Hydrological Process Of Karst Fissures And Resistance And Control Technology Of Soil And Water Loss In Agroforestry

Soil and water movement,soil erosion and resistance and control of soil and water loss in karst rocky desertification area are hot issues in current research.The extensive development of shallow fissures near the surface provides an important channel for soil and water migration,and forms a unique form of soil and water loss,resulting in the complexity of spatial and temporal combination of soil and water resources.Therefore,it is of great significance to strengthen the research on the law of soil and water movement in karst fissures and the resistance and control of soil and water loss in agroforestry,so as to scientifically promote the resistance and control of soil and water loss and rocky desertification in karst areas and promote the development of agroforestry industry.According to the theories of geography,ecology,hydrology and so on,such as soil and water loss,soil and water conservation,runoff control,agroforestry intercropping and agroforestry measures,this paper aims at the scientific issues and technical requirements such as wide development of karst fissures,strong spatial and temporal heterogeneity of hydrological process,complex influencing factors of soil and water loss,and urgent need for research and development of the resistance and control technology of soil and water loss in southern China.In Guizhou plateau mountainous area,which represents the overall structure of karst rocky desertification ecological environment in South China,three types of karst ecological environments were selected as the research areas: Bijie Salaxi of potential-slight rocky desertification of plateau mountain,Guanling-Zhenfeng Hua Jiang of moderate-intensity rocky desertification of plateau gorge and Shibing of non-potential rocky desertification of mountain gorge.In 2018?2021,through comprehensive field investigation,investigation of vegetation types near the surface of fissures,determination of soil physical and chemical properties and water holding capacity,monitoring of soil moisture and rainfall,using in-situ monitoring,laboratory experiments,variance analysis,correlation analysis,comparative analysis and other statistical methods,systematic research is carried out on the basic frontier research of hydrological process of karst fissures,soil properties,soil and water loss,common key technology research,development,application,demonstration and promotion of the resistance and control technology in agroforestry.In addition,this paper analyzes the dynamic characteristics of soil moisture,the influencing factors and the water supply characteristics of fissures under different rainfall events,focuses on the temporal and spatial variation law of soil moisture of fissures,reveals the interaction mechanism among various influencing factors of hydrological process of fissures,integrates and constructs the resistance and control technology of soil and water loss of fissures in agroforestry,and carries out application,demonstration and verification.It can provide scientific and technological reference for the comprehensive management of karst rocky desertification and rural revitalization at national and local levels.(1)The vertical distribution of soil moisture showed that soil moisture of the lower layer was higher than the upper layer,and the deep layer soil had better water storage capacity.The degree of variation and activity of soil moisture in fissures in rainy season were higher than that in dry season.During the monitoring period,the highest of average soil moisture of BJ-1,BJ-2 and BJ-3 in the Bijie Salaxi study area was respectively appeared in 80 cm layer(37.83%),20 cm layer(21.72%)and 160 cm layer.The highest of average soil moisture of HJ-1,HJ-2 and HJ-3 in GuanlingZhenfeng Huajiang study area was respectively appeared in 160 cm layers(30.86%),40 cm layers(31.21%)and 160 cm layers(30.93%).In Shibing karst research area,the highest of average soil moisture of HC-1,HC-2 and HC-3 was respectively appeared in 80 cm(30.98%),160 cm(31.95%)and160 cm(21.98%).In addition,the variation coefficient of soil moisture in fissures showed that except for BJ-2 and BJ-3,the degree of activity and variation of soil moisture in other fissures were higher in rainy season than in dry season,and the hydrological process of fissures was more intense in rainy season.(2)There were differences in soil properties of each fissure in the same study area.The soil bulk density and the content of clay of fissures increased with the depth of soil layer,while the total porosity,water holding capacity,the content of sand and silt decreased.Soil bulk density,total porosity,maximum water holding capacity between BJ-1,BJ-3 and BJ-2 were significantly different(P<0.05),and field water holding capacity between BJ-1,BJ-2 and BJ-3 were significantly different(P<0.05)in Bijie Salaxi study area.There were no significant differences in soil capillary water holding capacity among the three fissures(P>0.05),and there were no significant differences in soil bulk density,total porosity and field water holding capacity among three fissures in Guanling-Zhenfeng Huajiang study area(P>0.05).There were significant differences in capillary water holding capacity and maximum water holding capacity between HJ-1 and HJ-3(P<0.05).There were no significant differences in soil properties and water holding capacity among three fissures in Shibing karst study area(P>0.05).(3)The soil particle composition of fissures was mainly silt,and the content of silt was positively correlated with soil erodibility K value,the total soil porosity and the field water holding capacity were positively correlated with the spatial and temporal variation characteristics of soil moisture of fissures(P<0.05).The average content of sand,silt and clay of fissures in Bijie Salaxi study area were 32.99%,34.18% and 32.82%,in Guanling-Zhenfeng Huajiang study area were 21.39%,47.86% and30.42%,and in Shibing karst study area were 36.62%,40.35% and 23.02%.In the three study areas,except for HJ-1 and HC-3,the erodibility K value of fissures was significantly positive correlated with the silt content(P<0.05).There was positive correlation between the vertical variation coefficient of soil moisture and the vertical variation coefficient of total porosity(P<0.01).The variation coefficient of soil moisture in rainy season was significantly positively correlated with the vertical variation coefficient of total porosity and the field water holding capacity(P<0.05).(4)There was an obvious response relationship between the variation curve of soil moisture of fissures and the distribution characteristics of rainfall events.Rainfall intensity,rainfall amount and vegetation types affected the hydrological variation and the characteristics of soil moisture supply of fissures.In the events of low rainfall and small rainfall intensity,the variation curve of soil moisture of fissures was stable,the increase range was small,and the effective recharge capacity,effective recharge rate and effective recharge efficiency of soil moisture of fissures were small.In the event of heavy rainfall and high rainfall intensity,the soil moisture of fissures increased obviously,the lag time shortened,and the effective recharge capacity,effective recharge rate and effective recharge efficiency were greatly improved.The same rainfall event had different recharge characteristics for different types of fissures,indicating that the hydrological process of fissures was affected by the near-surface vegetation types of fissures.The same rainfall event also had different recharge characteristics for the shallow soil moisture(0-40 cm)and deep soil moisture(40 cm-160 cm)of fisstures.There was a phenomenon that the recharge characteristics of deep soil moisture was higher than that the shallow soil moisture and the lag time of deep soil moisture was shorter than that the shallow soil moisture.(5)Through the application,demonstration and verification of the water conservation technology of agroforestry,spatial closure technology of agroforestry and intercropping technology of agroforestry,it is beneficial to improve the soil structure,prolong the lag time,and slow down the speed of water migration in the soil.The resistance and control technology of soil and water loss in agroforestry requires adjusting the structure of vegetation near the surface of the fissures,improving the nature of the fissures soil,and reducing the erosion of the soil.Based on this,the water conservation technology of agroforestry,spatial closure technology of agroforestry and intercropping technology of agroforestry were used in the demonstration site to increase the vegetation coverage near the surface of fissures.At the same time,plant roots were used to improve the soil structure and enhance the absorption and utilization of soil and water,and the canopy was used to intercept rainfall,so as to play the role of plants in soil and water conservation.The future research needs to explore the feasibility and scientificity of resistance and control technology in agroforestry in other soil and water loss links,so as to realize the optimization and maximization of benefits of resistance and control technology of soil and water loss in agroforestry.