Maataloustieteellinen A ikakauskirja Vol. 56: 291—298, 1984 Peat ash and basic slag as substitutes for lime with reference to phosphorus uptake by turnip rape HELINÄ HARTIKAINEN University of Helsinki, Department of Agricultural Chemistry, 00710 HELSINKI, Finland Abstract. The effect of peat ash and basic slag on the P supply to turnip rape was com- pared with that of calcitic and dolomitic limestone in a pot experiment performed with two acid mineral soils of pH 4.8 (CaCl2 ). Changes in soil properties induced by various liming agents were investigated in an analogous incubation test, and the results served to interpret the observations made in the pot experiment. When the liming materials were added in equal quantities, their ability to reduce soil acidity decreased in the sequence: calcite > dolomite > basic slag > peat ash. However, their growth-promoting effect appeared only in the second year and was not related to the neu- tralizing ability. In the muddy fine sand soil (3.0 % of org. C) poor in water-soluble P, the peat ash and basic slag were equally effective as calcite in increasing the dry matter yields. In the fine sand soil (6.4 % oforg. C), the basic slag and dolomite significantly increased the second yield. The efficiency of peat ash and basic slag seemed to be attributable to their positive impact on P resources. In fact, peat ash served as a slowly acting P-fertilizer rather than as a liming agent. In the basic slag treatment, an increased silicate concentration obviously resulted in desorption of P. In the P-deficient muddy fine sand, the peat ash was equivalent to calcite in intensifying the P uptake. On the otherhand, in the fine sand soil where the polymerization of Al due to an increased pH obviously resulted in enhanced P retention, the P uptake was higher in the soils treated with peat ash and basic slag than in those amended with conven- tional liming agents. Introduction Finnish soils are typically acid and rather poor in available P. Therefore liming and P fertilization are essential measures in agricul- ture. As shown e.g. by Salonen et al. (1973), the utilization of added P by plants is, however, markedly dependent on the P sorption properties of soil. Phosphate reten- tion, in turn, is affected by pH (Obihara and Russell 1972, Parfitt 1977, Barrow 1984 etc.). Therefore, liming can be expected to affect the phosphate-supplying power of soils. In Finland, calcitic and dolomitic limestone is conventionally used as liming agent, but Index words; soil acidity, liming materials, silicate, phosphorus desorption, phosphorus uptake 291 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=9IYQvs1nA6zq4uSV.rdPEEY2w-tsSZyv6y4zmiw.crKgO01t1dw5PK_CUaNdk67xBUvlSukFgOq63JEeLoJcJQybqgu3VRAMWVMH2CAsIMhNHdyUcS7ZtC1wVMqqf75Md1elszTfAF12sDKpYKvL-J1Bi2_UHGlaIQFTq9C4mK7x5cNChDNuuAcHhePkWemgmf2RlcI82jkXhedInMseoOj-uA recently various basic waste materials and in- dustrial byproducts have increasingly become available for this purpose. Yet, the informa- tion on the efficiency of these alternative liming materials, especially in relation to P nutrition of plants, is still insufficient. The purpose of the present pot experiment was to compare the P utilization by turnip rape in two acid mineral soils amended with peat ash or basic slag with that in soils treated with calcitic or dolomitic limestone. The impact of various liming materials on soil properties and P extractability was investigated in more detail in a concurrent incubation experiment. Materials and methods Two acid surface soil samples were taken from the experimental farm of Helsinki Uni- versity. Their characteristics are given in Table 1. For thepot experiment, carried out in 1980 and 1981, Mitscherlich-pots were filled with 4.5 kg of moist soil, corresponding to 3.9 kg of air-dried muddy fine sand and 3.6 kg of air-dried fine sand. The soils were treated with 24 g of calcitic limestone, dolo- mitic limestone, peat ash or basic slag. The liming agents contained various P fractions, analyzed by a slightly modified Chang and Jackson method according to Hartikainen (1979) as follows: P (mg/kg) extracted by NH4 CI NH 4F NaOH H 2 SQ4 Calcite 0.4 0.0 1.5 0.0 Dolomite 0.1 0.0 1.5 0.0 Peat ash 569 906 322 4828 Basic slag 2.1 17.5 0.0 20.8 The other properties have been reported by Jokinen (1982). Half of thepots were amended with 400 mg of P (added as K 2HP04), corresponding to 104 mg and 114 mg per kg of the muddy fine sand and fine sand, respectively. The pots not treated with P received an equivalent quantity of K as KCI. The amounts of other Table 1. Characteristics of experimental soil samples. Muddy Fine sand fine sand Clay % 22.4 22.5 pH (CaCl2) 4.8 4.8 Org. C % of D. M. 3.0 6.4 P-fractions NH„CI-P ppm 3.4 10.0 NH„F-P » 107 321 NaOH-P » 286 277 H2 S04 -P » 325 285 KCI-extractable AI ppm 44.8 29.7 NH 4OAc- » » » 130.0 176.4 plant nutrients applied to all soils are given in a previous paper (Hartikainen 1983 b). Twenty seeds of turnip rape (Brassica cam- pestris v. oleifera f. annua) were sown in each pot. In an analogous incubation experiment, performed in plastic pots, the quantities of soils, liming agents and plant nutrient salts were 1/10 of those used in the pot experi- ment. Both experiments were carried out with four replicates. Plant analyses. After harvesting, the plant material was first dried at 60° C and there- after heated at 105°C for two hours, ground- ed and digested with the acid mixture of HCI04 : H 2S0 4 : HN0 3 (1 : 2,5 : 10) (Schar- rer and Munk 1956). The filtered extracts were analyzed for P by an ammonium vana- date method (Jackson 1958). Soil analyses. In the incubation experi- ment, air-dried subsamples were analyzed af- ter 4 and 16 months of incubation, in the pot experiment after 2 years of cultivation. Soil pH was measured in 0.01 M CaCl2 solution. Water-soluble P was extracted by a slightly modified van der Paauw (1971) and Sissingh (1971) method. Inorganic P was fractionated according to a modified Changand Jackson method (Hartikainen 1979). The exchange- able A 1 was displaced with four portions of 1 M KCI in theratio of soil to solution of 1; 5 (w/v) and determined by an Aluminon meth- od of Yuan and Fiskell (1959). 292 Results a) Incubation experiment The base strength of the liming agents, rated by comparing their effects on the soil pH, varied markedly and decreased in both Table 2. pH and exchangeable Al in soil samples in- cubated for 4 months with or without various liming agents.* Liming pH (CaCl2 ) Al mg/kg treatment _ p added _ p added Muddy fine sand 99.2* 88.8f 7.3» 6.7» 6.9» 6.9» Unlimed 4.3» 4.4» Calcite 6.4* 6.5 b Dolomite 6.0 f 5.9f Peat ash 4.6b 4.7' Basic slag 5.1 d 5.2' 61.3' 50.1“ 18.2' 14. l b Fine sand 63.9 f 54.4' 6.9» 7.5» 5.9» 6.7» Unlimed 4.5» 4.5» Calcite 5.9' 5.9= Dolomite 5.6d 5.6d Peat ash 4.7b 4.7b Basic slag 5.1' 5.1' 40.4d 34.1' 14.3b 12.6b * Both soils are tested separately. The means followed by a common letter do not differ at P = 0.05. Table 3. Water-soluble P in the soils incubated with various liming agents without P addition and the recovery of added P in water-soluble frac- tion.* HjO-soluble P mg/kg Recovery %Liming agent Incubation time, months 4 16 4 16 Muddy fine sand Unlimed 5.4» 5.7»1 * 8.0 5.5 Calcite 7.3' 6.1»b'd 8.2 6.3 Dolomite 6.8 d' 6.6cd' 7.7 6.4 Peat ash 5.8» 1* ö.S 1*11 ' 7.4 5.3 Basic slag 5.5“ 5.6ab 8.3 6.6 Fine sand Unlimed 28.9* 29.5' 15.0 12.2 Calcite 23.6b 20.7» 11.9 8.7 Dolomite 24.9“ 23.8b ' 10.8 8.1 Peat ash 29.1' 26.5d 10.1 10.6 Basic slag 25.6'“ 24.9b 'd 12.7 10.3 Both soils are tested separately. experimental soils in the following sequence: calcite > dolomite > basic slag > peat ash (Table 2). The peat ash treatment did not totally counterbalance a decrease in soil pH due to incubation and nutrient salt addi- tion (from 4.8 to 4.3—4.5). A prolonged in- cubation did not significantly affect the soil acidity. That is why the pH values at the end of the experiment only are presented. All the liming materials were more effective in the muddy fine sand soil. Its lower pH buffering power appeared also in that the pH in soils amended with K 2HP04 tended to be a little higher than in those without P addition. Table 2 further reveals that the ef- ficiency of various liming agents to reduce the exchangeable A 1 was related to their ability to decrease soil acidity. As expected, in the calcite- and dolomite-treated soils with final pH of 5.9—6.5, this A 1 fraction had practi- cally disappeared. In the other treatments, the P addition resulted in a further depression in exchangeability of Al. In the experimental soils a reduction in acidity affected the solubility of P in an opposite direction. Table 3 shows that the 4-month incubation tended to increase the water-soluble P in the muddy fine sand and to decrease that in the fine sand soil. The data reveal also a tendency of P intensity being the more affected the more a given liming agent raised the pH. A long-term in- cubation reduced the solubility of P into water in the calcite-treated samples and in the fine sand samples supplied with peat ash. Further, the sorption of added P was lower by the fine sand richer in native water-soluble P than by the muddy fine sand soil (Table 3). After a 4-month incubation, water extracted 7.4—8.3 % of the P added to the muddy fine sand soil and 10.1—15.0 % of P added to the fine sand soil. The recovery data indicate the impact of liming to have been quite similar on fertilizer P and the soil P resources. The prolonged treatment reduced the recovery in all soils. According to the results of the fractiona- tion analyses (data not presented) the various 293 liming treatments tended to decrease the NaOH-soluble P (by 9—23 mg/kg) and to in- crease the NH 4F-soluble P (by 4—28 mg/ kg), to some extent also the H2S04-extract- able fraction (by o—l20— 12 mg/kg), in the soils incubated without P addition. It its notewor- thy, however, that in the soils supplied with peat ash also the NaOH-P was markedly in- creased (by 26—30 mg/kg). In fact, the P applied with peat ash was recovered mainly in the NH 4F- and NaOH-soluble fractions. b) Pot experiment Table 4 shows that the liming agents af- fected the dry matter yields only in the second year. In the muddy fine sand the shoot yields increased, except in the dolomite-treated soils. In the fine sand soil, on the other hand, only dolomite and basic slag significantly improved plant growth. In this soil, also the positive effect of P addition appeared just in the second harvest, in the unlimed or calcite- treated soils. Inversely, the P fertilization was necessary for the muddy fine sand. In the first year it did not affect plant growth in soil supplied with basic slag, but its positive residual effect was marked also in this treat- ment. In general, the P content was higher in the shoots harvested from the fine sand soil than in those harvested from the muddy fine sand: without P fertilization the range in the first yield was 3.50—4.68 %o and 3.82 4.30 %o, in the second one 2.24—3.46 %o and 2.46—2.69 %o, respectively. Table 5 re- veals that the P removal from the muddy fine sand soil without P addition was not af- fected by the liming agents in the first year, but was markedly promoted by the peat ash and calcite treatments in the second year. The residual effect of ash was noticeable even in soils fertilized with P. In terms of total uptake the dolomite seemed to be the least effective. In the fine sand soil, on the contrary, the liming treatments did not significantly en- hance the P withdrawal despite increased dry matter yields. There was rather a tendency of the calcite and dolomite additions impeding the P nutrition also in the soils supplied with fertilizer P. Only the P treatment was capable of promoting the P uptake, but to a lesser ex- tent than in the muddy fine sand. Further, a comparison between the various liming ma- terials demonstrates the superiority of the peat ash and basic slag. Although the withdrawal of soil P was intensified in the muddy fine sand soil by various liming materials, the residual water- Table 4. Dry matter yields (g/kg of soil).* Liming Year 1980 Year 1981 Total treatment p app |j ecj p appiied P applied Muddy fine sand Unlimed 5.3“ 9.2'“' 1.3“ 4.4“ 6.6“ 13.6“ Calcite 6.5“»' 10.9' 3.8'“ 6.4' 10.3b 17.38“ Dolomite 5.6ab 9.6“' 2.3“ b 4.5“ 7.9“b 14.1' Peat ash 5.6“ b 9.5“' 3.9'“ 6.6' 9.5 ab 16.1'“ Basic slag 7.l ab'“ 8.3b'“' 2.9 bc 6.5' 10.0b 14.8'“ Fine sand Unlimed 8.4“ b 10. l“ b 5.7“ 7.8»' 14.1“ 17.9b'“ Calcite 8.1“ 10.6“b 6.4“ b 8.9' 14.5“b 19.5“ Dolomite 8.8“ b 11.3» 7.4»' 7.5»' 16.2“»'“ 18.8'“ Peat ash 8.2“ 8.8“» 7.1“» 8.1»' 15.3“»' 16.9“»'“ Basic slag 7.9“ 9.4“» 7.6»' 8.9' 15.5“»' 18.3»'“ * Both soils and years are tested separately. 294 soluble P was slightly decreased only in the basic slag treatment (Table 6). In the fine sand soil, on the contrary, the residual water- soluble P decreased by liming, but not by peat ash treatment. In most cases the liming treatments did not affect the extractability of residual P in the soils supplied with K2HP04 . Only the calcite-induced reduction in the fine sand soil was statistically significant. Discussion In the muddy fine sand soil poor in water- soluble P, the first dry matter yields increased by the P additions but were not affected by the liming agents. This suggests the shortage of P to have been a growth-limiting factor. The fine sand soil contained abundantly easi- ly soluble P. Therefore the P fertilization showed some positive effect only in the sec- ond year after the resources were depleted by the withdrawal of the first harvest. The various liming treatments affected the shoot yields and the P uptake only in the second year. In the P-deficient muddy fine sand, a liming-induced increase in P removal seemed to be associated with an increase in dry matter yields, whereas in the fine sand soil there was no unambiguous relationship between the quantities of plant material har- vested and P withdrawal. In fact, the incuba- tion test showed that the experimental soils Table 5. Amounts of P (mg/kg of soil) taken up by yields.* Liming Year 1980 Year 1981 Total treatment _ p applied _ p app | ied _ P applied Muddy fine sand Unlimed 19.4“ 41.7' 3.4“ 16. I d 22.8“ 57.8'“ Calcite 24.3“ 48.1' 9.5»' 16.0“ 33.8b 64.1“* Dolomite 24.1“ 42.3' 5.4“» 12.6'“ 29.5“ b 54.9' Peat ash 23.2“ 43.6' 10.3' 21.6' 33.5b 65.2d Basic slag 29. l*b 7.2“ b 16.9“' 36.3b 54^ Fine sand Unlimed 38.5“ b 50.0 b' 20.1“ b 33.l f 58.6“ b 83.1' Calcite 33.0“ 45.5“»' 16.7“ 27.4'd' 49.7“ 72.9»' Dolomite 33.2“ 56.4' 16.6“ 23.4»'“ 49.8“ 79.8' Peat ash 33.6“ 45.7“»' 23.1»' 32.3'f 56.7“ 78.0' Basic slag 35.3“» 47.7“»' 24.1»'d 28.5“'r 59.4“» 76.2' • Both soils and years are tested separately. Table 6. Effects of various liming treatments on residual water-soluble P (mg/kg) in cultivated soils. Muddy fine sand Fine sand Liming agent P applied P applied Calcite —0.08“ +0.07“ —6.B4*** —4.80* Dolomite —0.36“ +0.99“ —5.25** —4.20“ Peat ash —0.16“ +0.73“ +0.33“ +2.40“ Basic slag —0.98* —1.04“ —2.46* +1.35“ ns. = not significant • = P < 0.05 ** = P < 0.01 *** = P < 0.001 295 represented soil types of dissimilar responses to liming treatment in regard to P extract- ability: in the muddy fine sand soil the water- soluble P tended to increase and in the fine sand soil to decrease withrising pH, irrespec- tive of the liming material used. This observa- tion was made also in a previous incuba- tion study where the same soil samples were treated with increasing quantities of calcite (Hartikainen 1983 a). The results of the pot experiment reveal, however, that the efficiency of different liming agents in improving plant growth or P withdrawal was not related to their capacity to reduce the soil acidity. In both soils, pH was raised most by calcite, followed by dolo- mite, basic slag and peat ash. Nevertheless, in the muddy fine sand soil cultivated with- out P addition calcite and peat ash increased most effectively the shoot yields and the basic slag was superior to dolomite. Except for dolomite, the liming agents significantly en- hanced also the total P uptake. However, despite increased P removal, the residual water-soluble P was slightly decreased only in the basic slag treatment, which allows to con- clude that these agents increased the available P in soil. In the fine sand soil, the efficiency se- quence of the liming materials was dissimi- lar: dolomite and basic slag significantly increased the dry matter yields in soils not treated with P, but the effect of calcite and peat ash remained insignificant. However, only basic slag and peat ash tended to pro- mote the P uptake, whereas the conventional liming agents seemed to depress it, even in soils fertilized with K2HP04. Also the re- sidual water-soluble P in the calcite- and dolomite-treated soils was decreased, which gives a further indication of a reduction in P availability. These results suggest that, in addition to the neutralizing ability, also other properties of the liming agents were conducive. Peat ash rich in P obviously served as a slowly acting P fertilizer rather than as a liming agent. It is noteworthy that the P contained in the ash was mainly of an acid-soluble form, but after a 4-month incubation in soil the bulk of it was recovered in NH 4F- and NaOH-extractable fractions. This indicates the solubility of P to have increased during the incubation. Thus, it seems likely that it took longer than one year for the peat ash to benefit the P-deficient muddy fine sand. Inversely, the basic slag was very poor in P, but contained abundantly Si which was shown in several studies (reviewed e.g. by Fidanovski (1968)) to intensify plant growth. There are numerous interpretations of the mechanism of action of Si. In the present study, however, its beneficial effect seemed to be attributable to an increased availability of soil P due to the silicate addition, as re- ported by Semb (1943), Ganssmann (1961), etc. Silicate is specifically sorbed by soil col- loids (Hingston et al. 1967) and its addi- tion is known to result in the desorption of previously sorbed phosphate (Obihara and Russell 1972, Smyth and Sanchez 1980). In contrast to some earlier studies (e.g. Scheffer et al. 1982), the phosphate mobili- zation by silicate seemed to occur despite a relatively low soil pH. Recently, also Haynes (1984) has stated the pH(KCI) values to be lower in soils amended with CaSi03 than in soils treated with a chemically equivalent quantity of Ca(OH)2, but the effect of form of liming material on estimates of phosphate availability depended upon the soil extractant used. Accordingly, the extraction test of Scheffer and Scheffer (1984) demonstrated the silicate addition to increase calcium lactate-soluble P less than did lime, but the pot experiment showed the silicic acid effect of Hiittenkalk to be of longer duration than that of CaO. It should be pointed out, however, that in the present study no liming-induced in- crease in the P uptake amounted to that brought about by a rather high P addition. Nevertheless, in the unlimed muddy fine sand, an increase in shoot yield due to the P fertilization did not significantly differ from that caused in the first year by calcite and 296 basic slag treatment, and in the second year by calcite and peat ash treatment. Further, the comparison of present results with those obtained by Jokinen (1982) with the same soils without Mg addition supports the con- clusion that the growth-promoting effect of basic slag and peat ash would be attributable to their impact on P resources rather than to their role as Mg or Ca sources. The efficiency sequence of the liming ma- terials was dissimilar in the experimental soils, indicating the usefulness of a given agent to be controlled also by soil properties. In the fine sand soil, the inefficiency of peat ash and basic slag to elevate soil pH was a factor actually promoting the availability of P. A previous study (Hartikainen 1983 a) implied the detrimental effect of liming in this soil to be attributable to the abundance of polymerized A 1 the affinity of which for P retention increased with increasing pH. It can be supposed that much higher quantities of limestone are needed to overrule the po- lymerization of A 1 and to start the desorp- tion of P. The results demonstrate that base quantities adequate to neutralize the ex- changeable A 1 cannot be used as a reliable measure of lime requirement, especially in soils rich in organic matter. The P mobility estimates obtained in the incubation experiment by simple water ex- traction seemed to underestimate the ef- ficiency of the alternative liming agents in promoting the P uptake. Obviously, this was partly due to a high nutrient salt application enhancing the P adsorption. Further, the pH data of limed soils suggest that, as far as the P nutrition of plants is concerned, the usefulness of various materials cannot be evaluated only on the basis of their neu- tralizing ability. References Barrow, N.J. 1984. Modelling the effects of pH on phosphate sorption by soils. J. Soil Sci. 35: 283—297. Fidanovski, F. 1968. Silicium, ein fiir die Pflanzen niitzliches Element. Z. Pflanzenernähr. Bodenkd. 120: 191—207. Ganssmann, W. 1961. Über die Siliziumbestimmung in Pflanzen und die Aufnahme von Phosphorsaure und anderen Nährstoffen bei Siliziumdiingung. 130 p. Giessen. Hartikainen, H. 1979. Phosphorus and its reactions in terrestrial soils and lake sediments. J. Scient. Agr. Soc. Finl. 51: 537—623. Hartikainen, H. 1983 a. Effect of liming on phospho- rus in two soils of different organic matter content. I Changes of native and applied phosphorus in in- cubation experiment. J. Scient. Agr. Soc. Finl. 55: 345—354. Hartikainen, H. 1983 b. Effect of liming on phospho- rus in two soils of different organic matter content. II Changes in the availability of phosphorus to turnip rape (Brassica campestris). J. Scient. Agr. Soc. Finl. 55: 355—362. Haynes, R.J. 1984. Effect of lime, silicate, and phos- phate applications on the concentrations of extractable aluminium and phosphate in a Spodosol. Soil Sci. 138: B—l 4. Hincston, F.J., Atkinson, R.J., Posner, A.M. & Quirk, J.P. 1967. Specific adsorption of anions. Nature 215: 1459—1461. Jackson, M.L. 1958. Soil chemical analyses. 498 p. London. Jokinen, R. 1982. The efficiency of dolomitic limestone, basic slag and peat ash as liming agents, and as calcium and magnesium sources for turnip rape. J. Scient. Agr. Soc. Finl. 54: 371—383. Jones, L.D.H. & Handreck, K.H. 1967. Silica in soils, plants and animals. Advances in Agronomy 19: 107 149. Obihara, C.H. & Russell, E.W. 1972. Specific adsorp- tion of silicate and phosphate by soils. J. Soil Sci. 23: 105—117. Paauw, F. van der. 1971. An effective water extraction method for the determination of plant-available soil phosphorus. Plant and Soil 34: 467—481. Parfitt, R.L. 1977. Phosphate adsorption on an Oxisol. Soil Sei. Soc. Amer. J. 41: 1064—1067. Salonen, M, Koskela, I. & Kahari, J. 1973. The dependenceof the phosphorus uptake of plants on the properties of the soil. Ann. Agr, Fenn. 12: 161 171. Scharrer, K. & Munk, H. 1956. Zur Methodik der nassen Veraschung in der agrikulturchemischen Ana- lyse. Agrochimica 1: 44 —55. 297 Scheffer, B. & Scheffer, K. 1984. Der Einfluss von Kalk und Kieselsäure auf die Phosphatmobilität (CAL) in Böden. Landwirtsch. Forschung 37: I—B. Scheffer, K., Schreiber, A. & Kickuth, R. 1982, Die sorptive Bindung von Diingerphosphaten im Boden und die phosphatmobilisierende Wirkung der Kie- selsäure. 2. Mitteilung: Die mobilisierende Wirkung der Kieselsäure. Arch. Acker- u. Pflanzenbau u. Bo- denkd. 26: 143—152. Semb, G. 1943. Undersokelser over fosforsyrens opp- loselighet og binding i ostnorske jordtyper. Meldinger fra Norges Landbrukshogskole. 1—145. Sissingh, H.A. 1971. Analytical technique of Pw meth- od, used for the assessment of the phosphate status of arable soils in the Netherlands. Plant and Soil 34: 483—486. Smyth, T.J. & Sanchez, P.A. 1980. Effects of lime, silicate, and phosphorus applications to an Oxisol on phosphorus sorption and ion retention. Soil Sci. Soc. Amer. J. 44: 500—505. Yuan, T.L. & Fiskell, J.G.A. 1959. Aluminium deter- mination. Aluminium studies. Soil and plant analysis of aluminium by modification of the Aluminium method. J. Agr. Food Chem. 7: 115—117. Ms received December 5, 1984 SELOSTUS Turpeen tuhka ja masuunikuona kalkitusaineina kevätrypsin fosforin saannin kannalta Helinä Hartikainen Helsingin yliopisto, Maanviljelyskemian laitos, 00710 HELSINKI Kaksi kasvukautta kestäneessä astiakokeessa vertail- tiin kevätrypsin fosforin ottoa kalkitsemattomista sekä turvevoimalan arinatuhkalla, masuunikuonalla, kalsiit- tikalkilla tai dolomiittikalkilla käsitellyistä maista. Kal- kitusaineita lisättiin yhtä suuret määrät. Kaikki koejäse- net saivat muuten samanlaisen peruslannoituksen, mut- ta puolet astioista jätettiin ilman fosforilisäystä. Kalki- tuskäsittelyjen vaikutuksia maanäytteiden fosforitilaan sekä muihin kemiallisiin ominaisuuksiin selvitettiin koe- järjestelyltään astiakoetta vastanneen muhituskokeen avulla. Kokeissa käytettiin kahta hapanta (pHcacij 4.8) hietamaanäytettä. Kalkitusaineiden happamuutta neutraloiva vaikutus pieneni järjestyksessä: kalsiitti > dolomitti > masuuni- kuona > turpeen tuhka. Ne edistivät toisena vuonna ke- vätrypsin kasvua, mutta sadonlisäykset eivät seuranneet happamuuden vähenemistä. Fosforitilaltaan huonossa liejuisessa hienossa hiedassa (3.0 % org. C) turpeen tuh- ka ja masuunikuona nostivat kuiva-ainesatoja yhtä pal- jon kuin kalsiitti. Karkeassa hiedassa (6.4 % org. C) sa- dot nousivat masuunikuonalla ja dolomiitilla käsitellyis- sä maissa. Turpeen tuhkan ja masuunikuonan tehokkuus perus- tui ilmeisesti niiden suotuisaan vaikutukseen maan fos- forivaroihin. Tuhka sisälsi runsaasti happoliukoista fos- foria, jonka liukoisuus näytti paranevan muhituksen ai- kana. Sen katsottiinkin toimineen pikemminkin hidas- vaikutteisena fosforilannoitteena kuin kalkitusaineena. Masuunikuonan vaikutus perustui ilmeisesti siihen, että silikaatti-ionien konsentraation kasvu edisti fosforin va- pautumista pidätyspaikoilta. Vähän helppoliukoista fosforia sisältäneessä liejuisessa hienossa hiedassa tur- peen tuhka jakalsiitti paransivat fosforin ottoa yhtä te- hokkaasti. Sen sijaan karkeassa hiedassa kalsiitti ja dolomiitti heikensivät fosforin saantia. Ilmeisesti pH:n nousu edisti aluminiumin polymeroitumista ja siten fos- forin pidättymistä. Tuhkalla ja masuunikuonalla käsi- tellyissä koejäsenissä pH:n nousu jäi varsin pieneksi ja fosfori säilyi käyttökelpoisempana. Näyttää siltä, että karkeassa hiedassa olisi kalsiitin ja dolomiitin määrien pitänyt olla suurempia, jotta syntyneiden Al-yhdisteiden pinnoille pidättynyttä fosforia olisi alkanut uudelleen mobilisoitua. 298