Difference in N Transformations in Various Types of Soils, and Effect of Applied Organic Materials on N Dynamics

Abstract

Difference in N transformations in 4 types of soils, and effect of applied organic materials on N transformations were investigated in experiments using 15N as a tracer. The rates of nitrification and N immobilization were conspicuously different by the soil types, and the total amount of immobilized N in each soil was predictable by using the rates of nitrification and immobilization determined by the incubation experiments. The organic materials such as dried hog feces and wheat straw enhanced N immobilization by microorganisms, which resulted in depressing N absorption by crops as well as mitigating the risk of nitrate leaching. It was demonstrated quantitatively that combined use of chemical fertilizer and organic materials did not always diminish the amount of nitrate leaching due to comparatively large amount of applied N in comparison with the sole application of chemical fertilizer.