Study On The Laws Of Moisture Movement And Dissipation In Cavity Loess

On the one hand,the Loess Plateau in western China has severe drought and water shortage.On the other hand,concentrated rainfall in the form of heavy rains and rainstorms in summer from July to September each year is mostly lost in the form of torrents and surface soil evaporation,resulting in great waste of water resources.How to make full use of limited rainfall resources for agricultural production and improve the utilization rate of natural precipitation in arid areas is a problem many scholars are studying.The Cavity-Making Technology is to use micro blasting and other methods to form a cavity inside the soil.The upper layer of the cavity is loosened,which can absorb more moisture into the soil and reduce runoff losses.The lower layer of the cavity is compacted,which can form a relatively aquifer layer,blocking the leakage of water to the deep layer,preventing the lower groundwater capillary from rising and evaporating,and finally playing the role of promoting infiltration and reducing evaporation and water collection,which can be better used valuable precipitation resources.This paper uses a combination of laboratory experiments and HYDRUS software numerical simulation to simulate the law of water migration,storage and dissipation in the loess of the cavity structure under heavy rain,and also analyzes the influence of the cavity structure on the fertilizer transport.The following research results have been achieved:?1?Nash-Sutcliffe efficiency coefficient?NSE?,root mean square error?RMSE?and relative error?RE?were selected to analyze the moisture front and soil moisture content to evaluate the accuracy of HYDRUS model simulation.Finally,it is concluded that the HYDRUS model is constructed reasonably,and the simulation effect of the model is good.The HYDRUS software can simulate soil moisture infiltration under heavy rains.?2?Analysis of water migration law in cavity loess?.The existence of the cavity structure can reduce the depth of migration of the wetting front.The depth of the wetting front in the cavity group is reduced by 3 cm compared with the control group,and the reduction is 4.5%.After numerical analysis,the depth of the wetting front has a power function relationship with time.?.In the stage of water passing through the cavity layer,the wetting front of the control group moved faster than the cavity group,with an average height of 0.42 cm/h.The Philip model and Kostiakov model were selected to couple the infiltration process.The results show that the Philip model has better accuracy and applicability for the infiltration test in this paper.?.The influence of the cavity structure on water migration is reflected in the decrease of the infiltration rate when water infiltrates through the cavity layer.The cavity structure has the effect of"attracting"and"intercepting"water,which is conducive to storing water in the cavity layer.?3?Analysis of the effect of water storage and dissipation in cavity loess?.From the perspective of soil water content,the soil water content of the 30 cm and45 cm sections of the cavity group is higher than that of the control group,and the soil water content of the cavity layer is 1.6%higher than that of the control group on average.At the 60 cm section?below the cavity layer?,the soil water content of the cavity group was 2.4%lower than that of the control group.?.From the perspective of soil water storage,the water storage capacity of the 0-45cm soil layer in the cavity group is 133.65 mm,and the corresponding value in the control group is 127.65 mm,compared with 6 mm higher in the cavity group.The cavity structure increases the soil water storage capacity by 4.7%.?.The existence of the cavity structure reduces the soil evaporation intensity under the cavity,so it can reduce soil water evaporation and retain more water in the soil.At the end of the evaporation test,the cumulative evaporation of the cavity group was 37.45 mm,and the cumulative evaporation of the control group was 42.85 mm.In contrast,the cavity group had less evaporation of soil by 5.4 mm and reduced soil moisture evaporation by12.6%.It has the effect of inhibiting soil evaporation.?4?Analysis of the influence of cavity structure on soil fertilizer?.The change trend of fertilizer content with soil depth is consistent with the change trend of soil moisture content with soil depth,indicating that fertilizer content migrates with water,and also confirms that the cavity structure affects the migration of fertilizer content by affecting soil moisture infiltration.?.Compared with the control group,the concentration of fertilizer in the cavity layer is greater.The presence of the cavity structure can increase the NO₃^--N storage volume of the cavity layer by 16.4%and the NH₄⁺-N storage volume by 15.97%.?.Taking wheat as an example,the 0-40 cm soil layer has more roots,and the cavity structure can retain more fertilizer in the soil layer with the most crop roots,which is more conducive to reducing the loss of soil fertilizer.It is beneficial for the crop root system to absorb fertilizers,improve crop utilization efficiency of chemical fertilizers.