Effect Of Biochar On Water Infiltration And Redistribution Process Of Purple Soil

Purple soil is widely distributed in the hilly areas of southwestern and southern China,especially in the hilly areas of Sichuan and Chongqing and the low mountainous areas.It is also the most important soil type for agricultural land in Chongqing.However,due to the special soil-forming process of purple soil,the soil layer is shallow,the corrosion resistance is poor,and the soil erosion is serious.In addition,Chongqing is located in the subtropical zone of the upper reaches of the Yangtze River.The rainfall is large and concentrated,and the rainfall spatial and temporal distribution is very uneven,especially heavy rain and seasonal drought occurs frequently,resulting in serious soil erosion in purple soil slope farmland.Severe soil erosion not only removes nutrients from the soil,but also causes soil fertility decline and soil degradation,which restricts the sustainable development of Chongqing's agricultural economy.At the same time,soil erosion will carry a large amount of sediment and soil pollutants.To the Three Gorges Reservoir,the safety of the dam body that jeopardizes the Three Gorges Dam also brings agricultural non-point source pollution to the Three Gorges reservoir area and affects the water quality of the reservoir.Many scholars at home and abroad have conducted in-depth research on soil infiltration problems,but the research on the mechanism of soil infiltration in purple soil in southwest China needs to be strengthened,especially purple soil as the most important soil type for agricultural land in Chongqing,Chongqing.At the upper reaches of the Three Gorges reservoir area,the study of agricultural soil is more important.Secondly,the existing research on purple soil infiltration is mostly the study of soil pillars of pure purple soil.For the mixing of purple soil and biochar,It is still rare to study through different additions and addition methods.It is necessary to try to reduce the soil erosion of purple soil in the southwest by biochar,and establish a purple soil-biochar hybrid infiltration model.Therefore,this paper takes the biochar prepared from purple soil and rice straw in the purple soil test base of the School District of Southwest University of Beibei District,Chongqing as the raw material,and uses the indoor soil column infiltration test method to explore the purple soil,purple soil and biochar under different conditions.Infiltration and water redistribution of the mixture.It provides a theoretical basis for water transport in the typical purple soil region of Chongqing,also has important practical significance and practical value for reducing soil and water loss,preventing agricultural non-point source pollution and improving soil water holding capacity.The conclusions are as follows:(1)Soil bulk density and initial soil moisture content are direct influence parameters affecting soil infiltration.The larger the bulk density,the smaller the infiltration rate and the wetting front migration rate.The larger the initial water content,the smaller the initial infiltration rate and the stable infiltration rate,the larger the initial wetting front migration rate,the larger the steady wetting front migration rate,the shorter the time,and the smaller the cumulative infiltration.(2)Adding biochar can promote infiltration,but the addition of more than a certain range will hinder the progress of infiltration,promote the fastest infiltration and promote the fastest growth of the wet front.The amount of biochar added in the biochar is between 0%and 10%.The addition of biochar can promote the cumulative infiltration,but the promotion is firstly increased and then decreased with the addition of biochar,and the maximum amount of biochar added to accumulate the infiltration is between 5%and 15%.(3)At the end of infiltration,the distribution of soil moisture content in each soil layer is mainly the cumulative infiltration and soil depth.The continuity of the soil also affects the distribution curve of soil moisture content in each soil layer.The addition of biochar can reduce the evaporation loss of the soil,increase the water absorption capacity of the soil,enhance the water holding capacity of the soil,and reduce the soil moisture loss.At the same time,biochar promotes soil water retention in the middle and lower layers of the soil.(4)The difference of soil water redistribution under different biochar addition methods is significant.The addition of biochar in the upper layer has little effect on the distribution trend of soil moisture content in the vertical section.However,the addition of biochar to the lower layer changes the distribution trend of soil moisture content in the vertical section.The continuous homogeneous soil has a turning point where the soil moisture content increases to the maximum and then decreases in the depth range of 150mm~200mm.In this depth region,the soil has a high water content in a long period of time,which can sustainably supply water to plants and promote plant growth.(5)When the lower layer is added with biochar the water content of the lower layer soil is higher than all the biochar is added because of the water supplied by the upper layer soil quickly and more.In actual production,plants with large water requirements in deep roots can use bio-carbon in deep soil.When biochar is added to the upper layer,the boundary line of biochar addition is also the boundary line of soil moisture content.The moisture content of the upper layer soil is always higher than the lower layer.In actual production,the soil moisture content of the upper and lower layers can be separated by adding biochar to the upper soil.(6)The infiltration rate changes with time according to the power function relationship.Kostiakov function model and the Philip function model's fitting result R~2 are above 0.97 by using Origin 8.0 that the model accuracy and stability all high.However,the Kostiakov infiltration model has a better fitting goodness and can be applied to the prediction of instantaneous or stable infiltration rate.The Philip model is not suitable for the prediction of stable infiltration rate,and only applies to the prediction of instantaneous infiltration rate.