Nitrogen behavior in tropical wetland rice soils

Laboratory and greenhouse pot experiments show that tropical wetland rice soils are very diverse in the inherent fertility. The mineralization of native soil nitrogen differed among the soils studied. Air-drying and oven-drying of soils resulted in a large increase in nitrogen mineralized. The main source of mineralized N was the amino acid and amino sugar fractions.N uptake by rice was well correlated with N mineralized in incubation of air-dried soil which should reflect accurately the nitrogen-supplying capacities of tropical wetland rice soils during the growing season. However, plant uptake of available soil nitrogen was also correlated with total nitrogen content of soils, and it would appear that total soil nitrogen which is simple to determine is a satisfactory index of the N supplying capacities of tropical wetland rice soils. Exclusion of problem soils like acid sulfate soils improved the correlation.