Water And Nitrogen Dynamic Simulation Research In Farmland Vadose Zone

The current situation of water environment are destroyed seriously in China, shortage of water resources, groundwater nitrogen pollution in the worsening of ecological environment problem increasingly prominent, and agricultural non-point source pollution will add to environmental pollution. Therefore, the research of water and nitrogen in the farmland ecosystem dynamics and its balance of payments situation for the scientific management of farmland water and nitrogen, ease of nitrogen pollution provide beneficial basis, to improve the agricultural productivity, improve the ecological environment quality has a long-term significance.Within this study chooses farmland in Jinghui Irrigation Distrie as the study area, medium in vadose zone as the research object, migration of water and nitrogen as the main line, combining with field experiment and laboratory analysis as the basis, to make theoretical analysis and simulation study, analyze migration regularity of water and nitrogen in the vadose zone, and illustrate water and nitrogen balance of payments according to the model formulated to provide a scientific basis for pollution control and sustainable development of regional agriculture. The main results were as follows:(1) Irrigation water is 37 m3 and 53.3 m3 respectively in 2013 and 2014 of summer maize trial period, the moisture migration maximum depth is 500 cm. Irrigation water is 40 m3 and 8 m3 respectively in 2013 and 2015 of winter wheat trial period, the moisture migration maximum depth is 500 cm, 150 cm respectively. Irrigation water is different, different soil layer in response to different soil moisture content, in the four trial period, shallow soil moisture content increased after irrigation, and the bigger the irrigation water,the greater the amount of increase. Irrigation water is 37 m3, 40 m3 of deep soil moisture response efforts and time are better than irrigation water is 53.3 m3, 8 m3, indicated that irrigation water is too large or too small are not conducive to the increase of soil moisture. In the experimental period, due to the irrigation makes the shallow soil moisture movement is intense, lead to migration of nitrate nitrogen which not adsorbed on soil colloidal particle, Cause nitrate peak move down, A large number of irrigation make nitrate nitrogen migration distance is farther,tends to accumulate in the bottom of the layers. The irrigation and fertilization at the same time, prone to NO3一- N leakage phenomenon in the bottom of the soil layers. It indicates that after nitrogen fertilizer into the soil, nitrogen not all absorbed by the soil utilization, Part of nitrogen move with irrigation water to the bottom to occur leakage.(2) The evapotranspiration which affected by climate condition, crop root and leaf area index of summer corn trial period is greater than the winter wheat trial period.In two summer corn trial, evaporation accounted for 5.88% and 3.92% of the total water inflow respectively, crop transpiration accounted for 26.88% and 14.85% of the total water inflow respectively. Because the root growth situation and climate conditions are similar, the evaporation is similar, but the root water absorption is influenced by a lot of irrigation water, indicate that a large number of irrigation adverse to crop uptake water. In the two winter wheat experiments, 2015 winter wheat root growth and leaf area flourish than in 2013, make 11.43 mm of 2015 winter wheat crop transpiration is greater than 3.65 mm of winter wheat in 2013.The evapotranspiration of the trial period of winter wheat in 2013 accounted for 3.52% of the total surface flow.The evapotranspiration accounts for 12% of the total loss of 2015 winter wheat trial period, accounted for 46.63% of the total surface flow.And leakage at the bottom of 88% of total loss which comes from 73% of soil water storage, Thereby causing loss to the water in the system, a small amount of irrigation water can not contribute to the retention of water in the system.Water retention volume accounted for 52.99% and 57.05% of the total inflow water when the irrigation water is 37 m3 and 40 m3 respectively. The leakage at the bottom of soil layer accounted for 49.26% of the total inflow water when the irrigation water is 53.3 m3 of corn summer trial period in 2014,and moisture retention volume accounted for 31.97% of the total water,a large number of irrigation wate is not conducive to maintain moisture in the soil system. Runoff losses occur in irrigation on the same day of winter wheat trial in 2013, loss of 44.57 mm, accounting for 21.06% of the total inflow. This is because the winter surface soil permeability coefficient little make water penetration ability is weak, alarge amount of irrigation water fails to timely infiltration leads to ponding water occur on the soil surface. And when the water layer over a given 5 cm, the irrigation water will overflow test area outside of the resulting runoff losses.(3) Fertilization can cause soil ammonium nitrogen flux changes inside the soil system, and effect smaller on nitrate nitrogen flux changes. Soil internal ammonium nitrogen flux change 81.16% and 61.84% cause by fertilization respectively in two fertilization experiment. Mineralization is the largest supplies of soil ammonium nitrogen in the system, most ammonium nitrogen form from mineralization act on nitrification process.Nitrogen fertilizer will aggravate nitrification so that nitrification ratio increases, the net neralized flux is the largest at the simultaneous fertilization and irrigation of 2013 summer corn and 2015 winter wheat trial period, were 552.2 mg/cm2 and 446.8 mg/cm2 respectively. And the biggest irrigation of corn period in the summer of 2014,its net neralized flux is the smallest were 282.2 mg/cm2, excessive irrigation make nitrification restrained, lead to the formation of anaerobic conditions can promote the denitrification.(4) The bigger of root water uptake,theits bigge its nitrogen uptake,Fertilizing amount bigger make root absorption of nitrogen accumulation amount increases, compared with ammonium nitrogen, nitrate nitrogen is more easy to be absorbed by roots. Ammonium nitrogen and nitrate leaching cumulative fluxes at the bottom of the largest when the water leakage was the worst of 2015 winter wheat period, accounted for 0.66% and 19.01% of total nitrate nitrogen expenditure flux, respectively. Pearson correlation coefficient of the accumulate water leakage with ammonium nitrogen, nitrate nitrogen leaching cumulative flux at the bottom is 0.99 in four trials. The loss flux of nitrate nitrogen by surface runoff is 19.9 mg/cm2 accounts for 4.92% of the current total nitrate nitrogen expenditure flux in 2013 winter wheat trial period.