Nitrogen Dynamic Simulation And Management In Rice

Nitrogen dynamic simulation models in rice were developed through the field experiments and data collection. The simulation models included submodels of mineralization of soil organic nitrogen, nitrogen release from straw decomposition, nitrogen uptake by rice plants and nitrogen partitioning among the organs of rice plants.The effects of temperature and soil moisture on the decomposition of straw were described by exponential functions and segmented linear functions respectively and their synthesized effects were described by "normalized days" in the sub-model of soil nitrogen dynamics. The concept of "whole swallowing" modeling structure was developed in the new modeling structure, in which, the forms and compositions of the organic materials changed with the process of decomposition and as a result nitrogen contents in the straw residue were changed. The amount of released nitrogen was estimated by the difference in nitrogen contents between the initial organic material and the residue. Because of its low parameter requirement and ease of parameter estimation through simple experiments, the developed simulation was more practical than de Vries's "pie-eating" modeling structure.The relative satisfying degree of soil nitrogen supply, which was defined as the ratio of soil mineral nitrogen concentration to the critical nitrogen concentrations was used to calculate nitrogen uptake by rice plants. The critical nitrogen concentrations in soils varied with physiological development time (PDT) and corrected with the relative nitrogen uptake rates with PDT under high yielding conditions. Nitrogen. Partitioning indexes of the leaf, sheath, stem and panicle were simulated according to the data from the experiment in 2002 and 2003.The methods of pre-sowing decision making and dynamic adjustment during growing period of nitrogen fertilization were put forward based on the rice growth simulation models. The pre-sowing fertilization decision was made through thecomprehensive evaluation of criteria such as rice grain yield, nitrogen fertilizer efficiencies, nitrate leaching amount and soil organic matter balance computed by the simulation models under the normal climate conditions for various fertilization plans. The time of dynamic nitrogen adjustment were determined by regular patterns or by the comprehensive evaluation of soil mineral nitrogen concentration and rice population status.