| A mathematical model (RICENIT) was developed to simulate nitrogen transformations in rice field. The processes simulated in the model included decomposition, nitrification, denitrification, volatilization, N loss with transpiration from leaf, N uptake by rice, biological N fixation, N diffusion, N leaching and N runoff, and ammonium fixation by clay and organic matter. Selected published field studies were simulated using this model to validate RICENIT by comparing the predicted and observed nitrogen utilization by rice, nitrogen status in soil and water, and N losses from the rice field. An evaluation of the results showed that the model performed satisfactorily. A sensitivity analysis of six factors in the model identified the important factors affecting total N loss to be soil and water pH, fertilizer N rate and temperature. The result of the simulations suggested that denitrification following nitrification and ammonia volatilization were the major sources of N loss in rice field. The predicted N loss with transpiration was found to be proportional to rice canopy size and N application rate.;Greenhouse experiments with ;In the reproductive stage, the combined contribution of soil biomass, algae, leaf tissue to rice N uptake was 27 percent of total fertilizer N taken up by rice during this period. Although native soil-N supplied rice with 9.5 g N m... |
