Numerical Simulation Of Soil Heat In Gravel-Mulched Fields

The thermal conditions of soil are important in practical agricultural production.The temperature of the soil tillage layer is important to the extreme growth of the crops,and reasonable regulation of the soil temperature is necessary for agricultural production.In this paper,VADOSE/W numerical simulation software is used to simulate the soil temperature,analyzing the thermal properties in sand-mulched soil,and this study provides a method of calculating soil heat flux by using soil temperature.Finally,the distribution law of soil temperature,temperature difference and temperature gradient in different periods of spring wheat during the whole growth period is revealed.The main contents are as follows:(1)We used VADOSE/W to establish a model of the transfer of heat between soil and the atmosphere,simulating the temperature of bare soil and sand-mulched soil in field experiment in Gaolan County,Xinjiang and Xigaze area of Tibet Autonomous Region.The results show that the correlation coefficient between the simulated value and the measured value is between 0.9496-0.9980,indicating a good fit and it can be used to analyze the test results.(2)VADOSE/W numerical simulation software is used to simulate the influence of constant heat source and external air temperature on soil thermal properties,obtaining the temporal and spatial distribution sequence of soil temperature.The finite-difference method and traditional sine method were used to analyze the soil thermal diffusivity and soil heat flux for bare soil and sand mulching.The results show that the daily changes in the temperature of soil for bare soil and sand mulching is sinusoidal at different depths with times,and tends to be stable in deep layers;The thermal diffusivity of soils for bare soil and sand mulching at different depths show a certain difference.Soil thermal diffusivity increases with increasing soil depth,and gradually stabilizes with the change of time for constant heat source.The heat flux of shallow soil changes more than that of deep soil.The change of soil heat flux with sand mulching is smaller than bare soil in daily temperature.Sand mulching can reduce the influence of external environment on the internal thermal properties of soil.(3)Numerical simulation was used study the temperature of soil in different growth periods of spring wheat during the growing season of spring wheat.The relationship between temperature and depth at 07:00 and 14:00 could be expressed by a linear or quadratic function.(4)Numerical simulation was used study temperature differences and a temperature gradient for sand mulching and bare soil during the growing season of spring wheat.and the temperature differences at each depth and in the gradient from 00:00 to 07:00 were positive during each stage of growth.These results indicated that the sand mulching preserved heat at night.The difference in temperature at each depth and the temperature gradient became negative with the gradual increase in solar altitude.The difference in soil temperature at each depth and the temperature gradient tended to become positive by 22:00.The range of the difference in temperature was within ±3°C,and the temperature gradient directly represented the vertical transfer of heat.These results indicated that the sand mulch effectively maintained the soil temperature in the morning and night during the growing season and impeded the transfer of heat at mid-day.It can provide theoretical guidance for the effective control of spring wheat soil temperature of gravel-mulched fields.