SOIL EXCHANGEABLE CATIONS AND ALUMINUM MEASURED BY AMMONIUM-CHLORIDE, POTASSIUM-CHLORIDE, AND AMMONIUM ACETATE

Cation exchange capacity (CEC) and A1 saturation are often determined by extraction of the bases with 1 M NH4OAc, pH 7, and the A1 with 1 M KC1. This method was compared to 1 M NH4Cl to extract both bases and Al. The latter method has the advantages of measuring CEC at the soil pH and one-step extraction. Data sets included three field samplings from 4 locations (7 soil types) and samples from a greenhouse experiment with 8 soils (total N=248). Differences between individual pairs of data were evaluated using T-tests. Most soils were acid and CEC was predominated by Al and Ca. The two methods compared favorably for Al with slightly more Al being extracted by NH4Cl than by KC1. Significantly less Ca was extracted by NH4Cl than NH4OAc. Coefficients of determination were high (> 0.98) for Ca, but the regression slope was less than one (0.85). The methods compared well for extractable Mg, K, and Na, but those were minor constituents of the CEC. CEC and Al saturation differences followed those of Ca. The NH4Cl method is recommended for samples that have not been recently limed, but not for samples containing residual lime. © 1990, Taylor & Francis Group, LLC. All rights reserved.