Evaluation of some chemical indexes for predicting mineralizable nitrogen in tropical rice soils

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Abstract
Five chemical indexes were evaluated for predicting mineralizable nitrogen in 39 rice soils from the Philippines having a wide range in texture, pH and organic matter. The indexes evaluated were based on oxidative release of soil ammonium‐N by alkaline permanganate, acid permanganate, acid dichromate, hydrogen peroxide and dilute sulfuric acid. The amounts of mineralizable N obtained by the chemical indexes were correlated to varying degrees with those determined by anaerobic incubation methods. The basis of good agreement for mineralizable N determined by chemical arid biological indexes appears to be due to the fact that both derive the mineral N from the pool of organic nitrogen in soils. The support for this conclusion was obtained by highly significant correlations between mineralizable N determined by chemical and biological indexes with soil organic C and total N contents of soils. These results alongwith other evidence suggest that the chemical indexes may be useful for predicting pools of mineralizable N in wetland rice soils.