Coupling Effect Of Water And Nitrogen On Controlled Release Fertilizer Application And Optimization Of Irrigation And Fertilization System In Salinized Irrigated Area

Water resource shortage and low utilization rate of water and nitrogen have become the main factors restricting agricultural production in hetao irrigated area.Taking sunflower as the research subject,this thesis carried out experiments on the efficient utilization of water and nitrogen under controlled release fertilizer application conditions in typical salinized farmland in the middle reaches of Hetao irrigated area in 2019 and2020.Traditional fertilizer(Basal application diammonium and topdressing urea)and controlled-release fertilizer were applied at three levels of low nitrogen(135 kg/hm~2),medium nitrogen(225 kg/hm~2)and high nitrogen(315kg/hm~2),and set two irrigation level:controlled irrigation(180mm)and full irrigation(360mm).The mechanism of interaction between water and nitrogen in controlled release fertilizer application on salinized farmland was studied,and the effects of coupling effect of water and nitrogen in controlled release fertilizer application on sunflower growth,yield and water and nitrogen use efficiency were explored.The regression equation of coupling effect of water and nitrogen in controlled release fertilizer application was established,and the combination scheme was optimized.The Dssat-Oilcorp-Sun model was used to simulate the accumulation,distribution and transport of dry matter and nitrogen in sunflower.This is of great significance for solving the efficient utilization of agricultural water and fertilizer in salinized areas and the prevention and control of non-point source pollution.The main conclusions are as follows:(1)Soil moisture content increased with the increase of soil depth,and decreased with the growth process.Salt migration to the surface and accumulation.Irrigation can effectively remove salt,and the desalting rate under full irrigation is 49.19%～112.19%higher than that under controlled irrigation.Nitrate nitrogen transport characteristics were consistent with salt content.Compared with traditional fertilizers,nitrate nitrogen content in controlled release fertilizer increased by 3.64%～15.17%at mature stage.(2)Compared with traditional fertilizer,plant height,stem diameter and SPAD of sunflower increased by 3.03%～24.84%under controlled release fertilizer.Plant height,stem diameter and SPAD were proportional to nitrogen application rate,but when nitrogen application rate was more than 225kg/hm~2,the increase of plant height,stem diameter and SPAD gradually decreased.(3)Compared with traditional fertilizer,controlled release fertilizer could increase sunflower yield by 13.89%and water and nitrogen use efficiency by 13.61%to 46.42%in 2 years.Controlled release fertilizer can reduce N surplus,reduce N apparent loss and improve N use efficiency in soil-crop system.(4)In the controlled release fertilizer application of farmland,irrigation quota,applied amount of n fertilizer and sunflower between economic benefits in line with the binary quadratic regression model,by analyzing the main factors,the economic benefits of sunflower effects as follows:irrigation water>nitrogen application,economic benefits along with the increase of nitrogen application rate showed a trend of decrease after the first increase and gradually increased with the increase of irrigation water.According to the model optimization,the highest economic benefit(21000-22500yuan/hm~2)of water and nitrogen combination scheme is:nitrogen application253.71-276.12 kg/hm~2,irrigation 348-361mm in 2019,nitrogen application236.88-282.6 kg/hm~2,irrigation 346-357mm in 2020.It is recommended to use water and nitrogen as controlled release fertilizer in sunflower farmland in salinized area of hetao.(5)Calibration verifies Dssat-Oilcrop-Sun model,nRMSE is 7.16%to 11.09%,NSE is 0.85 to 0.91.The dry matter and nitrogen accumulation of sunflower showed a slow-fast-slow pattern,and the dry matter and nitrogen accumulation of sunflower also decreased due to senescence.Compared with traditional fertilizers,the dry matter and nitrogen accumulation of controlled release fertilizer increased by 24.58%and 60.54%,and the dry matter and nitrogen accumulation of senescence fertilizer decreased by61.60%and 29.19%.Compared with controlled-release fertilizer treatment,traditional fertilizer treatment increased dry matter translocation,dry matter translocation rate and dry matter contribution rate to grain by 27.33%-38.34%.The nitrogen transshipment volume,nitrogen transshipment rate and nitrogen contribution rate to sunflower seeds were significantly positively correlated with nitrogen application rate.High nitrogen increased the nitrogen transshipment volume,nitrogen transshipment rate and nitrogen contribution rate to sunflower seeds by-8.46%to 399.65%.