Study On Regular Pattern And Threshold Of Soil Evaporation Of Arid Area In Central Ningxia

In the arid regions of central Ningxia,there is little annual precipitation and severe evaporation.Strong evaporation is the main factor restricting the development of the local agricultural ecology and water shortage is the biggest trouble for local agricultural development In order to solve it,people adopt a farming model of soil surface mulched with gravel to reduce evaporation and save soil water.At the same time,it is particularly important to clarify the laws of soil evaporation in this area,find out the annual water income status of the soil reservoir and quantitatively calculate the ampunt of soil evaporation in the area.This paper combined the actual situation,comparative analyzes the difference between gravel-mulched land and bare land under the same conditions when studying soil evaoporation.On the foundation of the outdoor experiments,the following aspects have been achieved:(1)We set up simulated rainfall experiments with different rainfalls outdoors and copmeres the similarities and differences of the evaporation process between bare land and gravel-mulched land.At the same time,we analyzed the changes of temperature and soil moisture of different soil layers during the evaporation process.The results show that there is a big difference between the soil evaporation process of the bare land and gravel-mulched land.During the evaporation process,the cumulative evaporation of gravel-mulched land changes linearly with time,while the bare land has a logarithmic relationship.It was found that the temperature of each soil layer is higher than bare land when there is no rainfall.And we can see that the temperature of most gravel-mulched land soil layers is still higher than bare land expect for some soil layers when they were under simulated rainfall.For example,under simulated 10 mm rainfall conditions,the gravel-mulched land soil temperature only at 5 cm is lower than bare land;under simulated 15 mm rainfall conditions,the gravel-mulched land soil temperature only at 10 cm is lower than bare land;under simulated 20 mm rainfall conditions,the gravel-mulched land soil temperature only at 10-15 cm is lower than bare land.Through the analysis of the change process of the moisture content of each soil layer during the test,we can see that the surface soil has a greater response to evaporation,and the deep soil has a smaller response.The variability of the moisture content of each soil layer also decreases accordingly.(2)In order to solve the problem that how to make a quantitative calculation of soil evaporation in this area,we were committed to find the relationship between water surface evaporation and soil moisture in the study area through outdoor soil column experiments.Finally,an empirical formula for calculating soil evaporation in this area with water surface evaporation and soil moisture content as independment variable was established,and on this basis,the critical soil moisture content of the three stages of soil evaporation in the study area was determined.It has been tested that the formula can calculate the soil evaporation in the study area well and provides a reference for the quantitative calculation of soil evaporation in this area.At the same time,the bare soil evaporation can be divided into three stages according to the changes of the ratio of soil evaporation to water surface evaporation with time and soil water content.This paper gives the two critical values of water content in the three stages as 20.96%<?b1<21.48%and 11.40%<?b2<11.54%.In the same way,the soil evaporation in sand compaction can be divided into two stages,and the critical value of water content is 20.81%<?g<21.47%.(3)Under the simulated dry year rainfall condition,the annual evaporatioon of bare land is 160.88mm,and the annual income of the soil reservoir is-13.44mm.Under the simulated normal year rainfall condition,the annual evaporatioon of bare land is 171.44mm,and the annual income of the soil reservoir is 7.62mm.Therefore,it can be known that the threshold of the water revenue of the bare soil soil reservoir should be between 147.88mm and 179.06mm.Under the rainfall conditions set in this experiment,the moisture content of the soil reservoir in the gravel-mulcned land is all positive income,so according to the analysis of the minimum rainfall condition set in this experiment,the threshold of the moisture income of the soil reservoir in the gravel-mulcned land should be less than 147.88mm.These content are valueable for the research of soil evoparation,farmland water management and water resources distribution in the arid regions of central Ningxia.What's more,they also provide the theoretical basis for agricultural development and environment governance in this area.