Spatial Heterogeneity Analysis Of Soil Water-Fertilizer Under Different Land Use Patterns In Dry-Hot Valley Of Typical Karst Area

Karst landforms are widely distributed in southwest China,among which karstification is the strongest.Because most of the weathered materials are washed away by various forms of precipitation,the soil in this area is shallow and discontinuous,and there are many rock fragments.At the same time,the process of redistribution or loss of carbon,nitrogen and phosphorus mineral elements in the soil due to strong leaching,resulting in spatial differences in soil hydrological properties and soil carbon,nitrogen and phosphorus,with strong spatial heterogeneity.The dry-hot valley area of Huajiang River in Guizhou is an experimental demonstration area of scientific and technological research projects since the Ninth Five-Year Plan period.It has accumulated more than 40 years of field observation data.In order to control the drought and soil degradation in the region,a series of economic crops such as pepper,loquat,pitaya and other plants with drought tolerance,light preference and calcium preference were introduced to control rocky desertification by returning farmland to forest and grassland.And to improve the local people ’s government income,improve people ’s lives.Therefore,this study selected the typical karst dry-hot valley area as the research area,and selected four different land use types(cultivated land,pepper forest land,pitaya land and loquat forest land)to measure soil hydrological properties and soil carbon,nitrogen and phosphorus.The spatial heterogeneity characteristics of soil water-fertilizer under different land use patterns were discussed in depth,and the spatial distribution pattern and influencing factors of soil water-fertilizer in karst rocky desertification area were revealed,in order to provide basic research data for future management and consolidation of the ecological environment in this area.The main research results are as follows :(1)The soil moisture content of cultivated land under four different land use patterns showed weak variation,and the other three plots showed moderate variation.The bulk density of loquat woodland was medium variation,and the other three plots were weak variation.The maximum water holding capacity of cultivated land and pitaya land was weak variation,while that of pepper woodland and loquat woodland was medium variation.The capillary water holding capacity of cultivated land,pepper forest land and pitaya land showed weak variation,and loquat forest land showed moderate variation.The capillary porosity and total porosity showed weak variation in the four plots.(2)The soil moisture content,capillary water holding capacity,capillary porosity and total porosity of cultivated land showed strong spatial autocorrelation.Capillary water holding capacity,capillary porosity and total porosity of Zanthoxylum bungeanum forest showed strong spatial autocorrelation.The bulk density,maximum water holding capacity,capillary water holding capacity,capillary porosity and total porosity of pitaya land and loquat land showed strong spatial autocorrelation.It shows that the spatial variation is mainly affected by the structural factors of natural conditions such as topography,altitude and climate.The bulk density and maximum water holding capacity of cultivated land are moderate spatial autocorrelation;the water content and maximum water holding capacity of Zanthoxylum bungeanum forest land are moderate spatial autocorrelation;the water content of pitaya land was moderate spatial autocorrelation,indicating that it was affected by both random factors caused by human activities such as fertilization,tillage methods and planting systems and structural factors.(3)The contents of SOC,TN and TP in pitaya soil were the lowest and the fertility was the worst under four different land use patterns.The content of SOC and TP in cultivated land was the highest,and the content of TN was second only to that of loquat forest land,and the comprehensive soil fertility was the best.From the perspective of coefficient of variation,SOC and TP in cultivated soil showed weak variation and had the distribution characteristics of homogeneous development,while the other three plots showed moderate variation.Soil TN showed weak variation.The C : N,C : P and N : P ratios of the cultivated land and loquat woodland showed weak variation,while the pepper woodland and pitaya woodland showed moderate variation.It shows that the stoichiometric characteristics of soil C,N and P in cultivated land and loquat forest land are more stable.(4)The nugget coefficients of SOC,TN and TP in pitaya land and loquat forest land were less than 25 %,showing strong spatial autocorrelation,which proved that they were greatly affected by natural factors such as altitude,climate and topography,while cultivated land and pepper forest land were affected by human activities to varying degrees.The soil C : N ratio of cultivated land and loquat forest land was moderate spatial autocorrelation,while that of pepper forest land and pitaya forest land was strong spatial autocorrelation.The soil C : P ratio of loquat forest was moderate spatial autocorrelation,and the other three plots were strong spatial autocorrelation.N : P ratio showed strong spatial autocorrelation.(5)There were significant differences in soil hydrological properties under four different land use patterns.There was a significant positive correlation between soil SOC and water content under different land use patterns.The contents of SOC and TP in cultivated soil were the highest,and the content of TN in loquat forest land was the highest.Among them,N deficiency became the limiting factor of cultivated land soil nutrients in southwest karst area,while P deficiency became the main limiting factor of pepper forest land,pitaya land and loquat forest land.