Numerical Simulation Of Soil Water,Salt And Nutrient Transport In Cotton Fields In Different Oasis Irrigation Areas

Hydrus-1D model is an effective tool to simulate water and solute transport.In order to explore the spatial heterogeneity and transport characteristics of soil water,salt and nutrients in different oases,the transport changes of soil water,salt and nutrients under different drip irrigation or fertilization rates were studied.In this study,the Piedmont oasis,artificial plain oasis and desert transition zone in Manas River Basin were selected as the study area,and the soil under film drip irrigation of different oases was taken as the research object.Soil samples were collected in Piedmont oasis,artificial plain oasis and desert transition zone from May to October2019 for soil water,salt and nutrient analysis.From May to August 2021,the soil of cotton field was monitored and collected in 150 regiment farms in desert transition zone,Environmental factors were measured and recorded.The hydrous-1d model is used to simulate the soil water,salt and nutrient transport characteristics in the Piedmont oasis and desert transition zone from May to August 2019.The hydrous-1d model is used to analyze the change characteristics of soil salt in 150 regiment cotton fields in the desert transition zone under drip irrigation of 300m~3/ha~2 and 600m~3/ha~2,and the transport characteristics of soil ammonium nitrogen and nitrate nitrogen under fertilization of8kg/mu and 18kg/mu of urea.This has important guiding significance for the sustainable development of cotton field under film drip irrigation in arid area.The main conclusions are as follows:(1)The variation intensity of soil water,salt and nutrients in Piedmont oasis,artificial plain oasis and desert transition zone belongs to medium or strong variation.Soil moisture and salt content increased with the deepening of soil layer in the vertical section,and there was no obvious trend of soil ammonium nitrogen and nitrate nitrogen in each soil layer.The dominant factors of variation are soil type,climate and groundwater level.Drip irrigation and fertilization are important human factors affecting the distribution of soil water,salt and nutrients.(2)Hydrus model can be used to simulate the water,salt and nutrients of cotton soil under film drip irrigation in different oasis irrigation areas.From May to August2019,the simulated changes of soil water,salt and nutrients in 0-5,5-10 and 10-20cm soil layers fluctuated greatly,and the changes of soil water,salt and nutrients in 20-40and 40-60cm soil layers were relatively stable.By comparing the two indexes of Nash efficiency coefficient and root mean square error,it is found that there are some differences in the simulation effects of different soil layers.In the vertical section,the nse of soil water,salt and nutrients in the shallow layer of 0-5 and 5-10cm is less than that in the deep layer,indicating that there are many interference factors in the shallow soil.In the horizontal direction,the simulation effect of drip irrigation belt is better than that of bare land between films.On the whole,the simulated and measured values of soil water,salt and nutrients are basically consistent.The average Nash efficiency coefficients of soil water,salt and nutrients in Piedmont oasis and desert transition zone are water>ammonium nitrogen>nitrate nitrogen>salt.The model can reflect the changes of soil water,salt and nutrients in different layers in different oasis irrigation areas with time.The model can be used to simulate the dynamic changes of soil water,salt and nutrients in drip irrigation farmland under film in arid area.(3)The numerical simulation of hydrous migration shows that during the growth period from May to August,it fluctuates in a zigzag manner with drip irrigation and fertilization,and the salt content shows a downward trend during the growth period.In the late harvest,in October,the soil moisture,ammonium nitrogen and nitrate nitrogen of cotton fields in different oasis irrigation areas showed a downward trend,and the salt showed a downward trend.At the flowering and Bolling stage of cotton,the fluctuation of soil moisture at 20-40 and 40-60 cm was weaker than that at the emergence stage.(4)Hydrus simulation shows that different drip irrigation rates have obvious differences in the reduction of soil salt.Compared with before and 10 days after drip irrigation,under the drip irrigation rate of 300m~3/ha~2,the soil salt under the drip irrigation belt decreased by 14.25%,the bare land between films decreased by 8.09%,and the soil salt under the drip irrigation rate of 600m~3/ha~2 decreased by 32.93%.Compared with before and 9 days after drip irrigation,under the fertilization rate of8kg/mu of urea,the soil ammonium nitrogen decreased by 50.46%,the nitrate nitrogen increased by 18.47%,the soil ammonium nitrogen decreased by 31.78%,and the nitrate nitrogen increased by 39.66%;Under the fertilizer application rate of 18kg/mu of urea,the soil ammonium nitrogen increased by 5.31%and nitrate nitrogen increased by137.20%.Soil ammonium nitrogen decreased by 19.25%and nitrate nitrogen increased by 189.3%.