Migration And Transformation Of Urea In The Soil Under The Conditions Of Irrigation And Fertilization

Drought stress and the supply of water fertilization is not harmonious, severely restricts the agricultural production development of drought region in our country. And in recent years, for the sake of high yield while blind fertilization, unreasonable method of fertilization is not only causing a waste of fertilizer, and has brought a certain degree of pollution to the environment. Therefore, the application of fertilizer in irrigation and fertilization is not only to ensure food production, while still water-saving irrigation to improve urea utilization and reduce environmental pollution caused. But if encounter rainfall after irrigation and fertilization, heavy rainfall will cause the loss of surface layer of soil nitrogen, soil nitrogen deep inside the leaching, these will cause different degrees of pollution to surface water and ground water. So study and formulate a reasonable irrigation and fertilization measures on application agricultural development of agriculture has important theoretical significance.This paper combines the indoor tests and theoretical points, and use one-dimensional vertical soil column to simulate ground irrigation urea solution in indoor test. Analyzes the impact of different soil density (1.3g/cm3,1.4g/cm3,1.5g/cm3), different urea concentration (300mgN/L,500mgN/L,700mgN/L, and900mgN/L), different Rehydration water (0.3L,0.6L,0.9L,1.2L) and different Rehydration time (1d,3d,5d,7d,10d) and different Irrigation strategy on the migration and transformation of urea in soil. The resulting findings are as follows:(1)In the initial stage of water infiltration rate is larger, with the extension of time, the infiltration rate decrease gradually to reach a steady infiltration. Cumulative infiltration amount, wetting front advance distance increased with the prolongation of the infiltration time. Under the condition of different soil bulk density, the same infiltration lasted, the greater the density of infiltration rate is small, the accumulation infiltration quantity is little, the moist front promote more short distance. Under different urea infiltration concentrations, accumulated, infiltration rate of moist, wetting front advance distance all increased along with the urea liquid fertilizer increased. Under different fertilization strategies, the infiltration rate, cumulative infiltration, wetting front advancing distance has little effect, and is basically the same lasted; the first irrigation of liquid fertilizer soil column, soil water infiltration rate greater cumulative infiltration, wetting front advancing distance is larger.(2)under different soil density, different urea liquid concentration condition, the water infiltration rate, accumulated, infiltration amount and wet front process and the infiltration time all can use the relationship between power function fitting, and the correlation coefficient are above0.9.(3)Top soil moisture content is bigger, the bottom’s is smaller. Under the condition of different density, in the same deep, Moisture increases with the increase of soil bulk density, but wet area near the front (70cm below) is reduce with the greater of the soil bulk density. Urea liquid concentration on the distribution of soil moisture contents basically no influence, but significant effect on water content. Under Different complex water, the soil moisture content increases, wet front expanded. After water amount is larger, the greater the moisture content and moisture scope is bigger also. Under the same after water conditions, after irrigation rehydration the longer the time interval, the greater the scope of soil moisture, the bigger the soil moisture distribution more evenly. The shorter the time interval after water, the smaller change of soil moisture. Fertilization strategies on soil moisture content and distribution of the impact is not big,0-45cm within the scope of the soil layer, the same soil depth place,1/2W+1/2N the moisture content of scheme is greater than1/2N+1/2W scheme of the moisture content, and45cm below the opposite.(4)Distribution rules of ammonium nitrogen is first increases and then decreases in the soil column profile, in the soil depth15cm place ammonium nitrogen concentration is the largest, The larger soil density, the greater the surface soil ammonium nitrogen, the smaller the range of the distribution of ammonium nitrogen; the shorter the distance nitrate transport. Urea fertilizer solution concentration has little influence on the distribution of soil ammonium and nitrate nitrogen in the profile, but it produce a greater impact on its content, the conversion of the generated soil ammonium, nitrate content and soil nitrate distribution range all increase along with the irrigation fertilizer solution concentration increases.(5) Under different rehydration water conditions:the distribution of ammonium nitrogen in the soil profile is first increased and then decreased, the greater rehydration water, the larger the distribution of ammonium nitrogen, the greater concentration of nitrate nitrogen at the wetting front, nitrate nitrogen distribution range is the greater, the more easily cause the loss of nitrate leaching. Different rehydration time:take rehydration time in this test within the interval, ammonium conversion finished the required time of14days; the longer the rehydration time interval, the more evenly distributed of ammonium nitrogen, the smaller influence to distribution discipline of ammonium nitrogen, the lower the content of ammonium nitrogen in the soil profile. The longer time interval, the higher the concentration of nitrate, nitrate leaching is more obvious.(6)ammonium nitrogen accumulate in the0-25cm soil within in1/2W+1/2N program; for the1/2N+1/2W program, ammonium nitrogen content along the vertical direction first increases and then decreases, and higher concentration in soil35～45cm within the region;1/4W+1/2N+1/2W plan in the content of nitrogen ammonium along the vertical direction to increase gradually, then decreases, and soil layer25-35cm within the scope of the content is bigger; For the1/4N+1/2W+1/4N scheme, the distribution regularity of ammonium nitrogen is first reduce and then increase and reduce again in the profile, the soil surface ammonium nitrogen content is bigge,45to55cm soil area also have concentration peak appearing. Four irrigation fertilization strategies, nitrate content are all lower than the background value in wet area internal. Nitrate concentration accumulated at the wet front edge.