Response Of Sunflower Growth And Water-nitrogen Transport To Different Nitrogen Fertilizers Under Subsurface Drainage And Field Drainage Simulation

In order to solve the problem of salt drainage accompanied by nutrient loss under the condition of subsurface drainage,the pollution reduction regulation mechanism suitable for subsurface drainage farmland in saline irrigation area was explored.In this thesis,the typical subsurface drainage test field in Hetao Irrigation District of Inner Mongolia is selected as the research area,and a two-year subsurface drainage monitoring test is carried out.Three treatments,common urea（CK）,controlled release fertilizer（CF）and organic silicon water soluble slow release fertilizer（OF）,were set up to study the response of water and nitrogen migration and crop growth to different nitrogen fertilizers under the condition of subsurface drainage in saline farmland under the same irrigation amount and pure nitrogen application rate.The change rules of crop response,farmland water and soil environment impact and nitrogen assimilation behavior under subsurface drainage farmland water-nitrogen regulation mode were clarified.Combined with source regulation,the DRAINMOD model was used to simulate the water,salt and crop yield in the process of subsurface drainage,and the technical parameters of subsurface drainage engineering suitable for subsurface drainage and salt drainage and reducing nutrient loss and pollution discharge were optimized,which provided a theoretical basis for the treatment of saline-alkali land by subsurface drainage in Hetao irrigation area.The main conclusions are as follows:（1）Through the analysis of spatial and temporal variation and spatial structure of soil water and salt under the condition of subsurface drainage,it was obtained that the water content and salt content in 0–160 cm soil layer had strong spatial correlation and showed moderate variation level.The soil salinity at different horizontal distances from the pipe was significantly different.With the increase of horizontal distance,the soil desalination rate decreased.The soil desalination rates at 11 m and 0 m were 10.38%and 21.15%,respectively.The buried depth of subsurface pipe has significant influence on the changes of soil moisture content and salt content.After irrigation,the soil moisture content and salt content were 1.7 m<1.5 m<1.2 m.The average desalination rate of soil decreases with the increase of the buried depth of the pipe,that is,when the buried depth of the pipe is 1.2 m,the overall desalination effect of the soil is the most obvious.（2）Under the same amount of pure nitrogen,controlled-release fertilizer and silicone water-soluble controlled-release fertilizer were conducive to promoting the growth of sunflower.Among them,controlled-release fertilizer can achieve nitrogen fertilizer backward by controlling the release rate of nutrients.One-time basal application of controlled-release fertilizer is conducive to the continuous and effective supply of nitrogen in 0–40 cm soil layer,which is 1.80 times and 1.24 times of that of ordinary urea and organic silicon water-soluble slow-release fertilizer,respectively.At the same time,it can improve the effective utilization rate of light energy at the late growth stage,which is about1.13 times and 1.06 times of that of the two,which is conducive to the accumulation of organic matter.Compared with common urea and organosilicon water-soluble slow-release fertilizer,the nitrogen accumulation in grains under controlled-release fertilizer treatment increased by 57.66%and 23.25%,and the nitrogen uptake in plants increased by 63.08%and 11.4%,respectively.The average yield increased by 40.54%and 14.07%,respectively.At the same time,it can also improve the partial productivity of nitrogen fertilizer and harvest index of crops,and promote the absorption and utilization of nutrients by crops.（3）There was high NO₃^--N residue in 0-160 cm soil layer under different fertilization treatments after sunflower harvest,and the proportion of NO₃^--N residue in 80–160 cm soil layer reached more than 60%of the total residue.Compared with ordinary urea and organosilicon water-soluble slow-release fertilizer,the application of slow-release fertilizer can reduce the residual accumulation of NO₃^--N by 14.92%and 7.78%in soil.Reduced48.37%,33.81%of nitrogen deep leaching.In the subsurface pipe effluent,the concentration of NO₃^--N was about 5–8 times that of NH₄⁺-N.The NO₃^--N loss under the treatment of common urea and organosilicon water-soluble slow-release fertilizer was 1.50and 1.25 times that of the slow-release fertilizer,and the NH₄⁺-N loss was 1.95 and 1.22times that of the slow-release fertilizer,respectively.The application of controlled release fertilizer under subsurface drainage could reduce nitrogen leaching and nitrogen loss in soil.（4）Calibration and verification of groundwater depth and soil salinity data by DRAINMOD model.The results show that the model simulation accuracy is high,and it can better simulate the water and salt conditions under concealed pipe laying conditions in the region.Therefore,this model is used to further optimize the buried parameters of subsurface drainage system.It is concluded that when the buried depth of concealed pipe is1.5 m and the spacing is 20 m,not only the groundwater level can be effectively reduced,but also the high yield can be obtained.The effect of salt discharge is the best,which is the suitable layout parameter of concealed pipe in the study area.Combined with crop growth,nitrogen distribution and loss,concealed pipe layout parameters,the effect of applying controlled release fertilizer on stable yield and efficiency and reducing environmental pollution risk was the best when the concealed pipe depth was1.5 m and the spacing was 20 m.It was the suitable regulation mechanism under the condition of moderate salinization soil subsurface drainage.