Soil-plant nutrition studies on tropical rice

The lowland rice depends comparative1y more on the nitrogen supply by the soil resources than the other upland crops. Usually, the rice plant utilizes much more native soil nitrogen than the applied fertilizer nitrogen(1). Accordingly, the paddy soil fertility is usually regarded as a nitrogen supplying potentiality of the soil in a narrow sense. Many studies(2) on the soil fertility proplems have been focused on the availability and the recovery of this organic nitrogen. Decause the yield of rice are primarily determined by the liberation of this organic nitrogen.