| The rapid leakage of soil moisture is one of the important reasons for the drought of karst ecosystem,and the study of its water transport process has become the focus and frontier in this field.In the serious rocky desertification area,the exposed rock and soil are interlaced,which increases the complexity and heterogeneity of water movement in the area.The rock-soil interface,as a special interface between exposed carbonate rock and soil,has an important effect on soil water movement.However,the process of soil water transport may be different under different rock surface shapes with different confluence paths.Therefore,this study selected fallow land,arable land I（Zea mays）and arable land II（Zanthoxylum bungeanum+Zea mays）as the research object,by means of field investigation,in situ infiltration,staining and tracing,and indoor analysis.The relative drought and moisture conditions of soil were studied,the soil physical properties,water infiltration properties and preferential flow path characteristics of rock-soil interface under flat,convex,concave and random shapes were analyzed.In order to reveal the law of soil water movement and its influencing factors at the rock-soil interface in karst slope land.The research results can further deepen the understanding of rapid water leakage of rock-soil structure in karst area,and provide scientific basis for the implementation of national rocky desertification ecological engineering and soil and water conservation to a certain extent.The main results are as follows.（1）The content of clay and silt in the soil at the convex rock-soil interface is higher than that of the concave type,while the characteristics of sand content are opposite.The root length density and root surface area density of the soil at the rock-soil interface and non-rock-soil interface in fallow land are as follows:convex type>concave type>straight type,while there is no obvious pattern in cultivated land I and II.The natural moisture content of soil at rock-soil interfaces and non-rock-soil interfaces varies greatly under different shapes,with the convex type being the smallest.The natural moisture content of the 10-20cm soil layer at the rock soil interface and non rock soil interface is higher than 0-10cm,and the natural moisture content of the soil at the rock soil interface is generally higher than that at the non rock soil interface.The saturated water capacity of the 0-10cm soil layer at the rock soil interface and non rock soil interface under different shapes is greater than10-20cm,and the rock soil interface is smaller than the non rock soil interface,with the concave type being the smallest.The soil capillary water capacity at random rock soil interface and non rock soil interface is the highest;However,the soil capillary water capacity of the convex rock soil interface and non rock soil interface is larger under relatively dry soil conditions,but smallest under relatively humid soil conditions.The field water capacity of soil at the rock soil interface and non rock soil interface is generally the smallest in the convex type and the largest in the random type.（2）The results of disc infiltration show that the overall infiltration process of soil at the rock soil interface and non rock soil interface shows a downward trend,with an infiltration rate basically within 20mm·s-1and reaching a stable infiltration state for about 1 minute.The water infiltration curve of soil at the rock soil interface and non rock soil interface varies greatly under different negative pressure water heads.When the negative pressure head is-15cm,the decrease is significant(0.50-7.80mm·s-1);When the negative pressure head is-6cm,the downward trend is gentle(0-0.65mm·s-1).When the negative pressure water head is-3cm,the soil water infiltration process at the rock soil interface and non rock soil interface shows an overall upward trend(0-11.55mm·s-1);When the negative pressure water head is-0.5cm,the soil water infiltration process at the rock soil interface and non rock soil interface of fallow land generally shows a downward trend,while the trend of farmland I and farmland II is opposite under relatively dry and humid soil conditions.In this experiment,the soil had the highest number of small pores（0.01～0.025cm）and the largest pore ratio,followed by medium pores（0.025～0.05cm）and the smallest number of large pores（>0.05cm）,but their pore ratio was larger than that of medium pores.The main influencing factors of soil water infiltration at different shapes of rock soil interfaces and non rock soil interfaces are soil bulk density,macropores,micropores,and tillage methods（P<0.05）,followed by soil particles and rock surface shape（P>0.05）.（3）The straight rock surface has a relatively uniform water distribution and transport pattern.The outward convex rock surface flow is greatly affected by rock dispersion,and after entering the soil,it is easier for the outward convex rock surface flow to disperse to the surface layer（0-10cm）of rock surrounding soil.The water transport pattern between each section of the outward convex rock is"shallow in the middle,deep on both sides".The concave type has the function of converging rainwater flow,and after entering the soil,the water transport form is"deep in the middle,shallow on both sides".Most of the rock surface flow migrates along the rock soil interface to the deep soil in the form of rock soil interface flow,with a maximum depth of up to 110cm.The existence of cracks at the rock soil interface has a significant impact on the transport morphology of rock surface flow.As the depth of the soil layer deepens,the ratio of soil water infiltration area decreases linearly until it approaches 0.The soil moisture content greatly affects the infiltration area of soil moisture.After the rock surface flow enters the soil,the water transport area ratio decreases in a fluctuating manner as the depth of the soil layer deepens,and finally approaches 0 at a certain depth,reaching the endpoint of the rock surface flow transport. |
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