Immobilization, mineralization and the availability of the fertilizer nitrogen during the decomposition of the organic matters applied to the soil

Immobilization and mineralization of the tracer nitrogen (K15NO3) applied to the soil together with several organic matters during their decomposition was investigated in incubation experiments. After incubation for three months at 30°C, the decomposition rates of rice straw, hardwood bark, sawdust, softwood bark and peat moss were 41, 15, 7, 5, and 5%, respectively. After incubation for three months at 30°C, 100 and 80% of the fertilizer nitrogen were immobilized in the treatment with 2.0% of rice straw and sawdust carbon, respectively. These resulted in the lowered uptake of the fertilizer nitrogen by plants. In case of peat moss and barks, the amount of fertilizer nitrogen which transformed to the organic nitrogen fractions was quite small and the plant uptake of the nitrogen was hardly affected. Remineralization of the immobilized nitrogen was clearly observed after 2 months' incubation in case where rice straw carbon was added to the extent of 0.5 and 1.0%, but it was not observed in case where other organic matter carbon was added. The data showed that peat moss and barks were highly resistant to the action of microorganisms. As a results the immobilization process of the fertilizer nitrogen incubated with these organic matter was quite slow.