Simulating Net Primary Production Of Agricultureal Vegetation--Rice And Wheat

On the basis of the principles of plant physiology, agro-meteorology and soil environment, net primary production of rice and wheat crops was modeled. The model includes two main functional modules: photosynthesis and respiration, and nitrogen transport within soil-plant system. The processes of photosynthesis and respiration are driven by environmental variables and plant nitrogen content. The transportation of nitrogen within soil-plant system is determined by simulating the processes of crop nitrogen uptake, soil nitrogen mineralization and synthetic nitrogen release.In the photosynthesis sub-model, the simulation of radiation, temperature, water, and CO2 were general. The work emphasized the leaf maximal photosynthetic rate, according as crop nitrogen content. The model enhanced consequently the mechanism, avoiding fixing value.In the respiration sub-model, the simulation of growth respiration and maintenance respiration was conventional. In the research, we discovered maintenance respiration coefficient was correlated with crop nitrogen content. For rice, the expression was Rm=0.0085 N 96 (i)2-0.0049 N % (i) (r2=0.9776), and Rm=0.0124 N % (i)-0.0076 (r2=0.9879) for wheat. In the past work, maintenance respiration coefficient was fixed 0.01and 0.02((C)/g-g-1) for pre-heading and after heading. So, the work enhanced the model mechanism and science, simulating maintenance respiration coefficient by crop growth.In the transportation of nitrogen within soil-plant system sub-model, whether simulation the crop nitrogen content was exact is pivotal, because crop nitrogen content was key in photosynthesis sub-model and respiration sub-model. And the crop nitrogen dynamic was directly affected by soil nitrogen supply. In the work, we simulated nitrogen supply by the soil and fertilizer by field experimentation, and simulated rationally the progress of soil supply dynamic in the field. Before, the soil nitrogen simulation was in the laboratory by simulating one or more soils mineralization, and run short of effective validation. By validating the soil nitrogen supply in the different region of our country, the soil nitrogen sub-model not only simulated well and truly, but also was applied in broaderarea. So the rationality of net primary production of agricultural vegetation model was enhanced, and the model reflecting practice ability was strengthened.At the same time, this model developed by the authors was validated against a total of 98 independent data sets to simulate net primary production (NPP) of agricultural vegetation. These data sets come from literature review and include field measurements conducted in different regions of China with various rates of N application. Other was rice and wheat net primary production in Jiangsu Province from 50's to 90's to validate the model. Model validation indicates that NPP of rice and wheat crops in main cultivated-area of China can be well simulated from weather, soil and N fertilization. A comparison between the simulated (T) and the observed NPP (X) resulted in a regression of 7=1.05X-16.8 (r2=0.771, P<0.001, n=98). And model could integrate the weather, soil and field management.According as prediction of atmospheric CO2 concentration and temperature by Intergovernmental Panel on Climate Change, the validated model scenario prediction for Nanjing area suggests that the increase of atmospheric CO2 concentration will reduce carbon fixation by rice and wheat crops, but the effect of Global warming to wheat carbon fixation is less than to rice carbon fixation. Under present and future scenario with atmospheric CO2 concentration of 540 mol-mor' and temperature increment of 1~4 C, N fertilization will enhance carbon fixation of rice and wheat crops. The enhancement for wheat is more significant than that for rice crop. However, the application of N will not significantly improve the carbon fixation; even reduce rice NPP when the N application rate is higher than 150kg-hm-2.