This method is semi-quantitative and determines the amount of soil exchangeable K, Ca, Mg, and Na residing on the soil colloid exchange sites by displacement with ammonium acetate solution buffered to pH 7.0. Cations are quantitated by inductively coupled plasma atomic emission spectrometry (ICP-AES). Generally, these cations are associated with the exchange capacity of the soil. The method has detection limits of approximately of 1 ppm or 0.01 meq/100g for each cation. The estimation of cation exchange capacity is reported as the sum of the results for K, Ca, Mg, and Na. The method does not correct for calcium and magnesium extracted as free carbonates or gypsum.
Sample amount requested: 10 g (for one or up to all four elements)
Questions concerning limited sample size can be answered by the UC Davis Analytical Laboratory.
Thomas, G. W. 1982. Exchangeable cations. pp 159-165. In: A.L. Page et al. (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.