A Simulation Study On The Soil Hydrological Characteristics In The Bottom Layer Of Tillage And Plough In Shanxi Province

The bottom layer of plough is formed due to the extrusion of plough and the clay particles along with the water deposition during the long term cultivation and the precipitation.For the cultivation of soil,the plough bottom with appropriate thickness is beneficial to the development of agriculture,it can play a role in water and fertilizer conservation.However,the overthick plough bottom layer hinders the water transfer and supply between soil layers,affects the movement and distribution of soil water,and has a negative impact on the growing environment of crops.In recent years,due to the unreasonable farming practices,the plough bottom is commonly found in the cultivated soil.At the same time,with the gradual increase of global temperature in recent years,the occurrence probability of extreme weather is gradually increasing,and the traditional pattern of atmospheric rainfall has also changed.The characteristics of short and strong rainfall are very prominent.Especially in semi-arid and arid areas of China,extreme atmospheric rainfall increases the surface runoff,resulting in more floods,soil erosion,nutrient loss in farmland and a series of agroecological environmental security problems.Therefore,it is of great significance to explore the soil hydrological characteristics of the tillage layer and plough bottom layer,which is conducive to the soil hydraulic characteristics of farmland,the efficient utilization of agricultural water resources,and the effective response to agricultural production in extreme climate.In this paper,in Shanxi Province to collect all kinds of typical farming soil types of magnetism,select sixteen types soil as the tested soil,which can meet the full range of soil physical and chemical properties of soil on the determination of soil water characteristic curve,all kinds of soil physical and chemical properties is set up by regression statistical method under the decision of multivariate nonlinear prediction model of soil water characteristic curve.Based on the predicted soil water characteristic curve of each sampling point,the soil water constant and available soil water were estimated according to the critical value of matrix potential.Combining with the RETC software to fit the values of a and n of the soil hydraulic parameters in the van Genuchten model,the rainfall yield process under the setting of soil infiltration performance and different rainfall intensities in the tillage layer and plough bottom was simulated based on the hydrus-1d numerical model.Finally,the spatial distribution characteristics and trend changes of soil hydrology characteristics of plough bottom layer in Shanxi Province were predicted qualitatively and quantitatively by geostatistics.The results show that:1.The determination coefficient of the prediction model of soil water characteristic curve was 0.740,which passed the F test and t test.The mean relative error of the modeling sample and the verification sample is 14.460% and 13.237% respectively,both of which are about 10%.The RMSE value of the predicted value and the measured value is 0.67.The soil moisture characteristic curves of soil bulk density,texture and organic matter mass fraction in the prediction model were quantitatively expressed by virtual simulation.2.The field water capacity and wilting coefficient values of each layer of soil estimated by the prediction model were spatially interpolated with the ordinary kriging method,and the results showed an overall regional change trend,gradually decreasing from the southeast to the northwest of Shanxi Province.The difference between field water holding capacity and soil effective moisture content of cultivated soil was very significant at different levels(p<0.05),and the average value of field water holding capacity at the bottom of plough was significantly lower than that at the surface.In the western part of the study area,the soil under the plough has a large potential effective soil water volume.3.Taking the sampling point of wuxiang county as an example,during the infiltration process of fixed water head at the till-plough bottom,the rate of soil moisture content increase gradually slowed down with the gradual migration of water in the till-plough bottom.The advancing rate of the wetting front at the bottom of the plough is 0.066cm/h,which is much lower than the migration rate of the wetting front at the ploughing layer of 2.477cm/h.At the initial moment of infiltration,the infiltration rate was extremely high,reaching a maximum value of 1.32cm/h.Later,under the action of non-uniform section,the infiltration rate had a multilevel interaction effect,and the infiltration rate at various depths of the soil gradually tended to be consistent.At the end of infiltration,the section reached a stable infiltration rate of 0.02cm/h.4.The stable infiltration capacity of the uneven soil layer in the tillage layer-plough bottom showed a regional decline from northwest to southeast,and the coefficient of variation was 235.71%(highly unstable).Among all tillage soil types,the order of the stable infiltration capacity of the tillage layer to the bottom layer of the plow was: chestnut chestnut soil > chestnut soil > brown soil = primary soil > tide soil,the maximum value was 4.421cm/h,the minimum value was 0.02cm/h.5.The spatial interpolation results of the rainfall runoff simulation in Shanxi Province are directly affected by the rainfall intensity,and have similar spatial distribution characteristics under the four rainfall intensity,and the runoff gradually increases from northeast to southwest.Among all kinds of tillage soil types,the tillage layer of brown soil under four kinds of rainfall intensities--the bottom layer of plough soil yields the best results compared with other types of tillage soil,while the tidal soil is the worst.