Study On The Effect Of Biochar On The Water Movement Process Of Yellow Soil In Karst Area

Guizhou Province is a typical karst landform distribution area,and karst landform accounts for61.9%of the total area of the province.This area belongs to the subtropical monsoon humid area,with abundant rainfall,but the temporal and spatial distribution of rainfall is uneven.At the same time,due to the relatively developed rock fissures and waterfall holes,the rainfall is rapidly infiltrated,and the utilization of water resources is difficult.Yellow soil is one of the main soil types in Guizhou,accounting for the largest soil area in the province,with sticky,acid,thin,drought-resistant characteristics.The adsorbed water on the surface of yellow soil clay particles and the ineffective water absorbed by the aggregates account for a large proportion of soil water content,resulting in low effective water content,poor water and fertilizer retention,and low land utilization rate,resulting in low agricultural yield.Therefore,improving the water holding capacity of yellow soil and improving the water availability of yellow soil are of great significance to agricultural production in Guizhou Karst area.Because of its special physical and chemical properties,biochar plays an important role in improving soil structure and soil water and fertilizer retention.Therefore,based on the indoor soil column simulation experiment,the effects of biochar on the hydrodynamic characteristics of yellow soil were studied at the microscopic laboratory scale,and the effects of different types(corn straw biochar and rice husk biochar),different contents(0,1%,2%,3%)and different particle sizes(<0.25 mm,0.25-1 mm,>1 mm)of biochar on the infiltration,evaporation and water holding characteristics of yellow soil were discussed under the condition of constant bulk density.The applicability of Kostiakov model,Horton model and Philip infiltration model was compared and evaluated.The results can enrich the understanding of biochar in soil hydrological effects,and provide a useful reference for the efficient utilization of agricultural organic waste resources and water and soil resources in karst areas.The main research results are as follows:(1)The addition of Corn Straw Biochar(CSB)and Rice Husk Biochar(RHB)significantly inhibited the water infiltration of karst yellow soil under the condition of constant bulk density.The higher the addition of CSB and RHB was,the lower the cumulative infiltration of soil was and the slower the wetting front process was.The particle size of the two biochars had a significant impact on the infiltration process of karst yellow soil,showing that the inhibitory effect of large-size biochar on soil infiltration was significantly higher than that of small-size biochar.Horton model and Kostiakov model are suitable for the simulation of soil water infiltration process in this study.Horton model has high fitting accuracy,while the initial infiltration rate obtained by Kostiakov model is closer to the measured results.Adding CSB and RHB,the simulated and measured values of soil infiltration rate fitted by Horton model can be expressed as=1.5063-0.0244(~2=0.99)and=1.7295-0.0555(~2=0.99),respectively.(2)Adding proper amount of biochar with proper particle size can inhibit soil evaporation and effectively reduce soil moisture evaporation.The addition of CSB and RHB with small particle size(<0.25 mm)has an inhibitory effect on the cumulative soil evaporation,and the addition of medium particle size(0.25-1 mm)and RHB with large particle size(>1 mm)has an effect on cumulative soil evaporation.The addition of low content(1%)of CSB and RHB can inhibit the cumulative soil evaporation,and the addition of high content(3%)of CSB and RHB can promote the cumulative soil evaporation,The promotion effect,as the amount of biochar added increases,the particle size increases,and the effect of promoting evaporation becomes more obvious.After adding CSB and RHB,the water content of yellow soil was increased,the release time of water was prolonged,the early soil evaporation process was inhibited,and the later soil water evaporation was promoted.(3)The addition of biochar significantly reduced the soil bulk density.With the increase of the addition amount,the soil bulk density decreased,while the total soil porosity and capillary porosity increased.Field Moisture Capacity(FMC)increased by 5.30%and 4.72%,Field Water Holding Capacity(CWC)increased by 4.75%and 6.60%after adding CSB and RHB.The change of soil saturated hydraulic conductivity was related to the particle size of biochar.Adding CSB and RHB with particle size<0.25 mm,the soil saturated hydraulic conductivity decreased by 11.74%and21.74%.Adding CSB and RHB with particle size>1 mm,the soil saturated hydraulic conductivity increased by 66.67%and 33.33%.Adding biochar with particle size 0.25-1 mm,the soil saturated hydraulic conductivity had no obvious change.Adding biochar can significantly reduce soil bulk density,improve soil field capacity and capillary capacity,and improve soil water conductivity.