Maataloustieteellinen A ikakauskirja Vol. 61: 79—87, 1989 Extractable aluminium, iron and manganese in mineral soils II Extractability by oxalate and pyrophosphate RAINA NISKANEN Department of Agricultural Chemistry, University of Helsinki, SF-00710 Helsinki, Finland Index words: amorphous oxides, complexing agents, soil organic carbon, soil extraction Introduction Acid ammonium oxalate (Tamm 1922, Schwertmann 1964, McKeague and Day 1966) and 0.1 M Na 4P 2 07 (Aleksandrova 1960, McKeague 1967) are conventionally used for the extraction of aluminium, iron and manganese from soil. Amorphous oxides and metals bound to organic matter in soil are dissolved by these solutions. The use of these reagents, however, may cause some problems in analytical work. Abstract. The extractability of aluminium, iron and manganese by 0.05 M oxalate and pyrophosphate was studied in samples of 23 mineral soils. Dilute extractants were studied be- cause conventional reagents may cause problems in analytical work. The mean values for Al, Fe and Mn extracted by conventional Tamm’s oxalate were 67, 81 and 1.5mmol/kg soil, respec- tively. On the average, 0.05 M oxalate solutions at pH 2.9 and 4.2 extracted Al, Fe and Mn amounts that were 103, 113 and 87 % and 72, 82 and 83 % of the amounts extractable by Tamm’s oxalate, respectively. Eeach metal released by 0.05 M oxalates correlated closely with that dissolved by Tamm’s oxalate; the r values ranged from 0.967*** to 0.997***. The mean values for Al, Fe and Mn extracted by 0.1 M Na4P 207 and 0.05 M K 4P 207 were 38, 28 and 0.6 and 33, 29 and 0.6 mmol/kg soil, respectively. The amount of each metal extracted by Na 4P 2 07 correlated closely with that released by K 4P 207 ; the r values ranged from o.B7*** to o.97***. Traditional colorimetric, titrimetric and gravimetric techniques have commonly been superseded by atomic absorption spectro- photometry. Application of this technique may sometimes be hampered by the tendency of the nebulizer and burner slot to clog when solutions of high salt concentration are aspirated. Acid ammonium oxalate has often proved to be especially troublesome in this respect (e.g. Webber et al. 1974, Searly and 79 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=6JNQI4BJASOXoQqv.RZi29SKQEhiZGHMLx7Esxg.3opS7CyWyOsFeMQ-z50E-QW61MXsUpuRg7d8JvR4Cg8spMW31Elu29bK2pSOa9EVBkVI6g4QPKu_OWbXBvsqhMec6TDSM2GfFrx-0j1A_LmUgGAAh8xbew4MlQ6ERFXlo2qQ8SO8326fNPRxVDyp7nTmnkMc4bjg7v5rRA 80 Daly 1977, Simmons and Plues-Foster 1977). Difficulties may partially be overcome by dilution of the solutions to be analyzed. Pyrophosphate is difficult to use as an extrac- tant because of soil dispersion. Especially with clay soils, normal filtration through paper is not enough for clarifying extracts (Sheldrick and McKeague 1975, Schuppli et al. 1983). These difficulties in analytical work should be alleviated by the use of more dilute extrac- tants. A previous paper (Niskanen 1989) showed that the ability of oxalate and pyrophosphate to extract soil aluminium, iron and manganese depends on the pH value, and that the extractability by 0.05 M reagents can reach the same order of magnitude as that by conventional methods. The aim of this paper was to study the possibility of employing 0.05 M oxalate and pyrophosphate solutions instead of the traditional reagents for the ex- traction of aluminium, iron and manganese from soil. Material and methods The material was collected at 14 sampling sites on the Viikki Experimental Farm, University of Helsinki (Nos. I—9)1 —9) and in South Karelia (Imatra) (Nos. 10—14) (Table 1). At sampling sites Nos. I—91 —9 both surface (0—20 cm) and deeper layer (20 —40 cm) sam- ples were taken; at sampling sites Nos. 10—14 only surface samples were taken. The soils were air-dried and ground to pass through a 2-mm sieve. The particle-size distri- bution of the inorganic material in the soil was determined by the pipette method (Elonen 1971), the organic carbon content by the Ai.- ten wet combustion method (Graham 1948). The soil pH was measured in a soil-0.01 M CaCl2 suspension (1:2.5 v/v) (Ryti 1965). The soils were extracted by the methods given in Table 2. Na4 P207 extracts were clarified by the addition of 1 M HCI and then filtration through hard paper, K 4P 2 07 ex- Table 1. Soil samples (a = o—2o0 —20 cm, b = 20—40 cm, V = virgin soil). Soil pH(CaCI : ) Organic C, Particle-size distribution (urn), % No. % < 2 2—20 20—60 60—200 > 200 la 4.6 3.3 37 13 15 30 4 lb 5.2 0.8 39 6 14 38 3 2a 4.3 4.7 36 8 21 34 3 2b 5.0 1.0 26 2 23 42 6 3a 5.9 5.3 58 14 12 13 3 3b 5.6 1.7 45 19 16 17 3 4a V 3.5 9.2 371129 50 4b V 4.1 2.7 251028 55 5a V 4.6 1.5 4163025 26 5b V 4.3 2.0 11 29 41 12 7 6a 4.8 2.4 29 30 20 15 6 6b 5.2 1.4 49 20 11 16 4 7a 4.5 3.4 43 33 18 3 2 7b 4.8 2.6 47 30 18 5 0 8a 5.3 4.4 10 7 15 61 7 8b 5.3 3.0 11 7 17 59 6 9a V 4.4 3.0 22315 77 9b V 4.6 0.8 21735 56 10a V 4.3 6.0 56522 62 11a 5.7 3.8 22 31 27 16 5 12a 5.1 3.6 13 20 27 31 9 13a 4.7 4.7 51 27 11 5 7 14a 5.2 3.2 31 43 13 7 5 x 4.8 3.2 25 16 17 24 18 s 0.6 1.9 19 12 9 16 24 range 3.5—5.9 0.8—9.2 2—58 1—43 3—41 3—61 0—77 81 Table 2. Extraction methods. Extractant pH Extraction Shaking Reference ratio, w/v time, h 1. 0.18 M ammonium oxalate, 0.10 M oxalic acid 3.3 1:20 2 Tamm 1922 2. 0.026 M ammonium oxalate, 0.024 M oxalic acid 2.9 1:20 2 3. 0.041 M ammonium oxalate, 0.009 M oxalic acid 4.2 1:200 3 4. 0.029 M ammonium oxalate, 0.021 M oxalic acid 3.3 1:20 2 5. 0.1 M Na4P,0 7 10 1:20 4 McKbaoue 1967 6. 0.05 M K 4P 207 10 1:100 3 tracts by filtration through 0.2-|im membrane filters. Aluminium, iron and manganese in filtrates were determined by atomic absorp- tion spectrophotometry, iron and manganese with air-acetylene and aluminium with N2O- -flame. The experiment was carried out in duplicate. Results and discussion Extractability by oxalate Aluminium and iron extracted byTamm's oxalate, respectively, were nearly of the same order of magnitude as those extracted by 0.05 Table 3. Extractable aluminium, mmol/kg soil.* Soil 2,3 Al extracted by No. 'Tamm's 0.05 M oxalate 0.05 M oxalate 0.1 M 0.05 M oxalate pH 2.9 pH 4.2 Na 4P 20 7 K 4P 20 7 la 31'' 34d 17' 14" 10» lb 17h 29- 8» 2» 4» 2a 49' 1 51 d 38' 28" 23» 2b ll 1' 12" 5» 4» 4» 3a 1 04-' 92" 70" 52b 44" 3b 63' 68d 27» 30» 26» 4a 55' 51 b ' 41» 47»b 41» 4b 81b 82 h 58» 81 b 79 h 5a 34" 35" 23» 23» 22» 5b 58' 61' 40» 46 h 44» b 6a 53d 54d 37' 28" 21» 6b 52' 54' 34b 15» 11» 7a 79' 1 74' 1 66' 37" 31» 7b 76d 68' 64' 23» 16» 8a 23' 24" 19h 15» 15» 8b 21' 23' 15h 10» 10» 9a 59h 69' 54 h 46» 46» 9b 104" 92" 110" 54» 56» 10a 67' 1 65' 1 57' 46" 35» 11 a 80d 76d 64' 42b 29» 12a 186' 161" 158h 92» 82» 13a 159'' 134' 115»' 108" 74» 14a 78' 73d 53' 40" 30» x 67 64 51 38 33 s 42 34 37 27 23 range 11 186 12—161 5—158 2—loB 4—82 * Each soil tested separately. Values marked with the same letter do not deviate, with 5 % risk. 82 Table 4. Extractable iron, mmol/kg soil.* Soil Fe extracted by No. Tamm's 0.05 M oxalate 0.05 M oxalate 0.1 M 0.05 M oxalate pH 2.9 pH 4.2 Na 4P,07 K4P,0 7 la 34' 43 d 29 h 13» 12» lb 28' 37 d 20" 5» 5» 2a 47 h 59J 55' 26» 28» 2b 11"' 14' 9b 3» 5» 3a 107' 120d 97" 42» 41» 3b 157' 162' 112" 40» 41» 4a 49"1 56" 41" 31» 47"' 4b 44' 55 d 35" 27» 36h 5a 23' 31 d 19" 11» 12» 5b 60d 71' 55' 34» 40h 6a 79' 95 d 68" 27» 30» 6b 93 d 105' 70 1 20" 17» 7a 211'' 192' 174h 42» 50» 7b 223' 202" 213' 38» 40» 8a 140' 144' 121 h 69» 78» 8b 115" 135' 101" 47» 53» 9a 30' 42 d 25" 13» 15» 9b 32 h 39' 31 h 10» 9» 'loa 34' 37' 23" 18» 17» 11a 60-' 61 d 37' 16" 12» 12a 53 d 52 d 36' 24" 20» 13a 159' 124d 113' 55 h 40» 14a 84 d 86 d 59' 23 h 18» x 81 85 67 28 29 s 60 53 52 17 19 range 11—223 14—202 9—213 3—69 5—78 * Each soil tested separately. Values marked with the same letter do not deviate, with 5 % risk. M oxalate at pH 2.9, but higher than those extracted by 0.05 M oxalate at pH 4.2 (Tables 3 and 4). In most samples Tamm's oxalate ex- tracted more manganese than that extracted by dilute oxalates (Table 5). The metals ex- tracted by dilute oxalates correlated closely to those extracted by Tamm's oxalate. Regres- sion equations describing the relationship be- tween extractabilities and corresponding linear correlation coefficients were as follows: that extractable by Tamm's oxalate (Table 6). The relative extractability of aluminium was lower than that of iron and manganese, being at the lowest 43 °?o of the Tamm's oxalate- extractable aluminium (Table 6). In order for the extractability by 0.05 M oxalate to reach the same order of magnitude as that by Tamm's oxalate, the pH of the extractant must be lower than 4.2. The lower extractability by oxalate at pH Al(Tamm) (mmol/kg) = —11.41 + 1.22A1(0xa1. pH 2.9) (mmol/kg) r = 0.992*** Al(Tamm) (mmol/kg) = 10.32 + l.HAl(oxal. pH 4.2) (mmol/kg) r = 0.967*** Fe(Tamm) (mmol/kg) = —13.14 + l.HFe(oxal. pH 2.9) (mmol/kg) r = 0.982*** Fe(Tamm) (mmol/kg) = 5.50 + I.l3Fe(oxal. pH 4.2) (mmol/kg) r = o.9Bl*** Mn(Tamm) (umol/kg) = 55.98 + 1.10Mn(oxal. pH 2.9) (umol/kg) r = 0.984*** Mn(Tamm) (umol/kg) = 83.99 + I.osMn(oxal. pH 4.2) (umol/kg) r = 0.997*** The extractability of metals by 0.05 M 4.2 is in agreement with the results of oxalate at pH 4.2 was commonly < 100 %of McKeague and Day (1966). They found that Table 5. Extractable manganese, pmol/kg soil.* Soil No. Mn extracted by Tamm’s oxalate 0.05 M oxalate 0.05 M oxalate 0.1 M pH 2.9 pH 4.2 Na 4P20 7 la 228a 228» lb 410 408' 2a 419' 1 355 1* 2b 346' 346' 3a 1 092" 850 3b 160d 191 J 4a 1 138' 869" 4b 3 640- 3 986' 5a 301' 282*"' 5b 956d 784' 6a 3 367J 3 367J 6b 1 911' 1 1 531" 7a 410' 346»' 7b 273' 164" 8a 501' 382» 8b 437'- 337' 1 9a I 211' 1 008"' 9b 528'' 497' 1 10a 1 529» 1 222» 11a 4 004' 1 3 640 12a 2 212" 2 184" 13a 2 821' 1 671- 14a 7 490' 6 243" x 1 538 1 343 s 1 753 1 562 range 160—7 490 164—6 243 * Each soil tested separately. Values marked with the same letter do not deviate, with 5 % risk. approximately equal amounts of iron and aluminium, respectively, were extracted by oxalate at pH 2 and 3, but that solution of pH 4.2 extracted somewhat less metals. The solutions of pH 2 and 3 also maintained their initial pH, whereas the solution of pH 4.2 was not buffered strongly enough to maintain a constant pH in extracts of soils rich in iron and aluminium. lb, poor in aluminium. The pH of oxalate was lowered to 2.9 be- cause a preliminary experiment showed that the extractability of iron by 0.05 M oxalate at pH 3.3 was lower than that extractable by Tamm’s oxalate (Table 7). In most soils, the extractability of aluminium and iron by oxalate at pH 2.9, unlike that of manganese, was not lower than the extractability by Tamm’s solution (Table 6). The extractability of aluminium was exceptionally high in soil Extractability by pyrophosphate 0.05 M k 4p 2o 7 260» 118» 273» 346b ' 155" 304b 346b 209» 364' 260b 151» 315- 1 214'- 233» 364b 87b 36» 1221 * 868» 596" 1 01 l h ' 3 559' 837" 1 661 b 173» 137» 242b 824' 346» 513" 3 164' 482» 728b 1 734' 164» 242» 303"' 69» 242b 173" 87» 152" 433b, l 90a 274» 260' 82» 137" 910 b- 301» 637»b 433' 100» 137» 1 300» 1 984 b 1 255» 3 553' 1 766 b 1 183» 2 254 b 2 276b 1 664» 2 340d 1 I83b 698» 7 055' 1 693» 1 365» 1 385 574 604 1 664 697 502 87—7 055 36—2 276 122—1664 Oxalate-extractable metals were not related to soil pH or organic carbon content. Only oxalate-extractable iron correlated weakly with the soil clay content. The linear correla- tion coefficients for the relationship between clay content and iron extracted by Tamm’s solution and by oxalates of pH 2.9 and 4.2 were 0.55**, 0.53* and 0.52*, respectively. In most of the soils, the values of alumi- nium and iron, respectively, did not deviate statistically in both pyrophosphate extractions (Tables 3 and 4), whereas the manganese values deviated in most soils (Table 5). The metals released in two pyrophosphate extrac- tions correlated closely, the regression equa- 83 Table 6. Extractable aluminium, iron and manganese,% of Tamm's oxalate-extraclable. Soil Metals extracted by No. 0.05 M oxalate pH 2.9 0.05 M oxalate pH 4.2 0.1 M Na,P,O, 0.05 M K 4P 2 O, Al Fe Mn Al Fe Mn Al Fe Mn Al Fe Mn la 110 127 100 55 85 114 45 38 52 32 35 120 lb 171 132 100 47 71 84 12 18 38 24 18 74 2a 104 126 85 78 117 83 57 55 50 47 60 87 2b 109 127 100 46 82 75 36 27 44 36 46 91 3a 89 112 78 67 91 111 50 39 21 42 38 33 3b 108 103 119 43 71 54 48 26 23 41 26 76 4a 93 114 76 75 84 76 86 63 52 75 96 89 4b 101 125 110 72 80 98 100 61 23 98 82 46 5a 103 135 94 68 83 58 68 48 46 65 52 80 5b 105 118 82 69 92 86 79 57 36 76 67 54 6a 102 120 100 70 86 94 53 34 14 40 38 22 6b 104 113 80 65 75 91 29 22 9 21 18 13 7a 94 91 84 84 83 74 47 20 17 39 24 59 7b 90 91 60 84 96 63 30 17 32 21 18 56 8a 104 103 76 83 86 86 65 49 38 65 56 55 8b 110 117 77 71 88 60 48 41 19 48 46 31 9a 117 140 83 92 83 75 78 43 25 78 50 53 9b 89 122 94 106 97 82 52 31 19 54 28 26 10a 97 109 80 85 68 85 69 53 130 52 50 82 I la 95 102 91 80 62 89 53 27 44 36 20 30 12a 87 98 99 85 68 102 50 45 103 44 38 75 13a 84 78 59 72 71 83 68 35 42 47 25 25 14a 94 102 83 68 70 94 51 27 23 39 21 18 x 103 113 87 72 82 83 55 38 39 49 41 56 s 17 16 14 15 12 16 20 14 28 20 21 29 range 84—171 78—140 59—119 43—106 62—117 54—114 12—100 17—63 9—130 21—98 18—96 13—120 84 Table 7. Aluminium and iron extracted by 0.05 M oxalate pH 3.3, % of Tamm’s oxalate-extractable. Soil No. Al Fe la lb 2b 3b 94 88 135 84 99 74 101 75 12a 68 69 tions and corresponding linear correlation coefficients being as follows: AI(Na4P2 O 7 ) (mmol/kg) = 0.99 + 1.14A1(K4P 207) (mmol/kg) Fe(Na 4P 2O 7 ) (mmol/kg) = 3.14 + 0.84Fe(K4P207) (mmol/kg) Mn(Na4P 2 O 7) (umol/kg) = —157 + 1.21Mn(K4P 2 07 ) (|xmol/kg) Pyrophosphate-extractable metals did not correlate statistically significantly with soil pH or clay content. In contrast, the pyrophos- phate-extractable metals correlated with the oxalate-extractable metals. Regression equa- tions describing the relationship between metals extracted by Tamm’s oxalate and pyrophosphates and corresponding linear correlation coefficients were as follows: Al(Tamm) (mmol/kg) = 13.37 + 1,40A1(Na4P2 O7) (mmol/kg) Al(Tamm) (mmol/kg) = 16.31 + 1.55A1(K4 P 207 ) (mmol/kg) Fe(Tamm) (mmol/kg) = 5.39 + 2.76Fe(Na4P 207) (mmol/kg) Fe(Tamm) (mmol/kg) = 18.24 + 2.18Fe(K4P207 ) (mmol/kg) Mn(Tamm) (umol/kg) = 574 + 1.68Mn(Na4P 2 07 ) (umol/kg) Mn(Tamm) (umol/kg) = 27.97 + 2.50Mn(K4P2 07) (umol/kg) The metals extracted by pyrophosphate, considered to describe the fraction bound by organic matter in soil (McKeague et al. 1971) were, on the average, 38—56 % of the Tamm’s oxalate-extractable metals (Table 6). The absolute values of pyrophosphate-extractable metals did not significantly correlate with the organic carbon content in soil. However, there was a low correlation between the organic car- bon content and metals expressed as the per- centages of Tamm’s oxalate-extractable me- tals. The linear correlation coefficients for the relationship between soil organic carbon con- tent and the percentages of K 4P 2(D7-extract- able iron and Na4P207-extractable iron and aluminium were 0.49*, 0.54** and 0.47*, respectively. In pyrophosphate extracts of clay soils, metals are not exclusively in a dissolved form, but are also present in suspended material which is difficult to remove. This material may be fine particulate amorphous material, or it may have been formed by coagulation of solutes in the pyrophosphate extracts (Bascomb 1968, McKeague and Schuppli 1982). The methods used for clarifying of pyrophosphate extracts are high-speed cen- r = 0.968*** r = 0.945*** r = 0.872*** trifugation (McKeague 1967) and the addition of Superfloe, a flocculating agent, followed by centrifugation at low speed (Sheldrick and McKeague 1975). The study of Schuppli et al. (1983) shows that centrifugation at high speed or at low speed with Superfloe is inade- quate to sediment suspended material com- pletely. Adding a salt, such as Na 2S0 4, is not effective at low concentration, and at high r = 0.892*** r = 0.837*** r = 0.756*** r = 0.670*** r = 0.669*** r = 0.717*** concentration it appears to precipitate dis- solved metals. Ultrafiltration of the cen- trifugates through 0.025-pm filters removes particulate material in a simple and effective way. In this study, pyrophosphate extracts were cleared by precipitation of suspended clay and organic matter with acid or filtration through 0.2-pm filters. The latter method seems to be more certain, as acidification of extracts may dissolve metals from suspended material or, on the other hand, metals may partially re- main in precipitates. K 4P 2 Oj, used by Bascomb (1968), was used as an extractant because it was thought that 85 86 peptization of soil may be less than if Na4P207 were used. This opinion was based on the fact that the hydration sphere of K + -ion is smaller than that of Na + -ion. However, lowering the concentration of pyrophosphate from 0.1 M to 0.05 M hardly reduced disper- sion of soil. According to Elonen (1971), 0.05 M concentration of Na 4P 207 is high enough for peptization of soil in particle-size analysis. References Aleksandrova, L.N. 1960. The use of sodium pyro- phosphate for isolating free humic substances and their organic-mineral compounds from the soil. Soviet Soil Sci. 2: 190—197. Bascomb, C.L. 1968. Distribution of pyrophosphate-ex- tractable iron and organic carbon in soils of various groups. J. Soil Sci. 19: 251 —268. Elonen, P. 1971. Particle-size analysis of soil. Acta Agr. Fenn. 122: 1—122. Graham, E.R. 1948. Determination of soil organic matter by means of a photoelectric colorimeter. Soil Sci. 65: 181—183. McKeague, J.A. 1967. An evaluation of 0.1 M pyro- phosphate and pyrophosphate-dithionitein compar- ison with oxalate as extractants of the accumulation products in Podzols and some other soils. Can. J. Soil Sci. 47: 95—99. , Brydon, J.E. & Miles, N.M. 1971. Differentiation of forms of extractable iron and aluminium in soils. Soil Sei. Soc. Amer. Proc. 35: 33—38. & Day, J.H. 1966. Dithionite- and oxalate-extrac- table Fe and Al as aids in differentiating various classes of soils. Can. J. Soil Sci. 46: 13—22. & Schuppli, P.A. 1982. Changes in concentrations of Fe and Al in pyrophosphate extracts of soil and com- position of sediment resulting from ultracentrifuga- tion in relation to spodic horizon criteria. Soil Sci. 134: 265—270. Niskanen, R. 1989, Extractable aluminium, iron and manganese in mineral soils. I Dependence of extrac- tability on the pH of oxalate, pyrophosphate and EDTA extractants. J. Agric. Sci. Finl, 61: 73—78. Ryti, R. 1965. On the determination of soil pH. J, Scient. Agric. Soc. Finl. 37: 51 —60. Conclusion It seems possible to employ oxalate and pyrophosphate extractants, which are more dilute than conventional reagents. The amounts of metals released by dilute and traditional reagents are closely correlated. In general, extraction methods do not give absolute contents of elements. For example, the amounts extracted increase as the extrac- tion time increases. However, the results ob- tained with a given method are valuable for soil comparisons. Schuppli, P.A., Ross, G.J. & McKeague, J.A. 1983. The effective removal of suspended materials from pyrophosphate extracts of soils from tropical and tem- perate regions. Soil Sci. Soc. Am. J. 47; 1026—1032. Schwertmann, U. 1964. Differenzierung der Eisenoxide des Bodens durch photochemische Extraktion mit saurer Ammoniumoxalat-Lösung. Z. Pflanzenernähr. Diing. Bodenk. 105: 194—202. Searle, P.L. & Daly, B.K, 1977. The determination of aluminium, iron, manganese and silicon in acid oxalate soil extracts by flame emission and atomic absorption spectrophotometry. Geoderma 19: I—lo. Sheldrick, B.H. & McKeague, J.A. 1975. A comparison of extractable Fe and Al data using methods followed in the U.S.A. and Canada. Can. J. Soil Sci. 55: 77—78. Simmons, W.J. & Plues-Foster, L.A. 1977. Improved method of analysing difficult soil extracts by flame atomic absorption spectrometry application to mea- surement of copper in ammonium oxalate extracts. Aust. J. Soil Res. 15: 171—175. Tamm, O. 1922: Eine Methode zur Bestimmung der anor- ganischen Komponente des Gelkomplexes im Boden. Statens Skogsförsöksanstalt, Medd. 19: 387—404. Webber, M.D., McKeague, J.A., Raad, A.T., DeKiMPE, C.R., Wang, C., Haluschak, P., Stonehouse, H.8., Pettapiece, W.W., Osborne, V.E. & Green, A.J. 1974. A comparison among nine Canadian laborato- ries of dithionite-, oxalate-, and pyrophosphate-ex- tractable Fe and Al in soils. Can. J. Soil Sci. 54: 293—298. Ms received January 12, 1988 3 SELOSTUS Kivennäismaiden uuttuva alumiini, rauta ja mangaani Il Uutluvuus oksalaatti- ja pyrofosfaatti- liuoksilla Raina Niskanen Helsingin yliopisto, Maanviljelyskemian laitos, 00710 Helsinki Koska oksalaatti- ja pyrofosfaattiuutteiden analysoin- nissa esiintyy vaikeuksia, tutkittiin tavanomaista laime- ampien uuttoliuosten käyttöä. Kivennäismaiden alumii- nia, rautaa ja mangaania uutettiin 0,05 M oksalaatti- ja pyrofosfaattiliuoksilla sekä vertailuliuoksilla: Tammin oksalaatilla ja 0,1 M natriumpyrofosfaatilla. Tammin oksalaatilla uuttui alumiinia, rautaa ja mangaania kes- kimäärin 67, 81 ja 1,5mmol/kg maata. Keskimääräinen alumiinin, raudan ja mangaanin uuttuvuus 0,05 M ok- salaatilla pH 2,9 ja 4,2 oli 103, 113 ja 87 sekä 72, 82 ja 83 % Tammin oksalaatilla uuttuvasta. Kunkin metallin uuttuvuudet Tammin oksalaatilla ja 0,05 M oksalaateil- la korreloivat r;n arvojen vaihdellessa o,967***;stä o,997***:ään (n = 23). Alumiinia, rautaa ja mangaania uuttui 0,1 M natriumpyrofosfaatilla ja 0,05 M kalium- pyrofosfaatilla keskimäärin 38, 28 ja 0,6 sekä 33, 29 ja 0,6 mmol/kg maata. Kunkin metallin uuttuvuudet näil- lä liuoksilla korreloivat r:n arvojen vaihdellessa o,B7***:stä o,97*»»:ään. 87