Effects Of Land Use Types And Spatial Distribution On Soil Nutrients In The Karst Regions Of China

Composition and stability of soil organic matter(SOM)affect the sustenance and productivity of soil over the long-term.This issue is particularly important for karst regions in China where the water supply and fertilizer use are limiting factors.Small Karst catchments are common in Guizhou Province in China,where the soil nutrient supply is unique due to the porous soil parent.However,the spatial distribution of soil nutrients in the small Karst catchments in this province remains poorly understood.The soil is shallow and porous in these small Karst catchments.For typical Karst catchments in Guizhou,the land-use type,topography,and slope exert significant influences on the soil nutrients.Inspired by the first spatial distribution of soil nutrient in a typical Karst catchment,farmland to forests,while slope reclamation should be prohibited.Here,we used four indicators to evaluate changes in the composition and stability of SOM quantitatively in five main land-use types in karst area,including primary forest [PF],15-year secondary forest [SF],grazing secondary forest [GF],abandoned farmland [AF] and farmland[FL].Four indicators were used: soil physical and chemical properties,active organic carbon(C),humus C composition,and SOM functional groups.And we explored the spatial distribution of nutrients in a typical Karst catchment subject to three main land-use types(upper part of the slope: secondary forest [SF],middle part of slope: abandoned farmland [AF],and foot part of slope: farmland [FL]).A combination of total nutrients(soil organic matter[SOM],total nitrogen [TN],total phosphorus [TP],total potassium [TK])and active organic matter(easily oxidized organic carbon [EOC],water-soluble organic carbon [WSOC])soil nutrients were analyzed.The main objectives of this study were to: 1)systematically determine how different land-use types influence the content and composition of SOM using different indicators;and 2)comprehensively and quantitatively evaluate how different land-use types impact soil quality.3)determine the spatial distribution of long-and short-term nutrients,including the supply capacity in a typical karst catchment;4)reveal the factors that regulate the spatial patterns of soil nutrients in relation to various parameters,including slope,land-use type,vegetation biomass,soil texture,and microbial decomposition.Our findings are expected to help managers to determine rational land-use types for karst regions in China,which could be applied to enhance the sustainable development of fragile karst ecosystems in other areas globally.The results as below:In this study,our results showed that the content of SOM,total nitrogen,and easily oxidized organic C at 0–20 cm soil depth differed among the five landuse types(P < 0.05).Forhumic acid C concentration,the land-use types were ordered as: SF > PF > GF > FL > AF.Solid-state 13 C NMR spectra showed that the highest ratio of Alkyl C/O-alkyl C was in AF,while the lowest was in SF.Overall,the comprehensive quality of SOM in different land-use types was PF(setting 100%)> SF(83.1%)> GF(58%)> AF(30.9%)> FL(29.9%).In conclusion,our findings provide a scientific basis from which to delineate rational land-use types for different land(geographical and geological)formations.Soils in these small karst catchments are very sensitive to changes in land use and terrain features,due to their unique porous properties.We explored the spatial distribution of nutrients in a typical Karst catchment.The results showed that long-term soil nutrients at 0–10 cm and10–30 cm soil depths were generally the highest in the upper part of the slope and the lowest in the foot part of slope but were also higher on shady slopes compared to sunny slopes.The short-term soil nutrients in the 0–10 cm soil layer were highest in the upper part of the slope and lowest in the middle part of the slope.Inspired by the first spatial distribution of soil nutrient in a typical Karst catchment,farmland to forests,while slope reclamation should be prohibited.For typical Karst catchments in Guizhou,the land-use type,topography,and slope exert significant influences on the supply of long-term and short-term soil nutrients.In particular,information on both short-and long-term soil nutrient parameters in typical karst catchment areas could improve research on how to manage soil nutrients.