Evaluation of some chemical extractants for determination of exchangeable ammonium in tropical rice soils

Abstract

Seven rice soils varying in texture, pH, organic matter and total nitrogen content were extracted with 1N and 2N KCl, 1N and 2N Nacl, 10% Nacl at pH 2.5, N CH₃ CooNa at pH 3.0, and Morgan's reagent using a soil: solution ratio of 1:10. The ammonium in the extracts was determined by steam distillation with MgO.

The normality of KCl or Nacl had no significant effect on the amount of NH₄ ⁺ ‐N extracted but KCl proved a better extractant than Nacl. However, Nacl at pH 2.5 generally extracted significantly higher amounts of NH₄ ⁺ ‐N as compared to the neutral salt solution. N CH₃ CooNa at pH 3.0 did not extract more NH₄ ⁺ than Morgan's reagent. Overall, KCl appeared to be better than Nacl; Nacl at pH 2.5 N CH₃ CooNa and Morgan's reagent were either equally effective or better for some of the soils as compared to KCl. However, when recovery of the known amount of NH₄ ⁺‐N applied to soils was used as a criterion, the efficiency of these chemicals were in the following descending order: KCl > NaCl, pH 2.5 > NaCl > CH₃CooNa, pH 3.0 > Morgan's reagent.