EVALUATION OF SOME CHEMICAL EXTRACTANTS FOR DETERMINATION OF EXCHANGEABLE AMMONIUM IN TROPICAL RICE SOILS

Seven rice soils varying in texture, pH, organic matter and total nitrogen content were extracted with 1N and 2N KC1, 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 KC1 or Nacl had no significant effect on the amount of NH+ 4 -N extracted but KC1 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 NH+4 than Morgan's reagent. Overall, KC1 appeared to be better than Nacl; Nacl at pH 2.5 N CH3CooNa and Morgan's reagent were either equally effective or better for some of the soils a! compared to KC1. 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: KC1 > NaCl pH 2.5 > NaCl > CH3CooNa, pH 3.0 > Morgan's reagent. © 1979, Taylor & Francis Group, LLC. All rights reserved.