Simulation Studies On Nitrogen Dynamics And Fertilizer-N Optimization For Rice Production

Simulation studies on crop growth and development began in 1960's with the application in crop physiological ecology of system analysis methodology and computer technology. Crop simulation is referred to set up computer model to analyze quantitatively the ecophysiological processes including crop growth and development, photosynthesis, yield formation, etc., and the effects of environmental factors, management measures, by applying the methods of system analysis and integrating the related disciplines, such as plant physiological ecology, agronomy, meteorology and soil science.Outstanding achievements have been made for crop simulation studies in past 40 years, but it still needs more efforts to perfect the simulation models. Rice model is an important research field, especially for simulation of rice growth limited by nitrogen. Based on related literatures and field experiments, a simulation model for nitrogen dynamics and fertilizer-N optimization in rice was set up, and the corresponding software was also developed to simplify model's application. The software running for Windows98 or above was programmed with Visual Basic 6.0. Innovated progress in present study includes the following aspects. (1) By combining related theory and technology of crop growth simulation, two models were ret up to simulate nitrogen dynamics and fertilizer-N management in rice growth and production, which can be used to study growth, development, nitrogen dynamics and optimizing plans for fertilizer-N application. (2) Price's numerical optimization algorithm was integrated in rice nitrogen model to realize the computation of some fertilizing parameters and improve the model's ability in production. (3) Programmed with Visual Basic 6.0, simulation software for above models was developed. The software is designed on the basis of windows interface, so it is easy to operate and can meet common users' applying demand.1. Effects of fertilizer-N application levels on rice productionField experiments were carried out to study the effects of fertilizer-N application levels on rice production in Hangzhou city in 2001 and 2003. There were six treatments with nitrogen application of 0, 75, 150, 225, 300, 375 kghm"2. Three varieties of Wujin-9728, Bing-9363 and Bing-9652 were used as materials.The results showed that the fertilizer-N application levels obviously affected on leaf area index (LAI), biomass, yield formation and nitrogen content of crop. LAI, dry matter of leaves, stems and roots increased with the rise of fertilizer-N continuously, and the effects were more distinctly at low or medium levels of fertilizer-N. There existed a linear relationship between nitrogen content of plant organs and fertilizer-N input. For yield components, panicles increased with the rise of fertilizer-N all along, while number of grain per panicle, fertility rate and 1000-grain weight had different response to low or high fertilizer-N, though a decreasing tendency could be found as a whole. The effects of fertilizer-N on yield could be expressed by quadratic parabola. Fertilizer-N application of 140-200 kghm"2 was considered suitable for present local conditions, according to the parabola and the principles of marginal benefits of economics. By integrating related factors, it is feasible to cut 30% of fertilizer-N from current application levels.2. Simulation of rice nitrogen dynamicsRNDSM, a simulation model for nitrogen dynamics in rice crop, was built to study rice production under conditions limited by nitrogen, based on previous models. The model is made up of basic processes including phenological development, leaf area development, photosynthesis, expiration, dry matter partitioning, yield format;on, etc., and nitrogen related processes, such as the demand, supply, uptake, partitioning, transfer of plant nitrogen.RNDSM was validated by the field experimental data. From the results of validation, the model could simulate the phenological development accurately, only one or two days' differences between the simulated and observed growth du...