JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND Maataloustieteellinen Aikakauskirja Vol. 58: I—7, 1986 Estimation of cation-exchange capacity in routine soil testing RAINA NISKANEN and ANTTI JAAKKOLA University of Helsinki, Department of Agricultural Chemistry SF-00710 Helsinki, Finland Abstract. The efficiency of the soil testing method used in Finland forpredicting the effective cation-exchangecapacity was studied in a material of 430 topsoil samples. The effective cation- exchange capacity was estimated 1)by summation of exchangeableCa, Mg and acidity displaced by unbuffered 1 M KCI and 2) by summation of exchangeable Ca, Mg, K and Na displaced by neutral 1 M ammonium acetate and exchangeable acidity. In soil testing, Ca, Mg and K were extracted by acid ammonium acetate and soil pH measured in water-suspension. The estimates of the effective CEC were highly correlated and dependenton the clay and organic carbon content and pH(CaCl 2) of the soil, the coefficient of multiple determination being over 80 Vo. Exchangeable Ca was the dominating cation. The proportion of Ca of the effective CEC was about 80 Vo. Acid ammonium acetate-extractable Ca together with pH(H 20) explained over 80 % of the variation in the effective CEC. For the whole material consisting of mineral soils with great variations in texture, organic carbon content and properties under evaluation, the regression equation predicting the effective CEC (KCI method) was CEC(mvalZkg) = 309—56.8pH(H2 0) + o.oBsCa(mg/l). Only 16 % of the estimates of the effective CEC calculated with this regres- sion equation deviated more than 15 % from the measured values. Index words: exchangeable Ca, Mg, K, Na, exchangeableacidity, effective cation-exchange capacity, soil pH, soil testing Introduction In Finnish soil testing, lime requirement has been estimated on the basis of pH(H 20) and acid ammonium acetate-extractable Ca. Ac- cording to Mäntylahti and Yläranta(l9Bo), however, soil pH alone gives a better estimate. The content of extractable Ca in soil cannot be used as an index of liming requirements as long as the cation-exchange capacity and base saturation vary. On the other hand, ex- changeable calcium contents together with acidity could estimate cation-exchange capa- city of soil. The aim of this study was to examine the relationship between estimates of effective cation-exchange capacity of mineral soils and the possibility of predicting them by soil testing. 1 https://www.c-info.fi/en/info/?token=LzLoK6bNjeyvuZ9m.IkpeBRdvwyS0Dyr3DbzBPA.q8oDfQoaZUIXv0h1ilxyk723qLaO26R8VP7x9NUb3ATAe2KEk-tqggEJ59qc3q5McyDZurQO1_e1kgjcqeE39PA5O7WpVJELiOK06ZlpnZQwiLPhdXUXfUl2XUibBKJUMZ2118GcYMR_e6uX90qjRkFETm6XhozdQ2cmSqjo5mbMunJq9d59IYsdvMIN5Oc Material and methods The material consisted of 430 plough layer (0—25 cm) samples from the agricultural area of the Viikki Experimental Farm. The soil characteristics have been described previously by Jokinen (1983, 1984) and Niskanen and Jaakkola(1985). The samples were air-dried and ground to pass a 2-mm sieve. On the ba- sis of the particle-size distribution determined by the pipette method (Elonen 1971), the material consisted of 230 clay soils with a clay content > 30 % and 200 coarser soil samples with a clay content < 30 % (Table 1). The pH of the soil was measured in a soil-0.01 M CaCl 2 suspension (1:2.5) (Ryti 1965). The mean pH of the coarser soils was 0.3 pH units higher than that of clay soils (Table 1). The organic carbon content of the soil determined by a modified (Graham 1948) Alten’s wet combustion method was on the average 1.5 % higher in clay soils (Table 1). Exchangeable Ca and Mg were extracted from 10 g soil by four successive treatments with 50 ml of neutral 1 M ammonium acetate and 50 ml 1 M KCI and determined by atom- ic absorption spectrophotometry. Exchange- able K and Na were extracted with neutral 1 M ammonium acetate and determined by flame photometry. The exchangeable acidity was displaced with 1 M KCI and titrated with 0.01 M NaOH (Yuan 1959). Two estimates for the effective cation-exchange capacity (CEC) were deter- mined according to Kaila (1971 a, 1972). The effective CECI was estimated by summation of exchangeable Ca, Mg and acidity displaced by 1 M KCI. The effective CEC2 was esti- mated by summation of exchangeable Ca, Mg, Na and K extracted by neutral 1 M am- monium acetate with exchangeable acidity displaced by unbuffered 1 M KCI. The pH of the soil-H20 suspension (1:2.5 v/v) and Ca, Mg and K extracted withacid ammonium ace- tate (0.5 M acetic acid, 0.5 M ammonium ace- tate, pH 4.65, ratio 1:10 v/v) (Vuorinen and Mäkitie 1955) were determined at a commer- cial soil testing laboratory (Viljavuuspalvelu Oy). Results The effective CECI averaged 150 mval/kg soil in clay soils (range 74—250 mval/kg soil) and 108 mval/kg soil in coarser soils (range 43—288 mval/kg soil) (Table 1). On the average, more than 80 % of the effective CECI was saturated with exchangeable Ca, 10 ®/o with exchangeable Mg and less than 10 ®7o with exchangeable acidity (Table 2). Exchangeable Ca was rather closely corre- lated with calcium extracted by the routine soil-testing method (r = o.74***). So was exchangeable magnesium with extractable magnesium (r = o.B3***). The variation in the sum of KCI-extractable calcium and mag- nesium was fairly well explained by acid am- monium acetate-extractable calcium (R 2 = 0.66, n = 430). The relationship between exchangeable acidity and soil pH was curvilinear, but the logarithmic values of exchangeable acidity were linearly correlated with soil pH. With pH(H 20) as an independent variable, the re- gression equation for the whole material (n = 430) was log(acidity) = 4.66—0.68 pH(H2 0), R 2 = 0.83. The dependence of the effective CECI on soil properties was studied using clay and silt content (%), organic carbon content (*Vo) and pH(CaCl2) as independent variables in the regression analysis. Clay content, organic car- bon content and pH(CaCl2) together ex- plained 83.4 % of the variation in the effec- tive CECI of the whole material, the regres- sion equation being CECI (mval/kg) = —227 + I.Bsclay-% + 45.6pH + 11.20rg.C- -%. The silt content was an insignificant ex- plainer. The content of clay fraction explained 67.5 %, organic carbon content 62.9 ®/o and pH(CaCI 2 ) 65.4 % of the variation in the effective CECI, when the effect of the other two independent variables was eliminated. The sum of exchangeable cations extracted by neutral 1 M ammonium acetate averaged 2 3 161 mval/kg soil in clay soils (range 55— 303 mval/kg soil) and 125 mval/kg soil in coarser soils (range 49—329 mval/kg soil) (Table 1). The effective CEC2 estimated by summation of exchangeable acidity displaced by unbuffered 1 M KCI and exchangeable cat- ions extracted by neutral 1 M ammonium ace- tate averaged 172 mval/kg soil in clay soils (range 94—305 mval/kg soil) and 129 mval/kg soil in coarser soils (range 55—333 mval/kg soil). Table 1. Soil characteristics. On the average, 75 % of the effective CEC2 was saturated with exchangeable Ca in clay soils (range 21—92 %) and 81 % in coarser soils (range 43—93 %). The proportion of Mg, K and Na in the saturation of the effec- tive CEC2 was only slightly higher in clay soils than in coarser soils. In the whole material, on the average 10 % of the effective CEC2 was saturated with Mg (range 3—34 %), 5.3 °/o with K (range 0.6—22 %) and 1.2 % with Na (range 0.4—8.5 %). The proportion All soils Clay soils (n = 230) Coarser soils (n = 200)(n = 430) x s range x s range x s range pH(CaCl2 ) 5.3 0.6 4.0—6.8 pH(H2 0) 5.8 0.5 4.2—7.1 Org.C, % 5.2 2.2 1.8—14.6 Clay (< 0.002 mm), % 31 3 6—65 Silt (0.002 0.02 mm), % 17 8 3—43 Coarser fractions 22 7 9—43 13 6 3—37 38 9 20—59 69 10 40—91(0.02 —2 mm), <7o 52 18 20—91 Exchangeable cations (mval/kg soil) extracted by 1 M KCI: Ca 109 36 0—257 V.109 36 0—257 122 35 27—237 93 29 0—257 Mg 14 11 0—72 17 13 4—72 II 6 0—44 Acidity 8 10 I—B2 11 11 1—66 5 7 I—B2 Sum of cations = Effective CECI 131 38 43—288 150 33 74—250 108 30 43—288 Exchangeable cations (mval/kg soil) extracted by neutral 1 M ammonium acetate: Ca 119 39 25—292 131 38 25—280119 39 25—292 131 38 25—280 105 35 38—292 Mg 16 12 3—79 19 14 5—79 12 5 3—31 K 8 4 1—37 9 4 3—37 6 3 I—2l Na 1.81.9 0.4—18.7 2.32.4 0.6—18,7 1.30.6 0.4—5.5 Sum of cations 144 45 49—329 161 43 55—303 125 38 49—329 Effective CEC2 mval/kg soil 152 43 55—333 172 36 94—305 129 37 55—333 Cations (mval/1 soil) extracted by acid ammonium acetate: Ca 89 28 14—193 93 31 14—185 85 24 35—193 Mg 14 13 2—154 16 15 3—79 11 11 2—154 K 6 3 1—32 6 3 2—32 5 2 I—l 6 Sum of cations 108 37 27—274 115 42 27—224 101 30 42—274 Table 2. Exchangeable cations extracted by 1 M KCI, % of effective CECI. All soils (n = 430) Clay soils (n = 230) x s range x s range Coarser soils (n = 200) Ca Mg 83 10 0—94 10 7 0—54 7 9 0.4—100 80 10 26—94 11 7 3—37 9 10 0.4—63 x s range Acidity 85 9 0—95 10 6 0—54 5 8 0.6—100 5.20.6 4.0—6.8 5.50.5 4.5—6.8 5.70.5 4.2—7.1 6.00.5 4.8—7.1 5.92.2 2.5—14.4 4.42.0 1,8—14.6 41 6 30—65 19 6 6—30 of exchangeable acidity averaged 7.5 % in clay soils (range 0.3—55 %) and 3.9 % in coarser soils (range 0.5—52 %). Clay content, organic carbon content and pH(CaCl 2) together explained 84.4 %of the variation in the effective CEC2, the regression equation being CEC2 (mval/kg) = —296 + 1.97c1ay-% + 60.6pH + 12.50rg.C-%. The clay content explained 66.6 %, pH(CaCl2) 73.8 % and organic carbon content 64.1 % of the variation in the effective CEC2, when the effect of the other two independent variables was eliminated. The values of the effective CECI were about 85 % of the effective CEC2 (Table 1), because exchangeable K and Na were not included in the CECI, and more Ca was extracted with neutral ammonium acetate than with KCI. The effective CECI and CEC2 were highly correlated (r = o.96***, n = 430). The sum of Ca, Mg and K extracted by acid ammonium acetate averaged 115 mval/1 soil in clay soils (range 27—224 mval/1 soil) and 101 mval/1 soil in coarser soils (range 42 — 274 mval/1 soil) (Table 1). In the whole mate- rial, 83 % of the cation sum, on the average, was saturated with Ca (range 41—94 %). The proportion of Mg averaged 11 % (range 4—56 %) and that of K 6 % (range 1— 27 %). Clay and silt content, organic carbon content and pH(CaCl 2 ) explained 86.8 % of the cation sum, the regression equation being cation sum (mval/1) = —264 + 1.76c1ay- % I.o3silt-% + 60.2pH + 3.1 lorg.C-%. The content of clay fraction explained 65.6 %, silt content 19.0 %, pH(CaCl 2 ) 80 % and organic carbon content 14.3 % of the variation in the cation sum, when the effect of the other three independent variables was eliminated. The sum of cations extracted with acid ammonium acetate was not very closely correlated with the estimates of effec- tive CEC. The correlation coefficient with CECI was r = o.6s*** (n = 430). The usability of pH(H 20) and Ca, Mg and K extracted by acid ammonium acetate in pre- dicting the effective CEC was tested with clay soils, coarser soils and the whole material. The sum of Ca, Mg and K together with pH(H2 0) explained the variation in the effective CEC as follows: clay coarser all soils soils soils effective CECI 63.0 % 63.2 % 72.3 % effective CEC2 68.4 % 68.9 % 74.1 % The coefficients of determination slightly increased when K was omitted from the sum of cations. The sum of Ca and Mg together with pH(H 2 0) explained the variation in the effective CEC as follows: clay coarser all soils soils soils effective CECI 69.3 % 65.0 % 74.8 % effective CEC2 71.5 % 70.0 % 75.3 % The highest values of the coefficient of determination were obtained by using acid ammonium acetate-extractable Ca instead of cation sum as an independent variable. With Ca and pH(H20) as independent variables explaining the variation in the effective CECI, the coefficients of determination and cor- responding regression equations were as follows: clay soils 81.6 % CECl(mval/kg) = 274 —47.6 pH + I.sBCa(mval/l) coarser soils 75.8 % CECl(mval/kg) = 251 —44.2 pH + I.43Ca(mval/l) all soils 82.6 °/o CECl(mval/kg) = 309 —56.8 pH + I.7oCa(mval/l) With the effective CEC2 as a dependent corresponding regression equations were as variable, the coefficients of determination and follows: clay soils 80.4% CEC2(mval/kg) = 242 —38.4 pH + I.s9Ca(mval/l) coarser soils 84.5 °7o CEC2(mval/kg) = 223 —41.2 pH + I.79Ca(mval/l) all soils 84.0 % CEC2(mval/kg) = 292 —52.9 pH + I.BBCa(mval/l) 4 5 The partial correlation coefficients for the CEC2 (2), pH(H 2Q) (3) and acid ammonium relation between the effective CECI (1) or acetate-extractable Ca (4) were as follows: r 13.4 r 14.3 r23.4 r24.3 clay soils —o.69*** o.BB*** _o.s6*** o.B4*** coarser soils —o.72*** o.B7*** —o.7o*** o.92*** all soils —o.Bl*** o.9l*** _o.76*** o.9l*** Omitting pH(H 20) from the regression analysis decreased the coefficient of determi- nation considerably. With acid ammonium acetate-extractable Ca as the only independent variable, 50.2 % of the variation in the effec- tive CECI for the whole material was ex- plained. Theoretically it was justified to test the re- lationship between effective CEC, pH(H 20) and acid ammonium acetate-extractable Ca also with a regression model in which all variables were logarithmic. However, this model was not superior to the model tested before. According to the logarithmic model, the relationship between the effective CECI, pH(H zO) and Ca in the whole material was described by the equation IogCECI = 1.12 + l.OSlogCa —0.19pH, R 2 = 0.75. The coefficients of determination for clay and coarser soil groups obtained with Ca and pH(H 2 Q) as independent variables did not deviate very much from each other. Therefore the examinationof the material as a whole was appropriate. The variation in the estimates of the effective CEC was explained equally well. The measured values of the effective CECI were compared with the values calculated ac- cording to theregression equation CEClfmval/ kg) = 309 —56.8 pH + I.7oCa(mval/l). The relationship between measured and predicted values is presented in Figures 1 and 2. The pro- portion of samples with the predicted value deviating more than 15 % from the measured value was 16 % of the whole material. This proportion included 11 °7o of the clay soil samples and 22.5 % of the coarser soil samples. In clay soils, the deviation did not exceed 30 % of the measured value. Coarser soil samples with the predicted value much below the measured value (No. I—3)1 —3) were Fig. 1. Relationship between measured effective CECI (Ca +Mg + acidity) and its estimate calculated on the basis of soil testing data (Ca +pH) in coarse mineral soils. Fig. 2. Relationship between measured effective CECI (Ca + Mg + acidity) and its estimate calculated on the basis of soil testing data (Ca+pH) in clay soils. characterized by high clay and organic carbon content. In clay soils the sample with the greatest underestimation of the measured value (No. 9) was characterized by high or- ganic carbon content. Samples with the pre- dicted value much above the measured value (No. 4—B) were characterized by low or mod- erate clay and organic carbon content. The pH(H 2 0) of these soils were 6.0—7.0 and in two cases (No. 7 —B) the content of acid am- monium acetate-extractable Ca was high, over 160 mval/1. It is possible that some undis- solved calcium carbonate existed in the soil. Discussion Although the material was collected from a restricted area, it was characterized by rela- tively great variations in soil properties. Under these circumstances it is justified to consider the material quite suitable for the present examination. It has been shown earlier that the cation- exchange capacity of Finnish mineral soils is largely dependent on clay and organic carbon content (Heinonen 1960, Marttila 1965, Jokinen 1984) together with soil pH (Kaila 1971 a, b). In the study of Kaila (1971 b), the three variables together explained 83 % of the variation in the effective cation-exchange ca- pacity estimated as the sum of exchangeable Ca, Mg and acidity displaced by unbuffered KCI. The result is in good agreement with the results obtained in this study. However, in the material (n = 230) of Kaila (1971 b), or- ganic carbon content was a lesser explainer as compared with the present material with higher mean content and wider range of or- ganic carbon and smaller range of pH(CaCl2). The observation of Kaila (1972) that ex- changeable Ca and Mg together saturate on the average 80—90 % of the effective CEC of cultivated soils was manifested also in this study. The proportion of exchangeable acidity was of minor importance in most soils. The average ratio of exchangeable Ca to Mg was about 7 in clay soils and nearly 9 in coarser soils. In the study of Kaila (1972), the ratio in sand and fine sand soils was about 9 and in clay soils (clay-% < 60) about 4. According to Schmid (1965), the ratio of Ca to Mg would be s—B5 —8 to 1. The average ratio of ex- changeable Mg to K was about 2 both in clay soils and in coarser soils. The average ratio of exchangeable K to Na was higher in coarser soils than in clay soils, the values being 4.6 and 3.9, respectively. In the study of Kaila (1972), the ratio of Mg to K was 2—B and the ratio of K to Na 2—2.8. On the basis of soil testing, the cation- exchange capacity of soil was to some extent predictable. The variation in the effective CEC was best explained by pH in soil-water suspension and Ca extracted by acid ammo- nium acetate. Indeed, additional variation can be caused by the fact that cation-exchange ca- pacity was expressed on a weight basis and acid ammonium acetate-extractable Ca on a volume basis. Using the sum of Ca and Mg or Ca, Mg and K extracted by acid ammonium acetate instead of Ca did not increase the coef- ficient of determination. This was largely due to the fact that K and Mg were only minor components of CEC. The effective CEC was adequately pre- dictable by a regression equation in which pH(H 2 0) and acid ammonium acetate-ex- tractableCa were independent variables. The same equation could be applied to all mineral soils. When Ca is expressed as mg/1, the equa- tion takes the form CEC(mvalZkg) = 309 56.8pH(H2 0) + o.oßsCa(mg/l). Most of the material was such that the predicted CEC value did not deviate more than 15 % from the measured value. Some characteristics com- mon to the samples with a great deviation were observed. High content of organic carbon, e.g., seemed to be associated with a great underestimation of CEC. The immediate reason in this case might be the smaller bulk density which affects the relationship between values given on weight and volume basis. 6 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. Heinonen, R. 1960. Über die Umtauschkapazität des Bodens und verschiedenen Bodenbestandteile in Finn- land. Z. Pflanzenern. Diing. Bodenk. 88: 49—59. Jokinen,R. 1983. Variability of topsoil properties at the southern coast of Finland and the number of soil samples needed for the estimation of soil properties. J. Scient. Agric. Soc. Finl. 55: 109—117. —, 1984. Comparison of and correlation between the characteristics of agricultural topsoil and subsoil at the southern coast of Finland. J. Agric. Sci. Finl. 56: 245—254. Kaila, A. 1971 a. Effective cation-exchange capacity in Finnish mineral soils. J. Scient. Agric. Soc. Finl. 43: 178—186. —, 1971 b. Über den Anteil organischer Substanz an der Austauschkapazität von Mineralböden in Finnland. Spomenica uz 70. god, prof. Gracanina, Zagreb, p. SELOSTUS Kationinvaihtokapasiteetin likiarvon laskeminen viljavuustutkimuksen perusteella Raina Niskanen ja Antti Jaakkola Helsingin yliopisto, Maanviljelyskemian laitos, 00710 Helsinki Tutkimuksessa selviteltiin, voidaanko viljavuustutki- muksessa määritettävien happamaan ammoniumasetaat- tiin uuttuvien kalsiumin, magnesiumin ja kaliumin pitoi- suuksien sekä maa-vesisuspensiosta määritetyn pH:n avul- la laskea likiarvo maan efektiiviselle kationinvaihtokapa- siteetille. Aineisto käsitti 430kivennäismaiden muokkaus- kerroksesta otettua näytettä. Efektiivinen kationinvaih- tokapasiteetti määritettiin 1 M kaliumkloridilla vaihtuvan kalsiumin, magnesiumin ja happamuuden summana se- kä vaihtuvan happamuuden ja neutraalilla 1 M ammo- niumasetaatilla uuttuvan kalsiumin, magnesiumin, ka- liumin ja natriumin summana. Molemmilla menetelmillä saadut efektiivisen kationin- vaihtokapasiteetin arvot korreloivat voimakkaasti keske- nään. Saveksen ja orgaanisen hiilen pitoisuus yhdessä 53—56. —, 1972. Basic exchangeable cations in Finnish mineral soils. J. Scient. Agric. Soc. Finl. 44: 164—170. Marttila, U. 1965. Exchangeable cations in Finnish soils. J. Scient. Agric. Soc. Finl. 37: 148—161. Mäntylahti, V. & Yläranta, T. 1980. The estimation of soil lime requirement in soil testing. Ann. Agric. Fenn. 19: 92—99. Niskanen, R. & Jaakkola, A, 1985. Comparison of analytical methods in testing soil fertility. J. Agric. Sci. Finl. 57: 183—194. Ryti, R. 1965. On the determination of soil pFI. J. Scient. Agric. Soc. Finl. 37: 51 —60. Schmid, G. 1965. Einfluss der Basensättigung auf die Bodenfruchtbarkeit. Landw. Forsch. 28: 97—107. Vuorinen. J. & Mäkitie, O. 1955. The method of soil testing in use in Finland. Agrogeol. Pubi. 63; 1—44. Yuan.T.L. 1959. Determination of exchangeablehydro- gen in soils by a titration method. Soil Sci. 88: 164—167. Ms received November 6, 1985 pH(CaCl 2 ):n kanssa selitti yli 80 % efektiivisen kationin- vaihtokapasiteetin vaihtelusta. Vaihtuvan kalsiumin kes- kimääräinen osuus efektiivisestä kationinvaihtokapasitee- tista oli noin 80 %. Happamalla ammoniumasetaatilla uuttuva kalsium yh- dessä maa-vesisuspensiosta mitatun pH:n kanssa selitti yli 80 % efektiivisen kationinvaihtokapasiteetin vaihte- lusta. Koko maa-aineistolle voitiin käyttää samaa regres- sioyhtälöä, joka KCI-menetelmällä määritetylle efek- tiiviselle kationinvaihtokapasiteetille oli seuraava: KVK(mvalZkg) = 309 56.8pH(H2 0) + o.oBsCa(mg/l). Vain 16 % näytteistä oli sellaisia, että regressioyhtälöstä laskettu KVK:n arvo poikkesi määritetystä arvosta enem- män kuin 15 °/o. 7