.42.5 35 Isokyrö 115 0.75.5 5.05.2 36 Ylivieska 82.11.6 4.02.3 3.8 37 Huittinen 104 0.91.5 2.21.9 38 Hollola 201 0.64.2 4.41.4 39 Luumäki 62.51.3 4.32.2 4.7 40 Tervola 63.83.5 4.11.9 2.9 41 Alavieska 55.90.8 1.91.4 1.5 42 Maalahti 66.82.2 4.21.4 2.7 43 Vihti 92.60.6 2.62.6 1.9 44 Lammi 112 0.71.4 1.80.8 45 Alavieska 45.70.6 2.01.4 1.5 46 Lapinlahti 68.92.1 5.12.5 3.3 47 Sonkajärvi 57.12.2 3.81.5 2.4 48 Kitee 74.60.6 2.21.4 1.4 49 Maaninka 102 1.02.7 2.41.7 50 Sotkamo 58.00.5 2.11.7 2.1 51 Vihti 57.90.4 1.41.4 1.7 52 Ylivieska 26.51.3 2.20.8 1.8 3 Number and location Zn 101 Zn„ Znpy Znox Zn Ac mg kg- 1 mg dm- 1 53 Siikajoki 78.15.3 23.98.8 29.9 54 Saari 70.30.5 3.32.5 1.9 55 Liperi 45.01.2 4.31.4 2.7 56 Joroinen 76.70.8 4.83.4 2.5 57 Jyväskylä mlk 68.61.4 3.61.8 2.8 58 Lapua 35.20.8 4.00.9 2.3 59 Ristiina 62.92.4 7.73.6 5.4 60 Ristiina 64.80.8 4.92.7 3.4 61 Hammarland 37.40.4 1.41.2 1.5 62 Kauhava 37.70.6 3.20.9 2.1 63 Liminka 45.11.6 2.21.1 1.6 64 Vihti 40.60.4 2.11.7 1.5 65 Jalasjärvi 29.20.5 1.80.6 0.9 66 Muhos 14.01.1 2.00.5 1.3 67 Närpiö 43.33.1 5.60.9 4.2 68 Pieksämäki 27.00.9 2.60.8 2.0 69 Ruovesi 69.40.3 2.03.7 2.9 70 Ähtäri 52.85.6 13.64.0 12.7 71 Harjavalta 420 22.0 227 115 165 72 Hammarland 29.93.8 4.90.6 4.5 73 Kuusamo 15.12.6 3.51.4 3.8 74 Sotkamo 30.58.3 12.72.4 11.0 Organogenic soils: 75 Sotkamo 40.30.9 2.61.2 2.0 76 Sotkamo 31.82.4 5.11.1 2.4 77 Maaninka 63.82.5 5.11.2 2.4 78 Savitaipale 33.11.3 5.81.4 2.9 15 Vihti 67.53.3 8.92.3 5.2 79 Vihti 59.41.7 5.62.6 3.9 80 Muhos 20.01.5 3.31.0 2.2 81 Sievi 42.77.7 15.22.0 6.4 82 Ylivieska 49.82.1 4.71.7 2.1 83 Sotkamo 45.11.3 1.61.1 0.8 84 Eno 36.42.3 9.02.6 4.3 85 Honkajoki 75.87.0 26.93.5 14.0 86 Savitaipale 39.22.0 7.71.6 3.7 87 Forssa 80.11.8 7.92.4 3.2 88 Tammela 41.74.2 13.81.9 5.6 89 Sotkamo 70.87.6 9.32.0 4.9 90 Närpiö 42.25.1 12.21.5 5.4 91 Jokioinen 63.41.7 8.12.3 3.0 92 Joroinen 48.64.8 12.42.4 5.4 93 Sonkajärvi 44.33.8 7.71.5 2.9 94 Längelmäki 32.2 2A 4.43.1 1.7 95 Pyhäselkä 85.610.8 53.810.3 19.4 96 Sotkamo 27.18.4 13.41.5 3.7 97 Sotkamo 10.31.1 2.20.7 1.8 98 Pudasjärvi 18.13.3 6.31.6 1.5 99 Yli-Ii 24.13.5 14.62.2 3.5 100 Rantsila 34.311.0 16.91.7 5.0 101 Vaala 41.45.8 28.33.3 8.0 102 Kuusamo 32.86.0 26.12.7 6.8 103 Valtimo 11.51.9 2.60.5 0.6 104 Säkylä 22.05.6 15.81.6 4.0 105 Suomussalmi 12.34.6 7.31.1 1.6 106 Muhos 15.44.3 9.51.6 2.5 107 Mikkeli 25.38.9 17.51.7 5.5 Some characteristics of the soils of two pot experiments (Sections 4.3 and 5.2.1) and the field experiments. Ap = plough layer, B = subsoil (30-35 cm). Soil and crop Organic C Particle size composition urn, % pH Zn Ac % me dm - ' <2 2-20 20-60 >6O 8 Pot experiments Clay loam 2.3 48 25 18 9 6.2' 0.9 Fine sand 1.0 7 3 46 44 5.9' 2.8 Carex peat 27.2 n.d. n.d. n.d. n.d. 6.2 1 4.8 Sphagnum peat 41.7 n.d. n.d. n.d. n.d. 3.6 1 3.7 Field experiments with timothy Clay loam A„ 3.4 42 30 13 15 5.71.6 B 0.8 58 23 8 11 5.91.5 Fine sand A„ 1.4 9 4 6 81 5.93.3 B 0.7 4 1 12 83 6.10.7 Field experiments with barley Clay loam Ap 2.9 33 28 19 20 5.82.1 B 0.6 35 26 22 17 6.11.0 Fine sand A„ 1.3 5 3 6 86 7.11.3 B 0.8 4 1 5 90 6.3 0.2 Mull A„ 22.9 38 45 11 6 5.34.7 B 32.0 n.d. n.d. n.d. n.d. 5.0 17.2 1 pH of the unlimed soils of the pot experiments n.d. = Not determined Field experiment; Effect of Zn fertilizers on timothy in the field Sowing: 1990 Experimental years: 1991 and 1992; two crops in each year Method: Randomized blocks Plot size: 2.3 m x 10 m Harvested area: 1.6 x 10 m Replicates: 4 Soils: Clay and fine sand Crop: Timothy, cultivar ’Tammisto’ (15 kg ha 1) Application of Zn: A total of 3or6kg ha 1 during the experiment (5.2 kg ha 1 in NPK 18-3-12; Control: no Zn applied) Application of N, P and K: at sowing 57, 34 and 37 kg ha 1 , respectively (NPK 14-9-10 400 kg ha 1); in spring and after the first harvest in each year 90-93, 31-33 and 61-65 kg ha 1, respectively Herbicide in fine sand in spring 1991: bentazone - MCPA (Basagran MCPA) Application of Zn and NPK fertilizers in the field experiments with timothy: Treatmen Zn NPK kg ha* 1 fertilizer 1 1. Control; no Zn application 2. ZnS0 4 • 7H 20 mixed into the soil in fall 1990 3. ’Sinkkilannos’ » » 4. ’Sinkkilannos’ onto the sward in spring 1991 5. Coated NPK II » » 6. ZnS0 4 ■ 7H,0 mixed into the soil in fall 1990 7. ’Sinkkilannos’ » » 8. ’Sinkkilannos’ onto the sward in spring 1991 9. NPK 18-3-12 onto the sward in spring and summer 10. Coated NPK 111 » » 0 3 3 3 4x0.75 6 6 6 4x 1.3 4x1.5 I I 1 1 3 1 1 I » 2 4 1 1 = NPK 17-6-12 530 kg ha 1 2 = NPK 18-3-12 500 kg ha* 1 , Triple superphosphate90 kg ha-1 3 = Coated NPK II 360 kg ha* 1, NPK 17-6-12 170 kg ha* 1 4 = Coated NPK 111 360 kg ha ', NPK 17-6-12 170 kg ha 1 Dates of farming operations: Clay: Fine sand: Sowing Aug. 27, 1990 Aug. 17, 1990 Spring fertilization May 16, 1991 May 9, 1991 Harvest 1/91 June 26, 1991 June 26, 1991 Summer fertilization June 28, 1991 June 28, 1991 Harvest 11/91 Aug. 13, 1991 Aug. 12, 1991 Spring fertilization May 10, 1992 May 12, 1992 Harvest 1/91 June 10, 1992 June 9, 1992 Summer fertilization June 10, 1992 June 9, 1992 Harvest 11/92 Sept. 18, 1992 Sept. 17, 1992 Appendix 7. Field experiment: Different fertilizers as Zn sources for tiarley Experimental years: 1990, 1991 and 1992 Method: Randomized blocks Plot size: 2.3 m x 10 m Harvested area: 1.5 mx 10 m Replicates: 4 Soils: Clay, mull and fine sand Crop: Barley, cultivar ’Kymppi’ (clay and fine sand soil), cultivar ’Kalle’ (mull soil) Application of Zn: A total of 5.4 kg ha 1 during three years (4.8 kg ha-' in NPK 18-3-12; Control: no Zn applied) Application of N. P and K: 108-110, 19-20 and 74-76 kg ha 1 , respectively, to clay and fine sand soil, 110, 39 and 73-78 kg ha 1 , respectively, to mull soil Herbicides: mixtures of mecoprope, dichlorprope and MCPA (Dipro, Hormoprop, Hormoneste); tribenurone-methyle (Express) Fungicide: propiconazole (Tilt) Insecticide (in 1992 only); dimethoate (Roxion), supermetrine (Ripcord) Growth regulators: chlormequate chloride (CCC), mepiquate chloride, etephone (Terpal) Application of Zn and NPK fertilizers in the 3-year field experiments with barley: Treatment Zn NPK kg ha ' fertilizer 1 1. Control; no Zn application 0 ] 2. ZnS04 • 7H 20 24 kg ha-' in the first spring 5.4 1 3. 'Sinkkilannos' 180 kg ha' 1 in the first spring 5.4 1 4. Na 2 Zn-EDTA 12 kg ha-' sprayed onto the soil annually 3x 1.8 1 5. NPK 18-3-12, 610 kg ha 1 annually 3x 1.6 2 6. Coated NPK I annually 3x 1.8 3 7. Na 2 Zn-EDTA 12 kg ha-1 sprayed annually onto the foliage 3x 1.8 1 1 In clay and fine sand soil: 1 = NPK 25-4-4 440 kg ha 1, KCI 110 kg ha-' 2 = NPK 18-3-12 610 kg ha* 1 3 = Coated NPK I 460 kg ha->, KCI 110 kg ha 1 In mull soil: 1 = NPK 17-6-12 650 kg ha 1 2 = NPK 18-2-12 610 kg ha* 1 . Triple superphosphate 105 kg ha* 1 3 = Coated NPK 1 460 kg ha* 1, Triple superphosphate 105 kg ha* 1 , KCI 110 kg ha 1 Dates of farming operations and length of the growing period: Clay Mull Fine sand 1990: Sowing April 30 June 6 Aug. 16 109 d May 7 June 6 Aug. 20 105 d May 4 June 6 Aug. 16 104 d Foliar application of Na2Zn-EDTA Harvest Growing period 1991: Sowing May 13 June 28 Aug. 28 107 d May 27 July 03 Sept. 2 98 d May 15 June 28 Aug. 27 104 d Foliar application of Na2 Zn-EDTA Harvest Growing period 1992: Sowing May 21 July 7 Aug. 17 88 d May 27 June 30 Aug. 31 96 d May 21 July 1 Aug, 26 97 d Foliar application of Na2 Zn-EDTA Harvest Growing period Appendix 8. Field experiment: Zinc concentration of barley as affected by different Zn rales Experimental years: 1991 and 1992 Method: Randomized blocks Plot size: 2.3 m x 5 m Harvested area: 0.5 m 2 (two subsamples of 0.25 m 2) four times during the growing period Replicates: 4 Soils: Clay and fine sand Crop: Barley, cultivar ’Kymppi’ (270 kg ha* 1) Application of Zn: 15 or 30 kg Zn ha* 1 as ZnS04 • 7Hz O in spring of 1991, (Control: no Zn applied) Application of N, P and K: 110, 22 and 44 kg ha* 1, respectively (Fertilizer: NPK 20-4-8 550 kg ha* 1) Herbicide: tribenurone-methyle (Express) Insecticide (in 1992 only): dimethoate (Roxion) Growth regulator: chlormequate chloride (CCC) Dates of sowing, sampling and harvesting and length of the growing period: 1991 1992 Clay Fine sand Clay Fine sand Sowing Sampling at Feekes 2 Sampling at Feekes 5 Sampling at Feekes 10.5 Harvest Growing period May 17 June 24 July 8 July 26 May 16 June 24 July 5 July 24 Aug. 28 104 d May 21 June 18 July 3 July 21 Aug. 20 91 d May 20 June 15 June 29 June 20 Aug. 24 96 d Appendix 9.