JOURNAL OF THE SCIENTIFIC AGRICULTURAL SOCIETY OF FINLAND 126 Maataloustieteellinen Aikakauskirja Vol. 11:126-1)7, 1981 Effect of liming on the magnesium status of some mineral soils and on the fate of fertilizer magnesium RAILI JOKINEN University of Helsinki, Department of Agricultural Chemistry, SF-00710 Helsinki 71, Finland. Abstract: Nine mineral soils were incubated in laboratory without lime (Ca o ) or limed (Ca,) with calcium carbonate (lab.reag.), and without magnesium fertilizer (Mg 0) or fertilized with MgS04 7H 20 (Mg, = 4 mg/100 g soil Mg). The incubation covered a period of seven weeks in aerobic conditions at constant 20 °C temperature. The relative increase in the effective cation exchange capacity (ECEC) caused by liming seemed to be in coarse mineral soils greater than in clay soils. The differences in pH (CaCl 2 ) values between soil types was not so evident. In seven soils of the nine, liming decreased the 0,01 M CaCl2 extractable magnesium content more than in I M KCI or in 1 M neutral ammonium acetate extractable magnesium contents. The limed soils contained ammonium acetate extractable magnesium 2—24 % less than the unlimed soils. The decrease in magnesium content was greatest in acid muddy silt (Littorina soil) and in acid silty clay. Without lime the I M KCI extractable (Al +H) contents of these soils were 6,6 and 2,2 me/100 g soil and pH (CaCl 2 ) 3,9 and 4,5, respectively. In finesand soils liming seemed to increase the magnesium content although not significantly. In limed soils 17—73 %of the fertilizer magnesium was extractable in 0,01 M CaCl 2 , 67—100 % ex- tractable in I M KCI and 57—100 % extractable in 1 M neutral ammonium acetate. The equivalent ratio of exchangeable (1 M ammonium acetate, pH 7) calcium to magnesium in the .oils may give pointers to the choice of liming agents, especially in the liming of low cation exchange capacity soils. Introduction In a pot experiment ryegrass took up magnesium from nine mineral soils less than the exchangeable (1 M neutral ammonium acetate) magnesium content of the soils decreased during the experiment (JOKINEN 1981 a, b). A possible explanation for the decrease in the soil magnesium content might be the fixation by liming of soil magnesium to forms not extractable in ammonium acetate (ADAMS and HENDERSON 1962, CHRISTENSON et al. 1973, KAILA 1974, JUO and UZU 1977). The purpose of this incubation experiment was to elaborate the effects of liming on the magnesium status of the nine mineral soils used as growth base in the pot experiment. The fertilizer magnesium was also the object of research. https://www.c-info.fi/en/info/?token=pY2sM7zi2oePMsCF.Ax7YZ7G47xn2w0ne7h0Czg.EatgDOu_zVcq3IBF6-43jnSOehQ_Q8P7URLwHrZWQLyFyAvf4CUKE1p_83gmbDZ7ajyekNy25zGA-9EfD6ShAKx7NDKUDA39aZT0tVyPeWYNEsJ-iTsKDVm_gZ-r6i8vzezB5de7epCVIQks3gYfjhXcJyAuQlfNL1hA 127 Table 1 Some properties of soils at start of incubation experiment. 1 2 3 4 5 6 7 8 9 Fine- Fine- Very Muddy Silty Sandy Sandy Silty Heavy sand sand fine- silt clay clay clay clay clay sand pH (CaCl 2 ) 4,4 5,1 5,0 3,9 4.5 5,6 5,0 6,1 5,6 Org. C% 1,9 4,7 3,0 6,1 5,7 4,5 5,6 2,8 5,2 Clay % ( 0,002 mm) 4,4 4,5 11,7 25,4 30,9 36,4 43,8 45,1 64,3 Silt %(0,002-0,020 mm) 7,2 15,4 42,3 40,4 5 5,0 41,0 24,5 42,9 13,8 Effective CECmc/100g soil 3,0 7,8 5,7 9,6 9,4 14,8 15,6 19,7 23,9 Exchangeable (I M ammonium acetate, pH 7) Ca 2 + mc/ 100 g soil 1,09 6,86 3,75 2,99 6,61 14,13 11,39 18,58 18,71 Mg 2 + ” 0,11 0,57 1,25 0,55 1,00 1,95 4,30 2,80 6,53 K+ ” 0,24 0,32 0,18 0,38 0,51 1,13 0,59 0,77 1,1 5 0,01 M CaCI 2 extract. Mg mg/100 gsoil 1,10 4,53 12,25 4,53 8,63 14,00 31,75 17,75 40,25 1 M KCI extract. Mg mg/100 gsoil 1,21 5,70 15,06 4,90 1 1,36 21,23 50,06 30,88 73,95 I M KCI extract. (Al +H) me/100 g soil 1,94 0,64 0,78 6.60 2,24 0.32 0,76 0,26 0,36 Materials and methods The incubation experiment was carried out with nine mineral soils. Detailed information of the properties of these soils was presented in the report concerning the magnesium uptake by ryegrass in pot experiment (JOKINEN 1981 b). The pH (CaCl2 ) of the soils varied from 3,9 to 6,1 and the ammonium acetate (1 M, pH 7) extractable magnesium content from 0,11 to 6,53 me/100 g soil (Table 1). The moist soils were air-dryed and crushed in a mortar to pass a 2 mm sieve. For the incubation experiment 200 g soil was weighed in plastic bags (volume 1/2 litre). The soils were treated with calcium carbonate (lab. reag.) and magnesium sulphate (MgS0 4 -7H 20, p.a.), and the amounts of calcium and magnesium per 100 g soil were as follows: Symbols Treatments Ca„Mg( , Without Ca and Mg Ca,,Mg| Without Ca + 4 mg Mg Ca,Mg„ 90, 180 or 360 mg Ca Ca|Mgj 90, 180 or 360 mg Ca + 4 mg Mg The aim of the liming was to raise the pH of the soils to between 6 and 6,5. Because of the differences in the initial pH values of the soils it was necessary to give unequal amounts of lime. The amounts of calcium per 100 g soil were as follows; 90 mg Ca: Fincsand (2), very fmesand, sandy clay (6) and silty clay (8) 180 mg Ca: Fincsand (1), silty clay (5), sandy clay (7) and heavy clay 360 mg Ca: Muddy silt The treatments were replicated four times and the total number of pots amounted to 144. 128 The soils were moistened with de-ionized water to 60 % of the field capacity. The bags were provided with covers full of holes and incubation took place during seven weeks in a room of constant temperature of 20 °C. During this time the moisture of the soils was checked every week and de-ionized water was applied if necessary. After incubation the soils were left to dry to air-dry state, and crushing and sieving were performed as before the incubation. For description of the soil magnesium status three extractants were used: 1) 1 M neutral ammonium acetate is common in determination of the exchangeable mag- nesium, 2) 1 M KCI extracts magnesium in the original pH of the soil, 3) 0,01 M CaCl 2 is used to describe the magnesium activity in soil. The extracting power of NH4 + and K+ should be the same, but the difference is in the buffering ability of the solutions. The soil analysis was performed with the same methods as with the soils of the pot experiment (JOKINEN 1981 b) to determine neutral ammonium acetate extractable calcium, magnesium, potassium and sodium contents, 1 M KCI extractable magnesium, aluminium and hydrogen contents and effective cation exchange capacity, 0,01 M CaCl2 extractable magnesium content and pH. The statistical treatments were performed by means of analysis of variance and the differences between soil treatments by Duncan’s new multiple range test. In the tables the results on the same line provided with the same letter do not deviate significantly (P= 0,05 %). Results After the incubation the pH of almost all soils was near the set target (6,0 6,5); in finesand (2) the pH was somewhat b'-'ow and in silty clay (8) above it. Liming increased significantly the effective cation exchange capacity of the soils (Table 2). In coarse mineral soils and in acid silty clay (5) the relative increase in effective cation exchange capacity seemed to be greater than in clay soils within the uniform calcium supply. The relative increases in ECEC and absolute increases in pH caused by liming (Ca,—Ca o) were as follows; Relative increase Absolute increase Soil in ECEC, % in pH(CaCl2 ) Ca: 90 mg/100 g soil 2. Finesand 41 0,8 3. Very finesand 6. Sandy clay 8. Silty clay 60 1,1 19 0,9 12 0,7 Ca: 180 mg/100 g soil I. Finesand 2,0192 5. Silty clay 7. Sandy clay 9. Heavy clay 75 1,8 42 1,4 33 1,3 Ca: 360 mg/100 g soil 4. Muddy silt 2,2I 18 129 Table 2. The pH(CaCl 2 ), 1 M KCI extractable (Al +H) content and effective cation exchange capacity ECEC (me/100 g soil) of the soils after incubation. CaO MgQ CaO Mg, Ca|Mg(j Ca,Mg| pH(CaCl 2) 1. Fincsand 4,4 a 4,4 a 6,4b 6,7C 2. Fincsand 5,Oa 5,Oa 5,8b 5,9° 3. Very fincsand 5,lb 5,Oa 6,2C 6,2 C 4. Muddy silt 4,0a 4,0a 6,2b 6,2b 5. Silty clay 4,5 a 4,5 a 6,3b 6,2b 6. Sandy clay 5,3 a 5,5 a 6,4b 6,4b 7. Sandy clay 5,Oa 3,lb 6,4 C 6,5d 8. Silty clay 6,2 a 6,2 a 6,9b 7,0C 9. Heavy clay 5,Ja 5,3a 6,6b 6,6b (Al +H) me/100 g soil 1. Fincsand 1,82b 1,8 5 b 0,2l a 0,15 a 2. Fincsand 0,59b 0,59b 0,26a 0,2l a 3. Very fincsand 0,86b 0,82b 0,18 a 0,22a 4. Muddy silt 5,87c 5,94c 0,31 a 0,5 3b 5. Silty clay 1,92b 1,93b 0,20a 0,16a 6. Sandy clay 0,35b 0,36b 0,17 a 0,19a 7. Sandy clay 0,64 d 0,60c 0,2 5 b 0,22 a 8. Silty clay 0,28b 0,26b 0,19a 0,15 a 9. Heavy-clay 0,32 a 0,33a 0,28a 0,2 5 a ECEC me/100 g soil 1. Fincsand 2,9a 3,3 a 8,4b 8,7b 2. Fincsand 7,5 a 8,lb 10,6C 11,2d 3. Very fincsand 5,7 a 6,0b 9,l c 9,3 d 4. Muddy silt 8,9a 9,2 a 19,4b 19,7b 5. Silty clay 8,6 a 9,0 a 15,lb 15,lb 6. Sandy clay 15,5 a 16,0a 18,5b 19,2b 7. Sandy clay 15,4a 13,8a 21,9b 22,4b 8. Silty clay 20,3 a 20,7 a 22,7b 23,lc 9. Heavy clay 24,0a 24,2a 31,8b 32,2b Magnesium fertilization had only slight effect on cither the ECEC or on the pH of the soils. There was no aluminium in sandy clay (6), silty clay (8) and heavy clay extractable in KCI (1M) and therefore the results in Table 2 expressing the (Al+H) contents indicate the amounts of hydrogen in these soils. In muddy silt the aluminium content amounted to 65 % of the (Al+H) content, in other soils either the content of aluminium and hydrogen was equal (silty clay 5) or the aluminium content was less than that of hydrogen. Because of liming the (Al+H) content of all soils decreased significantly except in heavy clay. From limed soils KCI extracted only hydrogen. Magnesium fertilization increased significantly the (AJ+H) content in muddy silt. The KCI (1 M) extractable magnesium content in all untreated incubated soils was 88—98 % of the magnesium extractable in ammonium acetate (1 M, pH 7, Table 3). In muddy silt the KCI extractable magnesium amounted to 78 % respectively. 130 Tabic 3. Magnesium content (mg/100 g) of the soils extractable in I M neutral ammonium acetate, in 1 M KCI and in 0,01 M CaCl2 after incubation. Ca0Mg 0 CaoMgi Ca|Mg0 Ca.Mg, 1 M neutral ammonium acetate 1. Fincsand 1,23a 5,54° 1,26a 4,46b 2. Fincsand 5,86a 10,40b 6,02a 11,06b 3. Very fincsand 15,99b 19,83d 15,18a 19,1 l c 4. Muddy silt 6,15b 10,1 l d 4,68 a 8,00c 5. Silty clay 10,88b 14,81 d 9,20a 11,90c 6. Sandy clay 24,26a 28,95b 23,74a 26,84b 7. Sandy clay 30,26b 54,62c 46,67a 48,98b 8. Silty clay 34,48b 38,92d 31,78a 35,95c 9. Heavy clay 76,96b 83,08c 72,56a 76,15 b 1 M KCI 1. Fincsand 1,24a 5,20 c 1,17a 4,25 b 2. Fincsand 5,73 a 9,66b 5,62 a 9,23b 3. Very fincsand 14,62a 18,74c 14,18 a 17,72b 4. Muddy silt 4,81a 8,49c 4,39a 7,20b 5. Silty clay 9,58b 13,48 d 8,10 a 10,80c 6. Sandy clay 23,45a 26,96b 22,5 3 a 26,08b 7. Sandy clay 47,8 5 b 50,88° 46,08a 48,86 b 8. Siltyclay 31,64° 35,82d 27,09a 29,75 b 9. Heavy clay 74,18° 77,97d 68,10 a 72,40 d 0,01 M CaCI 2 1. Fincsand 1,26a 4,64° 0,94a 3,48b 2. Fincsand 4.54a 7,72 b 4,69a 7,50 b 3. Very fincsand 12,94b 16,22 d 11,60a 14,53° 4. Muddy silt 4,50b 8,06 d 3,01 a 5,51° 5. Siltyclay 9,18° !2.10 d 6,44a 8,50b 6. Sandy clay 14,22b 16,63d 12,60a 15,00° 7. Sandyclay 31.51b ° 34,31° 27,19a 28,62ab 8. Siltyclay 17,32° 19,63d 14,60a 15,29 b 9. Heavy clay 42,10° 44,75 d 33,75 a 36,50b From the clay soils 0,01 M CaCl 2 seemed to extract to a noticeably smaller degree magnesium than ammonium acetate. In comparison to ammonium acetate the extracting ability of CaCl 2 was perhaps somewhat greater in coarse mineral soils (I—4) and acid silty clay (5) than in clay soils (6—9). Without magnesium fertilization most of the limed soils contained significantly smaller amounts of ammonium acetate extractable magnesium than the unlimed soils (Table 3). The absolute decrease in soil magnesium content caused by liming was greatest in sandy clay (7) 3,6 mg/100 g and heavy clay 4,4 mg/100 g. In relative terms, the greatest decrease in the soil magnesium content by liming was observed in muddy silt (24 %) and in acid silty clay (15 %). In contradistinction to other soils liming seemed to increase to a slight degree the ammonium acetate extractable magnesium content in finesand soils. Liming decreased significantly the amount of 1 M KCI extractable magnesium in silty clays (5 and 8), sandy clays (6 and 7) and heavy clay. The relative decrease in the magnesium content was greatest in sandy days, 1 5 % and 14%, respectively. 131 It should be noted that liming seemed to have no effect on the KCI extactable magnesium content of muddy silt, although the amount of ammonium acetate extractable magnesium decreased significantly. In all soils the CaCl2 extractable magnesium content decreased by liming more than the magnesium extractable in KCI or ammonium acetate. In muddy silt and acid silty clay the magnesium content (CaCl 2) was 38 % and 30 % lower in limed than in unlimed soils. The relative decrease in the ammonium acetate extractable magnesium caused by liming was also greatest in these two soils. Almost all the fertilizer magnesium (4 mg/100 g soil) was extractable in ammonium acetate in unlimed soils, yet the magnesium content of heavy clay increased more than by the magnesium supply. The KCI extractable magnesium increased in nearly all soils with the same amount as the given magnesium, with the exception of sandy clays. In coarse mineral soils 3,1—3,6 mg/100 gof the fertilizer magnesium extracted in CaCl2 and in clay soils 2,3—2,9 mg/100 g. Liming also caused the fixation of fertilizer magnesium in the forms not extractable in ammonium acetate. This was most intense in acid silty clay and sandy clays and weaker in finesand (1), muddy silt and heavy clay. The exchangeable magnesium content of limed sandy clay (7) and heavy clay supplied with magnesium was the same as the magnesium content of untreated soils. Magnesium fertilization seemed to cover the decrease in soil magnesium content caused by liming in these soils. In the other soils magnesium fertilization increased significantly the exchangeable magnesium. In muddy silt, silty clays and sandy clay (7) liming caused about 30 % of fertilizer magnesium to be fixed in forms not extractable in KCI, in other soils the respective figures varied from 7 to 20 %. The KCI extractable magnesium content of silty clay (8) and heavy clay was significantly lower when supplied with lime and magnesium than without treatments. The CaCl 2 extractable magnesium content of silty clay (8) increased by magnesium fertilization only 0,7 mg/100 g and the content of sandy clay (7) 1,4 mg/100 g soil. The respective increase in other soils amounted to 2,1—2,9 mg/100 g soil. After incubation, 17—73 % of the magnesium in limed soils applied in fertilization was extractable in CaCl2 . To limed silty clays and heavy clay, magnesium fertilization did not bring so much magnesium that the CaCl 2 extractable magnesium would have remained at the same level as in unlimed soils. The ammonium acetate extractable calcium content increased in all soils with nearly the amount of calcium supplied in lime (Table 4). All the calcium extracted in ammonium acetate might not come from the soil, but a part could be extracted from calcium carbonate, since the incubation continued only seven weeks. Magnesium fertilization had no effect on the calcium content of limed or of unlimed soils. Liming decreased significantly the ammonium acetate extractable potassium content of the soil with the exception the finesands (Table 4). In the last mentioned soils the potassium content seemed to increase, as was the case also with the magnesium content. In comparison to the potassium content of unlimed soils the relative decrease was greatest in heavy clay, 6,3 %, and in acid silty clay, 2,2 %. The ammonium acetate extractable sodium content seemed to increase significantly in all limed soils (Table 4) The relative increase amounted to 3—30 %, in finesand (1) the sodium content could increase as much as threefold. 132 Table 4. Ammonium acetate (1 M, pH 7) extractable calcium, potassium and sodium contents (mg/100 g soil) and the equivalent ratio Ca/Mg (ammonium acetate extractable) in the soils after incubation. CapMgo CaoMgl Ca|Mg0 Ca.Mg, Ca mg/100 g soil 1. Fincsand 20a 23 a 187 b 184 b 2. Fincsand 131a 134a 217b 216 b 3. Very fincsand 79b 75 a 167c 169c 4. Muddy silt 58 a 59a 404 b 397 b 5. Silty clay 127 a 130a 309 b 310 b 6. Sandy clay 293 a 294a 371 b 372b 7. Sandy clay 230a 227 a 391 b 399 b 8. Silty clay 380a 382 a 47 3b 480 b 9. Heavy clay 371 a 373 a 570 b 5 56b K mg/100 g soil 1. Fincsand 9,4 a 10,2a 10,1 a 10,0a 2. Fincsand 12,5 a 12,5a 12,8a 13,7b 3. Very fincsand 7,2b 7,3b 6,9 a 6,9 a 4. Muddy silt 14,7b 15,2C 14,3a 13,9a 5. Silty clay 18,2b 18,3b 17,8a 17,8a 6. Sandy clay 43,9ab 43,9 ab 42,4a 44,5b 7. Sandy clay 23,Ob 22,9b 21,8 a 21,9a 8. Silty clay 29,6b 29,6b 28,6a 28,I a 9. Heavy clay 44,6 d 44,0C 41,8 b 40,7a Na mg/100 g soil 1. Fincsand 0,8a l,l a 2,5b 2,4b 2. Fincsand 3,7 a 3,6 a 4,6 a 4,7a 3. Very fincsand 3,0a 2,9 a 3,6 b 3,5b 4. Muddy silt 5,la 4,8 a 6,9b 6,9b 5. Silty clay 2,5a 2,5a 3,3 b 3,2b 6. Sandy clay 5,4a 5,4a 6,5b 6,4b 7. Sandy clav 5,i" 5,3 a 6,5b 6,4b 8. Silty clay 4,9a 4,9 a 5,9 b 6,0b 9. Heavyelay 17,6b 17,2 a 18,lc 17,8b Ca/Mg 1. Fincsand 9,8b 2,4a 90,8d 2 5,Oc 2. Fincsand 13,5C 7,8a 21,8 d 11,9b 3. Very fincsand 2,9b 2,4a 6,7 d 5,4° 4. Muddy silt 5,7b 3,5 a 52,7d 30,0C 5. Silty clay 7,l b 5,2 a 20,4d 15,3C 6. Sandy clay 7,4b 5,9a 9,5 d 8,5C 7. Sandy clay 2,8b 2,5 a 5,I C 4.9 C 8. Silty clay 6,7b 6,0 a 9,1 d 8,lc 9. Heavy clay 2,9 a 2,8 a 4,8 C 4,4b The ideal estimate for the equivalent ratio of the ammonium acetate extractable calcium to magnesium may be about s—B. In the untreated soils of this experiment that ratio was high in finesands, and the ratio was low in very finesand, sandy clay (7) and heavy clay. The amount of calcium carbonate that increased the pH of the soils close to 6 increased the ratio Ca/Mg also to a very high level especially in some coarse mineral soils (Table 4). The ratio of calcium to magnesium in lime and 133 magnesium fertilizer was too low to prevent the great increase in the ratio Ca/Mg of these soils. The very finesand, sandy clay (7) and heavy clay favoured the calcium carbonate supply, since the equivalent ratio Ca/Mg was initially low. In sandy clay (6) and silty clay (8) the ratio continued to stay on the ideal range, when the ratio Ca/Mg in calcium and magnesium supplies was about 13, the same as in this experiment. For these soils the applicability of liming agents containing 3—5 % magnesium might prove suitable. The finesands may benefit the supply of dolomitic limestones with about 10 % magnesium. To muddy silt and acid silty clay the dolomitic limestone containing 7—lo % magnesium may bring so much calcium and magnesium that the equivalent ratio could not become too high. Discussion In the clay soils 0,01 M CaCl 2 extractable magnesium amounted to about a half of the ammonium acetate (I M, pH 7) extractable magnesium content. In the coarse mineral soils and in the acid silty clay, resembling coarse mineral soils, a large proportion of the ammonium acetate extractable magnesium seemed to be extractable in CaCl 2 as well. According to WELTE et al. (1960) and FARINA et al. (1980 a) CaCl 2 extracts in relation to ammonium acetate less magnesium from the soils characterized by a higher cation exchange capacity than from soils with low cation exchange capacity. The 1 M KCI extracted less magnesium from acid muddy silt and silty clay than ammonium acetate (1 M, pH 7), although the soils were washed with both solutions in the same way. The reasons for this difference are unknown and will be considered in additional research. In acid soils some of the exchangeable magnesium may be tight on the exchange sites. During incubation some of the fertilizer magnesium in unlimed soils had fixed to not extractable in 0,01 M CaCl 2, while on the other hand ammonium acetate and KCI extracted almost all the magnesium supplied. MOKWUNYE and MELSTED (1974) found in the soils of temperate and tropical origins that less than 10 % of the added magnesium was retained in forms of not extractable in neutral ammonium acetate during 30 days incubation. In a pot experiment performed with the soils of this incubation experiment it was noted that 5—28 % of the fertilizer magnesium was fixed in ammonium acetate not extractable in unlimed very fineasand and silty clays (JOKINEN 1981 b). During a two-year pot experiment the changes in the soil magnesium status may be different than in an incubation experiment of seven weeks. Liming decreased most of all the CaCl 2 extractable magnesium content of the soils, likewise the ammonium acetate extractable magnesium content decreased in nearly all soils. The results of FARINA et al. (1980 a) in a pot experiment with nine acid mineral soils seemed to indicate something to this effect in this incubation experiment. Among others WIKLANDER (1960) and VELEZ et al. (1974) found that the magnesium concentration of the soil solution or the water extractable magnesium content of the soils decreased sharper than the exchangeable magnesium content in limed soils. WIKLANDER (1960) is of the opinion that in 134 limed soils some of the magnesium in soil solution may be dislocated so as to become exchangeable. The relative decrease in the ammonium acetate extractable magnesium content caused by liming seemed to be most intense in soils with a low pH and an abundance in 1 M KCI extractable aluminium. Liming decreased the aluminium content of the soils likewise (HELYAR and ANDERSON 1974, FARINA et al. 1980 a). The reactions between aluminium and magnesium in the soil by raising the pH have been explained in various ways. KINNIBURGH et al. (1976) found freshly precipitated aluminium gels to adsorbe magnesium specifically above pH 6,5 and they assumed that adsorbed magnesium substituted for aluminium in octahedral lay- er of minerals. According to CEIAN et al. (1979) the specific adsorption of magnesium on aluminium oxides or on silicic oxides is possible, since magnesium is able to form MgOH+ -ions whereas calcium can not form respective ion. The adsor- bed magnesium is in an exchangeable form below pH 6 and non-exchangeable abo- ve this pH value. The formation ofAl-Mg compounds not ectractable in neutral am- monium acetate at a high pH may take place in limed soils (HUNSAKER and PRATT 1970) or the formation of ammonium magnesium phosphates in soils with high magnesium content may also cause the decrease of the soil magnesium content (TAYLOR et al. 1965). The high iron content of the soil does not affect the magne- sium, since iron oxides do not adsorb magnesium specifically (KINNIBURGH et al. 1976). The fixation of magnesium not extractable in neutral ammonium acetate took place likewise in soils of a low content in KCI extractable aluminium. From this FA- RINA et al. (1980 a) concluded that the aluminium resources of soil not extract- able in KCI also participate in the specific adsorption of magnesium above pH 6. The decrease in the exchangeable magnesium content of the soil may have a beneficial effect on the magnesium status h. soils with high magnesium resources in that leaching will be avoided (EDEMEADES and JUDD 1980). In soils of low magnesium content the magnesium fixation caused by liming is obvious. With magnesium containing liming agents it is possible to improve the magnesium status of soils provided that the magnesium supplied in this way does not get into fixation. The fate of magnesium carried by the liming agents needs further research work. In the finesand soils liming seemed to increase the neutral ammonium acetate extractable magnesium, potassium and sodium contents, however, the effect of liming was not significant in all cases. These results show a different trend than the effect of liming in the other soils. As to the magnesium content of the finesand soils the results of the incubation experiment confirm those of the pot experiment (JOKINEN 1981 b). According to ALSTON (1966) liming might increase the exchangeable magnesium content of acid coarse mineral soils. The observations of EDMEADES and JUDD (1980) in nine soils yield similar evidence. WIKLANDER (1960) notes that above pH 6 magnesium desoption takes place in the soil, since the ability of hydrogen ions to displace fixed magnesium increases. Most of the fertilizer magnesium (43 %) was in neutral ammonium acetate in a not extractable form in limed sandy clay. In the pot experiment about 30 % of the magnesium supply had been fixed in ammonium acetate not extrable in this soil (JOKINEN 1981 b) and the apparent recovery of fertilizer magnesium by ryegrass was only 1 3 % (JOKINEN 1981 a). 135 In the incubation experiment the relative change of fertilizer magnesium to being not extractable in ammonium acetate was less than in the pot experiment. This may indicate that the effects of liming on the properties of the soils are slow. In muddy silt the results of the pot experiment as well as of the incubation experiment strengthened each other best of all. The fixation caused by liming of the soil and of the fertilizer magnesium to being not extractable in neutral ammonium acetate, does not in all cases decrease the plants growth and the nutrient contents of the yield (MUNNS and FOX 1976, FARINA et al. 1980 b, JAAKKOLA and JOKINEN 1980). The reason for this lies to some extent in the fact that the plants may be able to take up some of the not very soluble sources of the soil magnesium (KAILA and KETTUNEN 1973). The yield losses are possible on coarse mineral soils e.g. when intensive agriculture with great amounts of nitrogen fertilizers is carried out (JOKINEN 1981 a). The liming requirement on the basis of the soil pH has been recommended e.g. by MÄNTYLAHTI and YLÄRANTA (1980). From the results of this incubation experiment and also from those of the pot experiment (JOKINEN 1981 b) it is possible to draw the conclusion that in some soils an exclusive knowledge of the liming rates is not enough. The equivalent ratio of the neutral ammonium acetate extractable calcium and magnesium in the soil may indicate the choice of the type of liming agents. In clay soils the equivalent ratios Ca/Mg are in general lower than the ideal values 5-8. Therefore these soils are more in need of calcium than of magnesium (KERÄNEN and JOKINEN 1964), and the applicability of calcitic limestone may be good. The decrease of the exchangeable magnesium content in the soil should be taken into consideration in the selection of liming agents for soils with low magnesium content and with low cation exchange capacity. The liming agent should contain all the more magnesium the higher the ratio Ca/Mg in the soil. Acknowledgement: I am grateful to the Foundation for Research of Kemira Oy for having received a grant for the completion of this research. References ADAMS, F. & HENDERSON, J. B. 1962. Magnesium availability as affected by deficient and adequate levels of potassium ar.d lime. Soil Sei. Soc. Amer. Proc. 26: 65—68. ALSTON, A. M. 1 966. The influence of N and Mg fertilizers and CaCO* on the absorption of Mg by oats. J. Agric. Sci. 66: 61—66. CHAN, K. Y., DAVEY, B. G. & GEERING, H. R. 1979. Adsorption of magnesium and calcium by a soil with variable charge. Soil Sei. Soc. Amer. J. 43: 301 304. CHRISTENSON, D. R., WHITE, R. P. & DOLL, E. C. 1973. Yield and magnesium uptake by plants as affected by soil pH and calcium levels. Agron. J. 65: 205—206. EDMEADES, D. C. & JUDD, M. J. 1 980. The effects of lime on the magnesium status and equilibria in some New Zealand topsoils. Soil Sci. 129: 1 56—161. FARINA. M. P. W., SUMNER, M. E., PLANK. C.O. & LETZSCH, W. S. 1980 a. Effect ofpH on soil magnesium and its absorption by corn. Comm. Soil Sci. Plant Anal. 1 1: 981—992. - SUMMER, M. E., PLANK, C.O. & LETZSCH, W. S. 1980 b. Exchangeable aluminium and pH as indicators of lime requirement for corn. Soil Sei. Soc. Amer. J. 44; 1036—1041. HELYAR, K. R. & ANDERSON, A. J. 1974. Effects of calcium carbonate on the availability of nutrients in an acid soil. Soil Sei. Soc. Amer. Proc. 38; 341 346. 136 HUNSAKER, V. E. & PRATT, P. E. 1970. The formation of mixed magnesium-aluminium hydroxides in soil materials. Soil Sei. Soc. Amer. Proc. 34: 813—816. JAAKKOLA, A. & JOKINEN, R. 1980. Comparison of fine and coarse limestones in pot and field experiments. Ann. Agric. Fenn. 19: 108—124. JOKINEN, R. 1981 a. Soil magnesium and fertilizer magnesium uptake by ryegrass on nine mineral soils at two ammonium nitrate levels I. Magnesium uptake. Ann. Agric. Fenn. 20: 000—000. (in press) 1981 b. Soil magnesium and fertilizer magnesium uptake by ryegrass on nine mineral soils at two ammonium nitrate levels 11. Magnesium content of soils. Ann. Agric. Fenn. 20: 000—000. (in press) JUO, A. S. R. & UZU, F. O. 1977. Liming and nutrient interactions in two ultisols from southern Nigeria. Plant and Soil 47: 419-430. KAILA, A. 1974. Effect of liming on basic exchangeable cations of soil. J. Scient. Agric. Soc. Finl. 46: 167 174. & KETTUNEN, H. 1973. Magnesium-supplying power of some Finnish mineral soils. J. Scient. Agric. Soc. Eini. 45: 319-324. KERÄNEN, T. & JOKINEN, R. 1964. Magnesiumin puutteen torjuminen magnesiumpitoisuudeltaan erilaisilla kalkkiki vijauhcilla. Referat: Bekämpfung von Magnesiummangel mit Kalksteinmehlen verschiedenen Magnesiumgehaltes. Ann. Agric. Fcnn. 3: 244—2 55. KINNIBURGH, D. G., JACKSON, M. L. & SYERS, J. K. 1976. Adsorption of alkalinen earth, transition, and heavy metal cations by hydrous oxide gels of iron and aluminium. Soil. Sei. Soc. Amer. J. 40: 796 799. MOKWUNYE, A. U. & MELSTED, S. W. 1973. Magnesium fixation and release in soils of temperate and tropical origins. Soil Sci. 1 16: 359—362. MUNNS, D. N. & FOX. R. L. 1976. Depression of legume growth by liming. Plant and Soil 45; 701—705. MÄNTYLAHTI, V. & YLÄRANTA, T. 1980. The estimation of soil lime requirement in soil testing. Ann. Agric. Fenn. 19: 92—99. TAYLOR, A. W., GURNEY. E. L. & FRAZIER, A. W. 1965. Precipitation of phosphate from ammonium phosphate solutions by iron oxide and aluminium hydroxide. Soil Sei. Soc. Amer. Proc. 29: 317—320. VELEZ, J., ZANTUA, M. I. & BLUE, W. G. 1974. Lime induced plant growth depression in an alluvial entisöi from Costa Rica. Soil Sei. Soc. Amer. Proc. 38: 460—464. WELTE, E., WERNER, W. & NIEDERBUDDE, E. A. 1960. Zur Frage der Magnesium-Dynamik im Boden. Trans. 7th Int. Congr. Soil Sei. II: 246—2 52. WIKLANDER, L. 1960. Influence of liming on adsorption and desorption ofcations in soils. Trans. 7th Int. Congr. Soil Sei. II; 283—291. Ms received April 27, 1981 SELOSTUS Kalkituksen vaikutus eräiden kivennäismaiden magncsiumtilaan ja lannoituksena annettuun magnesiumiin Raili Jokinen Helsingin yliopisto, Maanviljelyskemian laitos, 00710 Helsinki 71. Tutkimuksen tarkoituksena oli selvittää CaCO,:na (lab. rcag.) annetun kalkituksen vaikutusta yhdeksän kivennäismaan (pH 3,9—6,1) magncsiumtilaan ja lannoituksena annetun magnesiumin kohtaloon näissä maissa. Maat käsiteltiin kalkilla ja magnesiumsulfaatilla (MgS0 4 ‘7H 2 0), joissa maihin lisättiin kalsiumia ja magnesiumia 100 g maata kohti scuraavat määrät: CanMg,, Ilman Ca ja Mg CaOMg! Ilman Ca + 4 mg Mg Ca|Mg„ 90, 180 tai 360 mg Ca 9O, 180 tai 360 mg Ca + 4 mg Mg 137 Tavoitteena oli kohottaa maiden pH(CaCl2 ) 6ja 6,5 välille. Sen vuoksi käytetyt kalkkimäärät olivat erilaiset eri maille. Hehtaaria kohti laskettuna magnesiumlannoitus vastaa 80 kg Mg ja kalkitukset 5, 10 tai 20 tonnia kalkkikivijauhetta ( 3 5 % neutraloivaa Ca). Maita muhitettiin laboratoriossa aerobeissa oloissa 20 °C va- kiolämpötilassa seitsemän viikon ajan. M uhiteltujen maiden magnesiumpitoisuus määritettiin kolmesta uutteesta 1) I M ammoniumasetaatti, pH 7 2) 1 M kaliumkloridi 3) 0,01 M kalsiumkloridi Kansainvälisissä tutkimuksissa käytetään yleisesti neutraalia ammoniumasetaattia vaihtuvan magnesiumin uuttamiseen maasta. Puskuroimaton kaliumkloridi uuttaa maan omassa pH :ssa vaihtuvana olevaa magnesiumia. Kalsiumkloridiin uuttuva magnesium kuvaa magnesiumin aktiivisuutta (helposti kasvien käytettävissä olevaa magnesiumia). Seitsemässä maassa kalkitus näytti vähentävän 0,01 M kalsiumkloridiin uuttuvan magnesiumin määrää enemmän kuin 1 M kaliumkloridiin tai 1 M neutraaliin ammoniumasetaattiin uuttuvaa magnesiumia. Kalkitut maat sisälsivät ammoniumasetaattiin uuttuvaa magnesiumia 2—24 % vähemmän kuin kalkitsunat- tomat maat. Magnesiumpitoisuuden väheneminen oli runsainta happamissa liejuisessa hiesussa (Litorina maa) ja hiesusavessa. Kalkitsemattomana nämä maat sisälsivät 6,6 ja 2,2 me/100 g maata 1 M kaliumkloridiin uuttuvaa (AJ + HF) ja niiden pH(CaCl2 ) olivat vastaavasti 3,9 ja 4,5. Karkeissa hiedoissa kalkitus näytti lisäävän ammoniumasetaattiin uuttuvaa magnesiumia, mutta lisäys ei ollut merkitsevä. Efektiivisen kationinvaihtokapasiteetin suhteellinen lisääntyminen kalkituksen seurauksena saattoi olla kar- keissa kivennäismaissa suurempi kuin savimaissa. Lannoituksena annetusta magnesiumista oli kalkituissa maissa kalsiumkloridiin uuttuvana 17—73 %, ka- liumkloridiin uuttuvana 67 100 % ja ammoniumasetaattiin uuttuvana 57—100 %. Vaihtuvan (pH 7) kalsiumin ja magnesiumin ekvivalenttisuhde Ca/Mg antanee viitteitä kalkitusaineen va- lintaa varten. Kalkitusaineen tulisi sisältää sitä enemmän magnesiumia mitä korkeampi Ca/Mg on maassa. Ihan- teelliseksi Ca/Mg:n arvoksi on tässä tutkimuksessa otettu useiden tutkijoiden mainitsemat luvut s—B.