The relation of potentially mineralizable soil nitrogen, No, to the oxidative release of NH4-N from soil organic matter during extraction with acid KMnO4 was investigated, using 62 soils. Included in the study were members of 8 soil orders comprising 43 noncalcareous and 19 calcareous soils. Soils were extracted with 1 N H2SO4 solutions of 0.05 and 0.1 N KMnO4 (HOx) and with 1 N H2SO4 (H) alone for 1 h at room temperature, and amounts of NH4-N released were determined. The expression HOx - H denotes the quantity of NH4-N released owing to partial oxidation of soil organic matter. Later, a more direct and simpler procedure for determining oxidative NH4-N release was adopted, in which soils were preextracted with 1 N acid, and the soil residues were extracted with acidic KMnO4.
Regression equations that may be useful in predicting No from the oxidative release of NH4-N were developed. Amounts of NH4-N released by oxidation with 1 N H2SO4 solutions of 0.05 and 0.1 N KMnO4, respectively, were approximately one-third and one-half of No. We conclude that the NH4-N was derived from oxidation of the soil organic N fraction most readily susceptible to biological mineralization.