CATION EXTRACTION CAPACITY OF AMMONIUM ACETATE, SODIUM ACETATE AND AMMONIUM CHLORIDE

The cation exchange capacity (CEC) of soils is important for soil fertility evaluation. Extracting cations from the exchange complex with ammonium acetate IN, pH 7 (AA) is the routine. The AA method induces errors in the determination of the CEC. Thus, extracting cations with AA was compared against the results obtained with ammonium chloride 0.2N (CA) and sodium acetate IN, pH 8.2 (AS). Soil samples from nine counties of Lara state, Venezuela, were used. The CEC was obtained for each method by the sum of cations. Results were normalized for comparison among them. The results showed that the soil pH was in the 3.3-8.3 range. The highest CEC values were obtained with AA, which agrees with reports that this method raises the real soil CEC value. The lowest CEC values were obtained with AS. The CA method resulted in CEC values that ranged between those of the other two methods. No statistic association was found between the AC and the AA CEC values, or between the AS and the AC methods. The Mg2+, K+ and Na+ soil extractable content showed a high statistic association between both the AA and the AC methods. However, no statistic association was found between the Ca2+ values from AC and the AA. It is concluded that the lack of association between the CEC determined by the AA and AC methods was due to the soil content of Ca2+, which was extracted in excess by AA.