I Maataloustieteellinen A ikakauskirja Vol. 61: 55—59, 1989 Effect of cumulative fertilizer dressings on the phosphorus status of mineral soils I Changes in inorganic phosphorus fractions HELINÄ HARTIKAINEN Department of Agricultural Chemistry, University of Helsinki, SF-00710 Helsinki, Finland Abstract. Surface soil samples were collected from 16 P fertilization trials before onset of the experiments and after seven years of cultivation. The changes in the inorganic P frac- tions were investigated in plots amended annually with 0, 30 or 60 kg of P ha~'. In the clay soils, cultivation without P fertilization depleted the NH4F-extractable and NaOH-extractable P reserves by 22—69 kg ha-1 ; in the coarser soils, the respective depletion was B—l4o8 —140 kg ha-1 . H 2 S04 -soluble P decreased in seven soils by 16—34 kg ha -1 . In the plots amended to- tally with 210 or 420 kg of P ha-1 , on the other hand, these P fractions increased by 24—174 and 46—368 kg ha-1 , respectively. The higher the P dressing was, the more the added P tended to accumulate in the fluoride-soluble form as compared to the alkali-soluble form. Index words: P accumulation, residual P, inorganic P fractions Introduction Effective P sorption by A 1 and Fe com- pounds is typical of Finnish mineral soils (Kaila 1963, 1964, 1965, Hartikainen 1979). Efficient retention restricts losses by leaching, but also diminishes the availability of P to plants. Laturi (1977) calculated that the an- nual uptake of added P by yields averages 30 %, but much lower estimations have been published recently (Saarela and Sippola 1987). Thus, during recent decades, a succes- sive build-up of residual P has taken place in Finnish cultivated soils amended with large quantities of fertilizer P. The long-term effect of fertilization inten- sity on different inorganic P reserves has been studied only sparsely under field condi- tions in which management practices, partic- ularly ploughing, cause dilution of residual P in the uppermost layers. Store dressing with rock phosphate has been found to result in a quite permanent P enrichment in acid-soluble form (see Hänninen and Kaila 1960, Kaila 1969), whereas superphosphate has been demonstrated to accumulate in NH 4F-soluble and NaOH-soluble fractions (Kaila 1961). There are, however, no data available on the 55 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND changes that occur in various P fractions in plots cultivated for several years without P fertilization. The present study reports the P accumulation found in a seven-year field ex- periment with increasing superphosphate treatments and the depletion in P reserves in plots that received no P fertilizers. Material and methods The soil samples were collected from 16 P fertilization trials carried out by the Institute of Agricultural Chemistry and Physics, Agricultural Research Centre, at several re- search stations in Finland. The trials involved five treatments where the P quantity added an- nually varied from 0 to 60 kg ha~'. The ex- perimental crops were mainly cereals, but pea and grasses were also cultivated. The fields were composed of four blocks, each of which contained all the treatments. Five of the fields represented clay soils (>3O % clay fraction <2 pm), 11 being coarser mineral soils. Characteristics of the soils are given in Table 1. The particle-size composition of mineral material was deter- mined according to the pipette method of Table I. Characteristics of soils at the beginning of the field trials. Locality Clay pH Org.C % % mmol/kg Clay soils 1 Mietoinen 74 5.73.1 73 53 2 Mietoinen 35 4.92.9 85 34 3 Mietoinen 59 5.33.3 80 47 4 Mouhijärvi 33 5.63.8 62 64 5 Mouhijärvi 35 4.83.5 61 47 Coarser soils 6 Kokemäki 25 5.0 10.0 97 94 7 Pälkäne 12 4.8 3.2 46 59 8 Maaninka 8 5.4 2.3 68 45 9 Laukaa 26 5.5 3.5 60 30 10 Toholampi 6 4.6 4.2 68 98 11 Toholampi 18 4.2 11.1 138 102 12 Mikkeli 3 4.8 6.2 25 152 13 Mietoinen 24 4.8 2.3 52 31 14 Tohmajärvi 5 4.9 4.5 56 133 15 Ylistaro 27 4.6 8.9 85 133 16 Anjala 25 5.4 12.6 45 93 Elonen (1971), and the organic C content was measured by a modified Alten wet com- bustion method (Graham 1948). Aluminium (Al 0) and iron (Feo ) were extracted with an acid (pH 3.3) 0.05 M NH 4 -oxalate solution at a soil to solution ratio of 1:20. Before the start of the trial, a volume of soil was gathered from each experimental field, air-dried and used as a control sample. The other samples were taken at the end of the trial from plots fertilized for seven years with 0, 30 or 60 kg of P ha~' annually. Each of the air-dried and 2 mm sieved subsamples was analyzed separately for pH in a 1:2.5 (w/v) 0.01 M CaCl2 suspension and for inorganic P fractions by a modified Chang and Jackson procedure (Hartikainen 1979). The P con- centration in the extracts was determined by the molybdenum blue-stannous chloride meth- od of Kaila (1955). Results and discussion The inorganic P fractions in soils at the be- ginning of the trials and the changes that oc- curred during the seven-year period as a result of different fertilization backgrounds are shown in Table 2. The results, given in kg ha~‘ per plough layer of o—2o0—20 cm, were cal- culated by assuming the bulk density of soil to be 1 kg dm~3. These are only rough esti- mates, because the sampling sites in the fields after the trials cannot exactly coincide with those before the experiments. Furthermore, owing to the great variation between the repli- cates, the changes in the P fractions, though great, were not always statistically significant. In the following, the uncertain changes were not included in the calculations. Al-P and Fe-P in Table 2 refer to the NH4F-soluble and NaOH-soluble fractions assumed to represent P mainly bound by hydrated A 1 and Fe oxides, respectively. Sev- en years of cultivation without P addition depleted these reserves by 2—15 °7o in the clay soils and by 2—17 % in the coarser soils. In absolute quantities, the reduction in the clay soils ranged from 22 to 69 kg ha~', in the 56 57 Table 2. P fractions in experimental soils (kg ha-1 ) and the changes in them during seven years of cul- tivation. Changes in plots that received totally P kg ha -1Soil P frac- Con- lion trol 0 210 420 I Al-P 93 —23** 0 43** —8 37** 79***Fe-P 388 Ca-P 668 2 Al-P 198 —2l* —lB* 5 —22* 10 42*** —l7 29 87*** 15 —4O —lO —ls** 42*** 108*** —22* 67** 117*** —2l* 30*** 57*** 23* 33** 97*** Fe-P 688 Ca-P 763 3 Al-P 115 Fe-P 462 Ca-P 760 4 Al-P 297 Fc-P 600 —23 21 69** —3 17 0Ca-P 557 5 Al-P 110 Fc-P 342 —27** 10 42*** —42*** —4 33* —27* —4 13 —4 24» 98** —62» —lO —l6 Ca-P 297 6 Al-P 372 Fe-P 670 Ca-P 596 10 —2O —l2 7 Al-P 118 —B* 38** 76*** 12 8 20»Fc-P 254 Ca-P 320 8 Al-P 274 —32 —24* —l4 —so**» 40** 150*** —s6** 2 22 —24 —6 60 Fe-P 544 Ca-P 2240 9 Al-P 264 0 56»* 100»** Fe-P 424 Ca-P 946 22 14 44* 28* 34*** 26** —3B* 30* 116***10 Al-P 210 Fe-P 246 —32* 8 54*** 16* 0 4Ca-P 220 11 Al-P 256 Fc-P 858 16 60* 154»** —s4* 114*** 214*** —34* —l6 —3O —B6* 58* 46* Ca-P 324 12 Al-P 656 Fe-P 112 Ca-P 194 16 12 —2 —22* 0 20* —2o* 0 74***13 Al-P 110 Fe-P 380 Ca-P 728 —42** 4 20 10 —l2 12 —7B*** —l4 46***14 Al-P 364 Fe-P 404 Ca-P 302 46*» —6 6 —2B* —6 —l2* —96*** 0 —lO _44* 24* 72** —36 —l6 —l4 —7o** 34* 112»** —B* 10 52** 15 Al-P 310 Fc-P 522 Ca-P 594 16 Al-P 390 Fe-P 198 Ca-P 352 —6 0 —8 * = differs from the control at P =0.05 ** = » » » at P =0.01 **» = » » » at p = n nnat P = 0.001 coarser soils from 8 to 140 kg ha~', the aver- age being 35 and 74 kg ha-1 , respectively. The H 2S0 4-soluble fraction, denoted as Ca-P in Table 2, decreased significantly in seven soils, the depletion being 16—34 kg ha-1 . The slight increase in these reserves found in soil 9 may be attributable to inaccuracies in sampling. It is noteworthy that in soil 8, the acid- soluble fraction was 2—lo fold higher than in the other soils, and remained unaffected by the fertilization regimens. Heavy dressings with rock phosphate may result in marked in- creases in H 2S0 4-P (cf. Kaila 1969), but ac- cording to the information available at the Maaninka research station, no store dressing has been performed during past decades (K. Rinne oral communication, 19 Öct., 1988). On the other hand, the experimental field is located near the region where apatite is mined. Therefore it is likely that the high acid-soluble fraction was derived from native apatite reserves of the soil material. In acid Finnish soils, the H 2 S0 4-soluble fraction is consid- ered to represent mainly primary apatitic P (Kaila 1964), even though in soils treated with P fertilizers the acid extractant may also dissolve secondary Ca phosphates (Kaila 1961). In studies where P is added e.g. as a K compound, this fraction has, however, been found to be quite inactive (Kaila 1964, Har- tikainen 1979). The P fertilization increased the NH4F- soluble and NaOH-soluble reserves in all but four soils, for which no significant changes in these fractions were observed. The recovery of fertilizer P amounted to 11 —83 % and 11 —88 % of the total P additions of 210 and 420 kg ha respectively. The accumulation in the A 1 and Fe bound forms was highest in the very acid soil 11 (pH in CaCl 2 4.2) rich in oxalate-soluble Fe. In the untreated control samples, the ratio of NH 4F-P to NaOH-P correlated moderately with the ratio of Al c to Fe H , the value of r being o.7s*** (n=ls). When soil 12, which was very high in Al 0 , was included, the r value rose to o.96***. Nevertheless, the paired t-statistics revealed that in the soils amended with the lower P quantity, the NH 4F-P/NaOH-P ratio was significantly higher than in the control sam- ples, but lower than in the soils treated with heavy P dressings. This finding indicates that the higher the P dressing was, the more inten- sively the added P tended to accumulate in the fluoride-soluble fraction. The acid-soluble P seemed to increase only in soils 3, 9 and 12. This does not mean, how- ever, that no accumulation of fertilizer P as Ca compounds took place in other soils. Kai- la (1961) demonstrated that in soils recently dressed with superphosphate, dicalcium phos- phate, a reaction product of monocalcium phosphate, may be attacked by the NH4F ex- tractant in the earlier phase of the fractiona- tion procedure. References Elonen, P, 1971. Particle-size analysis of soil. Acta Agr, Fenn. 122; 1—122. Graham, E. 1948. Determination of soil organic matter by means of a photoelectric colorimeter. Soil Sci. 65: 181 183. Hartikainen, H. 1979. Phosphorus and its reactions in terrestrial soils and lake sediments. J. Scient. Agric. Soc. Finl. 51: 537—624. Hänninen, P, & Kaila, A. 1960. Field trials on the store dressing with rock phosphate. J. Scient. Agric. Soc. Finl. 32: 107—117. Jaakkola, A., Syvälahti, J. & Saari, E. 1982. Contents of mineral elements in Finnish cereal straw. J, Scient. Agric. Soc. Finl. 54: 385 —394. Kaila, A. 1955. Studies on the colorimetric determina- tion of phosphorus in soil extracts. Acta Agr. Fenn, 83: 25—47. Kaila, A. 1961. Fertilizer phosphorus in some Finnish soils, J. Scient. Agric. Soc. Finl. 33: 131—139. In the plots amended annually with 60 kg of P per ha-1 , the P addition markedly ex- ceeded the P withdrawal by yields, estimated on the basis of nutrient uptake data of Jaak- kola et ai. (1982). In many soils the recovery of residual P, however, remained quite small. This may be attributable to the uneven distri- bution of added P in soils, owing to the place- ment of fertilizers in bands. The uneven dis- tribution, in turn, was reflected in the large variation between replicates, which decreased the statistical significance of the observed changes. Acknowledgement. The author wishes to thank Prof. Paavo Elonen and Dr. Into Saarela, Agricultural Research Centre, and the staff of the research stations for their help in collecting the soil samples. Financial support by the Academy of Finland is gratefully acknowledged. Kaila, A. 1963. Fertilizer phosphorus in various frac- tions of soil phosphorus. J. Scient. Agric. Soc. Finl. 35: 36—46. Kaila, A. 1964. Fractions of inorganic phosphorus in Finnish mineral soils. J. Scient. Agric. Soc. Finl. 36: 1 13. Kaila, A. 1965. The fate of water-soluble phosphate ap- plied to some mineral soils. J. Scient. Agric. Soc. Finl. 37: 104—115. Kaila, A. 1969. Residual effect of rock phosphate and superphosphate. J. Scient. Agric. Soc. Finl, 41: 82—88. Laturi, R. 1977. Typpi-, fosfori- ja kaliumlannoituksen kehitys Suomessa. Kehittyvä Maatalous 36: 3—lo. Saarela, 1. & Sippola, J. 1987. Kalkituksen vaikutus kasvien fosforin saantiin. Koetoiminta ja Käytäntö 44: 52. Ms received July 25, 88 58 SELOSTUS Pitkäaikaisen su peri osfaat tilannoil uksen vaikutus kivennäismaiden fosforitilaan I Epäorgaanisen fosforin fraktiomuutokset Helinä Hartikainen Helsingin yliopisto, Maanviljelyskernian laitos, 00710 Helsinki Tutkimuksessa selvitettiin muokkauskerroksen epäor- gaanisissa fosforivaroissa tapahtuneita muutoksia pitkä- aikaisessa kenttäkokeessa. Maanäytteet oli koottu Maa- talouden Tutkimuskeskuksen eri tutkimusasemilla olleista 16 fosforilannoituskokeesta ruuduilta, joita oli viljelty seit- semän vuotta ilman fosforilannoitusta tai joille oli vuo- sittain annettu 30 tai 60 kg P:a ha~' superfosfaattina. Verlailunäytteet oli otettu koekentiltä ennen kokeiden pe- rustamista. Rinnakkaisnäytteiden suuren hajonnan vuoksi käsit- telyjen väliset erot eivät aina olleet tilastollisesti merkit- seviä. Voitiin kuitenkin arvioida, että raudan ja alumi- niumin sitomaksi oletetut fosforireservit vähenivät lan- noittamattomissa savimaissa 22 —69 jakarkeammissa ki- vennäismaissa B—l4o8 —140 kg ha-1 . Kalsiumin sitomat varat pienenivät seitsemässä maassa 16—34 kg. Lannoitetuis- sa koeruuduissa oli yleensä havaittavissa fosforin kerty- mistä raudan ja aluminiumin sitomaan fraktioon: pienem- män lannoitemäärän (yhteensä 210 kg) aiheuttama ker- tymä hehtaaria kohti oli savimaissa 33—109 ja suurem- man (yhteensä 420 kg) 75 —225 kg. Vastaavat muutok- set karkeampien kivennäismaiden fosforivaroissa olivat 2—174 ja 46—368 kg. Mitä suurempia lannoitemäärät oli- vat, sitä suurempi osa maahan kertyneestä fosforista näyt- ti pidättyneen aluminiumin sitomaan fraktioon. 59