Response Of Spatial Differentiation Of Soil Properties To Vegetation Restoration In Consequent/Reverse Slopes Of Karst Trough Valley

In order to improve the ecological fragility and the difficulty of vegetation restoration in karst mountainous areas and balance the sustainable development of ecology,economy and society in Karst Mountainous areas,vegetation restoration is one of the important measures for ecological reconstruction in Karst areas.However,there is still some blindness in vegetation selection and later management.It is necessary to clarify the different vegetation restoration effects on soil properties under the special rock structure and soil environment.The effects of different vegetation restoration on the comprehensive quality of karst soil were discussed,and the limiting factors of karst soil fertility quality were found out.It can provide theoretical basis and scientific reference for ecological restoration and soil erosion/loss research in this area.It has important guiding significance for the selection of vegetation restoration and fertilization management in this area.In this study,Longtan trough valley in Youyang,Chongqing,was selected as the research area.Slopes with different rock strata in the trough valley?consequent and reverse slopes?and land with different vegetation restoration(forest land?LD?,pepper land?HJ?,shrub grassland?GC?were selected as the research objects.Soil samples were collected from 0-10cm,10-20cm and 20-30cm soil layers on the upper,middle and lower slopes,respectively.Based on field investigation and indoor test,the physical and chemical properties of the soil under three vegetation restoration on the consequent and reverse slopes in this area were analyzed,and the soil fertility quality was evaluated.The results show that:?1?Vegetation restoration can improve soil bulk density,water content and porosity percent,and soil infiltration effect is obvious,but there is no significant difference between the consequent slope and the reverse slope.Under the vegetation restoration modes on the consequent and reverse slopes,the bulk density of forest land is smaller than that of pepper land and shrub grassland,and the porosity and water content of forest land are higher than those of pepper land and shrub grassland.The infiltration rate of both forest land and pepper land began to decline slowly in about 30 minutes until it gradually stabilized after 75 minutes.The infiltration rate of shrub grassland reached stability in about 20 minutes.The infiltration performance was as follows:forest land>pepper land>shrub grassland?P<0.05?.Compared with Kostiakov and Philip models,Horton model is the best model for fitting soil infiltration process under different vegetation restoration in this area,R² is 0.9789.The factors affecting soil infiltration in this area are:total porosity>non-capillary porosity>saturated water content>pH>organic matter.The multiple linear regression model based on the above factors with 95%confidence can accurately predict the stable infiltration rate of soil in this area,which has certain application value.?2?The characteristics of soil microaggregates differ significantly between the consequent and reverse slopes and different vegetation types.The dominant particle size of soil microaggregates on the consequent and reverse slopes are 1-0.25 mm,0.05-0.01 mm,and the fractal dimension?D?of soil is 2.62-2.64 and 2.64-2.66,respectively.The structure stability of soil microaggregates on the consequent slope is better than that on the reverse slope.The fractal dimension D of soil microaggregates was GC>LD>HJ in the consequent slope and HJ>GC>LD in the reverse slope.S-HJ and N-LD soil had better microaggregate structure.1-0.05mm particle size distribution was"V"on S-LD slope and"L"on S-HJ and S-GC slope,while it decreased with the decrease of slope position under the restoration of three vegetation types on reverse slope,decreased with the increase of soil depth on forest land of consequent and reverse slope,and increased with the increase of soil depth on pepper land and shrub grassland.The fractal dimension D of soil microaggregates fitted better with the diameter of<0.001 mm microaggregates?R²=0.974?and worse with the diameter of0.05-0.01 mm.It was negatively correlated with the diameter of 1-0.25 mm particles,silt particles,TK and organic matter,and positively correlated with the diameter of<0.001 mm,0.005-0.001 mm and MWWSA?P<0.05?.The results are helpful to establish the relationship model between the fractal dimension of soil microaggregates and the physical and chemical properties of soil in this area.?3?The difference of soil chemical properties between slope type and vegetation type is obvious.Soil pH was consequent slope?5.99?<reverse slope?6.56?.Soil in pepper land tended to acidify,and pH?5.48?was the lowest.Soil pH had little difference between forest land and shrub grassland slope,while that of pepper land slope was upper slope>middle slope>lower slope,and increased with the increase of soil layer.The contents of soil organic matter,TN,TK and AP were consequent slope>reverse slope,while the contents of TP,NH₄⁺-N,NO₃^--N and AK were consequent slope<reverse slope.Soil organic matter content in both consequent and reverse slope were LD>HJ>GC?P<0.05?;soil TP content was the highest in pepper land,and S-HJ>S-GC>S-LD,N-HJ>N-LD>N-GC;TN content was S-HJ>S-LD>S-GC,N-LD>N-HJ>N-GC;TK content was S-GC>S-HJ>S-LD,N-HJ>N-LD>N-GC.The contents of NH₄⁺-N,NO₃^--N,AP and AK in soil under three vegetation restoration were significantly different?P<0.05?.Under the influence of artificial fertilization,the available nutrients of pepper land in the consequent and reverse slopes were significantly higher than those in the forest land and shrub grassland.?4?The content of soil organic matter and nutrients did't increase with the decrease of slope position under different vegetation restoration in this area,but there was obvious accumulation in the profile.Karst rocks and grooves hinder the movement of soil on slopes.The contents of soil organic matter,TN,TP?except S-GC?and TK?except S-HJ?accumulate from upper to middle or lower slopes,but do not increase with the decrease of slope position.The content of soil organic matter,TN and available nutrients decreased with the increase of soil depth in different vegetation restoration on the consequent and reverse slopes?P<0.05?.The content of TP and TK in the consequent slope decreases first and then increases with the increase of soil depth.The content of TP in the reverse slope decreases with the increase of soil depth,and the content of TK in the soil increases with the increase of soil depth.According to the coefficient of surface aggregation,except that soil TK did't follow the law of surface aggregation,other nutrient indicators had obvious characteristics of surface aggregation,among which AP had the strongest surface aggregation and shrub grassland had the weakest surface aggregation.?5?Soil nutrient indicators in this area are less affected by soil pH and sand content,and soil available nutrient content is mainly affected by soil phosphorus and clay content.Soil TN and TK contents are significantly positively correlated with soil organic matter and silt content.The soil fertility quality of different vegetation restoration models in this areais N-GC?0.0762?>N-HJ?0.0248?>N-LD?0.019?>S-GC?-0.0038?>S-HJ?-0.0324?>S-LD?-0.0838?.That is to say,the soil fertility quality of the reverse slope is better than that of the consequent slope,and that of the shrub grassland is better than that of pepper land and forest land.Therefore,a single physical and chemical index can't characterize the quality of soil.In conclusion,shrub and grass restoration is the best transition mode to improve soil fertility quality in this area,and more attention should be paid to soil and water conservation of consequent slope.