Effects Of Combined Application Of Organic And Inorganic Fertilizers On Physicochemical Properties Of High Saline Soil And Growth Of Sunflower In Hetao Irrigation District

The HID(Hetao Irrigation District)is an important commercial grain and oil production base in China,and it is also a typical area where salinization develops.Excessive salinity severely limits the development of local agricultural economy.In order to increase production,the application of chemical fertilizers is increasing year by year.Long-term unscientific fertilization methods lead to low fertilizer utilization rates and serious threats to the ecological environment.Therefore,the excessive application of chemical fertilizers and soil salinization have become important factors limiting the improvement of crop productivity in the HID.In this study,a field experiment was carried out for two consecutive years from 2019 to 2020 on the high saline soil in the HID.Under the same nitrogen application rate(N 180 kg/hm~2),organic fertilizer nitrogen was set to replace 0%(OF0),50%(OF1)and 100%(OF2)of chemical fertilizer nitrogen application rate respectively,and no fertilization was used as the control(CK).Soil physical properties(bulk density,porosity,turbidity and moisture),chemical properties(p H,ECe,soluble ions,nitrate nitrogen and ammonium nitrogen content)and sunflower growth indicators(photosynthetic characteristics,ion absorption,etc.)were determined at different periods.The effects of combined application of organic and inorganic fertilizers on soil physicochemical properties and crop growth in saline soil were studied to provide a theoretical basis for the high-quality development of crop production in saline farmland in the HID.The main conclusions are as follows:(1)The combined application of organic and inorganic fertilizers can reduce the turbidity of soil solution,improve the soil porosity of 0-40 cm soil layer,reduce the soil bulk density,so as to improve the soil moisture content,adjust the soil effective water capacity,enhance the soil moisture conservation capacity,and improve the soil water environment in the crop root area.In two years,the soil moisture content of the treatment of organic fertilizer nitrogen replacing 50%chemical fertilizer nitrogen(OF1)increased by 5.34%,3.65%and 10.55%respectively compared with the treatment of single chemical fertilizer(OF0),the treatment of organic fertilizer nitrogen replacing 100%chemical fertilizer nitrogen(OF2),and no fertilizer(CK).(2)The combined application of organic and inorganic fertilizers can reduce the soil salt and soluble ion content,reduce the soil sodium adsorption ratio(SAR)and the cation ratio of soil structural stability(CROSS).At the same time,it is conducive to regulating the soil nitrogen supply capacity during crop growth period and improving the salt and nutrient status of crop root zone.At the end of two seasons of sunflower growth,the average soil ECe of0-100 cm soil layer in OF2 treatment was 6.77 d S/m,which was 44.10%and 11.61%lower than that in OF0 and OF1 treatment,respectively.In 2020,the soil mineral nitrogen content(sum of ammonium and nitrate nitrogen content)of OF1 treatment in 0-40 cm soil layer increased by 34.81%and 2.93%compared with OF0 and OF2 treatment.(3)The treatment of organic fertilizer nitrogen instead of 50%chemical fertilizer nitrogen(OF1)can improve the net photosynthetic rate of sunflower in vigorous growth period,reduce the salt cations content of aboveground plants in harvest period,improve the plant height,leaf area,yield,water and nitrogen use efficiency of sunflower,and increase the net income.Compared with OF0 and OF2,OF1 treatment increased yield by 9.47%and 7.52%respectively,increased water use efficiency by 17.50%and 9.52%respectively,increased agronomic efficiency of applied N by 29.23%and 28.24%respectively,increased partial factor productivity of applied N by 9.30%,and increased net income by 7.02%and 23.12%respectively.Therefore,in the high saline soil area of HID,considering the soil physical and chemical properties,Sunflower growth and yield,water and nitrogen utilization efficiency and cost-effectiveness in the growth period,it is suggested to use organic fertilizer nitrogen instead of50%chemical fertilizer nitrogen in sunflower production under the same nitrogen application rate(N 180 kg/hm~2).