Study On Water And Salt Distribution And Nitrogen Migration In Cotton Field In Saline Alkali Soil

Xinjiang is located in the inland arid area of Northwest China,with dry climate,less rainfall and large evaporation.Since the mid-1980s,the rapid development of oasis irrigation agriculture has led to a large area of land secondary salinization.Generally,increase the irrigation quota,or even flood irrigation to wash the salt,reduce the concentration of soil salt in the plough layer,or use water conservancy methods such as shaft and concealed pipe to wash and drain salt,so as to ensure the normal growth of crops.However,with the implementation of the three red lines of water resources,land irrigation quota is strictly controlled.Strict irrigation quota is difficult to guarantee the water and salt regulation,so as to ensure the normal growth of crops.Nitrogen is an essential element for crop growth and development,and it is the basis for the synthesis of substances in crops.It can alleviate salt damage,affect growth and yield.However,under the specified irrigation quota,it is of great significance to study the effect of salt and nitrogen on soil water,salt and nitrogen distribution and nitrogen accumulation and utilization of cotton.Cotton Xinluzhong 68was used as material.The soil salt content was S1(2.5-3 g/kg),S2(5-6 g/kg)and S3(8-9 g/kg),and the nitrogen application rates were N1(105 kg/hm²),N2(210 kg/hm²)and N3(315 kg/hm²),respectively.The soil water and salt distribution was analyzed by Hydrus model and the biomass nitrogen accumulation of each organ was fitted by logistic growth function model.The effects of salt and nitrogen on soil water,salt and nitrogen distribution characteristics,cotton biomass nitrogen accumulation characteristics and cotton growth were analyzed,which provided a theoretical basis for rational use of saline alkali soil and fertilizer management.The main conclusions are as follows(1)According to the analysis of soil water and salt data,the downward migration speed of water in low salt soil is faster,and the water holding capacity is relatively poor;The water infiltration rate of medium and high salinity soil is relatively low,and the water holding capacity is relatively good.In terms of nitrogen,there was no significant difference among the three treatments,but the increase of nitrogen increased the salt difference between adjacent soil layers,and promoted the accumulation of salt from the upper layer to the surface layer and the bottom layer.(2)Hydrous was used to simulate the soil water and salt transport,and the results showed that the measured values were in good agreement with the simulated values.The simulation results showed that soil salinity had a significant effect on water and salt movement in different soil depths.During the growth period,the salt content of bare land outside the film continued to accumulate,while the soil inside the film slowly and continuously desalting.(3)Through the analysis of soil nitrogen data,nitrate nitrogen(NO_-3-N)decreased significantly(P>0.05)and ammonium nitrogen(NH₄⁺-N)increased significantly(P>0.05)with the increase of soil salinity.In the distribution of NO_-3-N,18.5%-33.8%of the soil surface layer was accumulated in large amount,and it decreased with depth.NH₄⁺-N also accumulated in the surface layer of soil,accounting for 14.8%?27.82%.In the 10-60 cm soil layer,the distribution of NH₄⁺-N from seedling stage was gradually gentle with the growth period,and the peak value moved downward.(4)According to the data analysis of experiment and logistic growth function model,the increase of salinity significantly inhibited the biomass and nitrogen accumulation of cotton organs and the maximum accumulation rate V_m(P<0.5).There was a significant interaction between nitrogen application and soil salinity.Nitrogen fertilizer in S1 and S2,N2 and N3 in S3 were the most favorable for reproductive organ biomass accumulation and rate V_m.The higher the salinity,the lower the nitrogen translocation rate.The nitrogen application rate promoted the nitrogen transport rate.The accumulation of nitrogen accumulation in various organs and the distribution of nitrogen in vegetative organs make the distribution of nitrogen more balanced,leading to the optimal yield.(5)Through the measurement and analysis of the growth characteristics of experimental crops,the increase of soil salinity significantly inhibited the growth and yield of cotton,and lagged behind the growth.The inhibition effect on plant height,leaf area index,dry matter weight,effective number of flowers and Bolls and yield reached 2.31%?38.78%,23.91%?49.14%,4.9%?51.47%,2.3%?38.76%and20.03%?75.46%.Nitrogen application significantly alleviated salt damage and promoted cotton growth and yield.The effects of nitrogen fertilizer on plant height,leaf area index,dry matter weight,effective number of flowers and Bolls and yield were 1.9%?8.6%,4.09%?25.6%,33.61%?61.61%,30.71%?65.63%and 2.47%?212.05%,respectively.With the increase of soil salt content,the effect of nitrogen fertilizer on yield was more significant.(6)Through the yield measurement and nitrogen use efficiency calculation and analysis,the maximum yield of s1n2 reached 6683 kg/hm².In S1 and S2,N1 treatment had the best nitrogen use efficiency,while in S3,N2 treatment had the best nitrogen use efficiency.Therefore,applying 105 or 210 kg/hm²nitrogen fertilizer in soil with salinity less than 6 g/kg is most beneficial to cotton production and benefit.315kg/hm²of nitrogen fertilizer should be applied when the soil salinity is 8-9 g/kg.