Study On The Characteristics Of Soil Moisture Avriation In Karst Hillslopes And Terraces

In the southwestern part of China,the slower middle and lower sections of the peak cluster slopes have been developed as terraces for agricultural production.After the slope land was transformed into a terrace,the soil moisture changed greatly in terms of spatial and temporal distribution and rainfall infiltration.Therefore,the comparative study of soil moisture in the hillslopes and the terraced land in the karst area can further understand the soil moisture change on the karst slope.The process provides scientific guidance for the rational deployment of soil and water conservation measures and prevention of rocky desertification in karst areas.So this paper selected the slope of the typical karst peak cluster and used grid method measure the soil moisture content in the dry season?December?and the rainy season?May?,and the spatial variability of soil moisture on hillslopes was analyzed by geostatistics,to reveal the spatial variability characteristics of surface soil moisture.The infiltration process of different soil layers?0⁶0cm?in shrub land?natural slope?and terraced dry land?artificial terrace?was determined by ring infiltration method.The factors influencing infiltration were analyzed and different infiltration models were used.The process was fitted to determine the infiltration characteristics of the karst peak sloping soil.At the same time,using the hydrogen and oxygen stable isotope technique,combined with the long-term?2018.03-2019.01?dynamic monitoring of soil water content,to discuss the characteristics of water dynamics and migration mechanism of natural slopes and artificial terraces.The main conclusions are as follows:?1?Compared with the slope of single land use,the surface soil water content of the typical peak-cluster hillslopes is that undisturbed natural vegetation area located above the slope is significantly higher than artificial transformation of the region located below the slope,soil water content of sloping woodland?32.81%?that locating on top of the slope and undisturbed was significantly higher than terraced fields?24.2%?and terraced orange garden?20.0%?,terraced vegetable garden?22.0%?,bare land?23.5%?during the dry season.Compared with the dry season,bare land?30.2%?and terraced origin garden?32.1%?had increased obviously and the terraced fields were drastically reduced?17.9%?in the rainy season,and sloping woodland?32.2%?was still the highest.The spatial structure ratio is 21.0%and 8.7%during the dry and rainy season,indicating that the spatial correlation of the rainy season is better;The coefficient of variation of the surface soil moisture was 20.1%and 31.7%during dry season and rainy season,both belonging to moderate spatial variability;The range of surface soil moisture during the rainy season?77.5m?was significantly higher than that during dry season?8.0m?,it can be seen that the spatial variation structure of rainy season is better.The change of soil moisture in the surrounding space of bare stone decreases with the increase of distance;soil moisture in the surrounding space of terrace bank was decreasing with increasing distance.?2?Shrud land have better infiltration performance than terraces,and the average infiltration coefficient?0.66?of terraces is about 78.6%of shrud land?0.84?.The average initial infiltration rate and average stable infiltration rate of terraces at30cm⁶0cm are only 4.3%and 4.4%of the shrud land respectively,there is distinct infiltration barrier in the terraced at 30⁶0cm soil layer,and the reason is mainly composed of three:Firstly,terraces land itself has enough soil clay content;Secondly,artificial tillage will make the upper and lower soil mix,so that the finer particles easily down the soil pore migration;Lastly,under the action of gravity,the soil is transported or migrated to the underground space by creeping,collapsing,along the path of the dissolving channel that developed along the surface of the bedrock.The infiltration properties of shrub land and terraced fields are significantly correlated with soil properties.The contents of sand and organic matter in the shrub land were significantly higher than those in the terraced fields.The differences of soil properties between different soil layers in shrub land are not distinct,while the soil properties of 0³0cm and 30⁶0cm soil layers in terraced farmland are obviously different,which means the soil bulk density of the lower layer is very large and the soil porosity is small.The fitting effect of Horton model on shrub land and terraced farmland is better,and the general accuracy of the general infiltration model is better than the lower one,while the Kostiakov model and Philip model are poor.Infiltration models can better reflect the different infiltration processes.?3?The atmospheric precipitation line in the study area is?D=7.85?¹⁸O+19.02.Compared with the global atmospheric precipitation line,the slope is close but the intercept is too large.The preferential flow dominates the water transport in the soil profile of terraces,and the displacement of soil water on hillslopes is not obvious.The soil structure of the soil layer changed after the slope was changed.When the terrace was constructed,the upper layer of soil was mixed with the lower layer of sand.Part of the gravel was buried,resulting in the increase of deep sand,the ratio of clay content was significantly reduced,and the content of gravel was higher.The saturated hydraulic conductivity of the terraces is significantly higher than that of the hillslopes.As the soil depth deepens,the saturated hydraulic conductivity of the terraces decreases.