Simulation And Multidimensional Critical Regulation Of Water And Nutrient Transport In Agricultural Fields

Our country is an agricultural country with a large shortage of water resources. The traditional mode of agricultural production is high consumed and inefficient, which not only causes a waste of water and fertilizer resources, but also leads to water pollution worsening. Therefore, quantitative study of the nitrogen transformation and transport process in the changing irrigation and drainage mode and optimizing the irrigation and drainage critical control mode which is suitable for China’s southern rice irrigation district have a certain theoretical and practical value for promoting the agricultural production and efficiency, improving the water and fertilizer use efficiency, reducing the loss of water and fertilizer, preventing and controling the non-point source pollution and building water-saving and pollution controling healthy and ecological irrigation district. By reviewing the theories of water-saving irrigation, controlled drainage, water and fertilizer coupling and critical control, on the basis of field experiments and model simulations, this paper systemly analyzed the nitrogen migration rule and water and nitrogen use efficiency under the condition integrated water-saving irrigation and controlled drainage, and built up paddy water and fertilizer critical control system. The main results are as follows:1. Based on the experiment of irrigation and drainage control of paddy field’s non-point source pollution conducted in Tuanlin Experiment Station in2007-2008, the migration and transformation rule of paddy field’s under different water-saving irrigation method, nitrogen fertilization and drainage conditions was comparatively analyzed. Results showed that under the different irrigation treatment, and the concentration of NH4+-N and TN in soil water of the light irrigation and deep storage management was higher than that of the shallow ground irrigation, while the concentration of NH4+-N in soil water was on the contrary; compared with the traditional drainage, controlled drainage treatment increased the concentration of nitrogen in soil water and the content of NH4+-N in soil, which decreased the water loss of NO3--N、NH4+-N、TN by34.08%、7.11%and11.31%, respectively.2. Based on the in-situ data, the water and fertilizer utilization efficiency of rice was analyzed, results showed that increasing nitrogen was beneficial for improving the nitrogen content of rice and its organs, but the excessive nitrogen not only went against the transfer of nutrients to the panicle, but also decreased the utilization efficiency of nitrogen; Compared with the shallow ground irrigation, shallow deep storage irrigation decreased the irrigation quantity and drainage quantity by up to29.7%and34.5%respectively, and the utilization rate of rain was higher. Compared with the traditional drainage, controlled drainage raised the groundwater level and reduced the drainage quantity by7.59-9.71%, promoted the accumulation of nitrogen in rice stems and leaves, and under the condition of low nitrogen utilization, significantly improved the rice production and promoted the grains’nitrogen accumulation which increased the utilization ratio of nitrogen; giving consideration to the synergistic effect of irrigation, nitrogen and drainage, the integrated mode of shallow deep storage irrigation, medium nitrogen utilization (135kgN/hm2) and controlled drainage (50cm) was a better treatment mode, the gross inflow water productivity was1.031kg/m3, and the yield effect of nitrogen was28.29kg/kg.3. Based on the in-situ data, the water and nitrogen coupling effect of yield model in the whole growth period under the condition of water-saving irrigation and controlled drainage was built up, the formula was Y=-0.029x1/2-0.065x2/2+0.005x1x2+42x1+19x2-8525. According to the analysis, the gross inflow water productivity was739.15mm, the quantity of nitrogen utilization was174.58kg/hm2, the maximum yield was8656.5kg/hm2, the gross inflow water use efficiency was1.17kg/m3, the nitrogen agronomic efficiency was49.58kg/kg.4. The in-situ date was used for model validation, results showed that the DNDC model did good to the quantitative simulation of the rice yield, nitrogen adsorption and the dynamic handle rule of the nitrogen in the paddy field’s soil surface, and the correlation coefficient was up to0.8; under the condition of water saving irrigation and controlled drainage, the paddy field soil nitrogen pool in2008showed to loss, the amount of loss was54.7～127.6kg/hm2and gradually decreased with the increasing quantity of nitrogen utilization, when the nitrogen utilization was the same, there was a little difference between shallow deep storage irrigation and shallow ground irrigation, when the nitrogen utilization was handled, the irrigation and drainage mode of controlled drainage+shallow deep storage irrigation had less nitrogen deficit; the sensitivity analysis suggested that nitrogen utilization was the key factor influencing the rice yield and the mercury exchange of nitrogen; rainfall and irrigation greatly affected the leaching and runoff lose nitrogen, and slightly affected the rice yield and the absorption of nitrogen which had a negative effect on ammonia-volatilizing; increasing the depth drainage would decrease the leaching and runoff loss of nitrogen, but showed negative influence on the rice yield, the absorption of nitrogen and runoff loss. 5. The water and fertilizer critical adjustment model was built up, and though combining DNDC model, the paddy field’s non-point source pollution irrigation and drainage critical adjustment control model was put forward, which was the condition of alternate wet dry irrigation, nitrogen utilization of170.3kg/hm2and the controlled drainage deep of20cm. Compared with the normal condition (continuous flood irrigation, nitrogen utilization of262kgN/hm2, and free drainage), the nitrogen utilization was save by35.0%, the average yearly irrigation and drainage were reduced by31.4%and23.7%respectively, water use efficiency and nitrogen agronomic efficiency were improved by up to13.4%and39.5%respectively, the proportion of nitrogen absorption was improved by approximately11.4%, the proportion of water loss and ammonia volatilization were reduced by approximately17.12%and7.17%respectively.