Differences In Soil Physical And Chemical Properties In Different Karst Habitats And Their Spatial Differentiation Characteristics

The karst ecosystem in southwest China is characterized by serious rocky desertification,shallow soil layer and poor water and fertilizer conservation ability.How to improve soil physical properties and soil nutrients is a difficult problem to improve the ecological environment in karst areas.Due to the influence of bedrock outcrop,microtopography and other factors,the spatial heterogeneity of soil physical and chemical properties is large in karst ecosystem.Understanding the difference of soil physical and chemical properties in different habitats and the influence of exposed bedrock on the spatial difference of soil physical and chemical properties in karst areas will be helpful for further understanding the soil physical and chemical properties in karst areas,and provide reference for rational land planning and sustainable development of productivity in karst ecologically fragile areas.Four quadrats(10 m×l0 m)were set up in typical karst QG and GC under high bare rock ratio(HRR)and low bare rock ratio(LRR)habitats in Guangxi.Grids were set up in each quadrat according to 1 m× L m.The physical and chemical properties of soil(BD,Ks),soil mechanical composition,soil aggregates,porosity,soil organic matter(OM),soil total nitrogen(TN),soil total phosphorus(TP),and soil total potassium(TK)at the surface layer(0-10 cm)of each grid vertex were collected and measured.The differences and spatial distribution characteristics of soil physical and chemical properties under different habitats and vegetation types were analyzed,and the effects of exposed bedrock on soil physical and chemical properties were discussed.Through experiments and analysis,the main conclusions of this study are as follows:(1)The soil texture in the study area is sandy loam to clay loam.According to the difference of soil bulk density,porosity and saturated water conductivity in different habitats,the soil under the high bare rock ratio under the qiao irrigation type is loose,with high porosity and strong permeability,and it is not easy to produce surface runoff.In terms of soil aggregate content and aggregate structure,soil aggregate degree was higher and soil stability was better under irrigation.Soil moisture content(SMC)of all types of plots in rainy season was higher than that in dry season.SMC had the most obvious response to rainfall under high bare rock ratio irrigation,and its increase was the largest after rainy season and decrease was the largest in dry season.(2)The contents of soil organic matter and nutrients were the highest in the high bare rock ratio and the soil nutrients showed moderate variation in each type.The results of soil C,N,P ratio showed that high bare rock ratio irrigation was beneficial to THE retention of C.The results of soil C:P showed low availability of SOIL P,which was not conducive to plant growth.Soil N:P ratio was lower than the national average.The soil nutrient limiting factor in the study area was N,and the soil nutrient availability was low.(3)In this study,the index model is the best model for fitting soil physical and chemical properties,and its determination coefficient is >0.78,which can better simulate the spatial structure of various physical and chemical properties.The results of block to base ratio showed that BD and Ks showed moderate spatial autocorrelation,and soil nutrients showed moderate to strong spatial autocorrelation.The variation range of soil physical properties(BD and Ks)was small(1.39 m ? 3.74 m and 2.45 m ? 6.17 m,respectively),while the variation range of soil chemical properties(OM,TN,TP and TK)was large,and some nutrient variation ranges exceeded the sampling range,indicating that the sample plot needs to be further expanded.(4)The physical and chemical properties of soil are significantly correlated with each other,and their spatial distribution is closely related to the outcrop bedrock.Except BD,which has a low value and is distributed around the outcrop bedrock,the other physical and chemical properties show high values and are distributed around the outcrop bedrock.Soil Ks,SMC,OM,TN,TP and TK decreased with the increase of the distance from exposed bedrock in rainy season,while BD and SMC increased with the increase of the distance from exposed bedrock in dry season,indicating that the physical properties of soil were more affected by exposed bedrock.