Difference Of Physical Properties Of Soil Profiles Under Different Vegetations In Karst Mountainous Area

Based on the method of field sampling and indoor analysis,the differences of soil physical properties under different vegetation in karst mountainous area were studied.Soil samples of six vegetation types were collected in Typical Rocky Desertification Area of Qinglong County,Guizhou Province,including Crop.Forage grass.Weed vegetationand Shrubbery Intercropping vegetation and forest.their physical properties indexes were measured,and the physical indexes of soil profile were analyzed Based on the difference,the key indexes of soil physical properties driven by vegetation restoration were screened,and the comprehensive index of soil physical quality was used to evaluate the impact of vegetation restoration on soil physical properties.The main conclusions are as follows:(1)In the karst rocky desertification area as a whole,the change trend of soil particle sand content decreases with the depth of the soil layer,and the clay content increases with the depth of the soil layer;the content of soil micro-aggregates increases with the soil layer depth.The content of small-sized micro-aggregates gradually increases as the depth of the soil layer deepens;the content of water-stable aggregates in the soil >5mm in the middle and surface layers is greater than that in the deep layer,and the content of small-sized micro-aggregates increases with the increase in soil depth.The overall trend is decreasing.(2)The soil structure characteristics of the karst rocky desertification area showed that MWD,MWSSA,agglomeration status,and degree of agglomeration decreased with the increase of soil layer,indicating that the stability of soil structure became weaker as the soil layer deepened,and the corrosion resistance became worse.The soil fractal dimension and soil density gradually increase with the increase of soil depth,indicating that as the soil layer deepens,the stability of the soil structure becomes worse.On the whole,the physical properties of the underground soil in various vegetation samples have vertical changes in this study.The more developed the soil,the better the physical properties.(3)In karst mountainous areas,with the restoration of vegetation,soil bulk density under various vegetation types decreased,and natural moisture content,field water holding capacity,total porosity,capillary porosity and non-capillary porosity increased.The content of coarse-grained micro-aggregates and agglomerates increased,while the content of fine-grained micro-aggregates and agglomerates decreased,but the composition of soil particles was that the content of coarse-grained soil particles decreased and the content of fine-grained soil increased.It shows that with the continuous restoration of rocky desertification ecology,the soil structure has gradually improved.(4)The soil MWD and MWSS of all vegetation types in the karst mountainous areas were larger than crops after the vegetation was restored from farmland,and the grass cover reached the highest value.The reunion status and degree of reunion reached the highest value under forest and grass cover,and the lowest value under crops.The crops have the highest soil density and the worst air permeability,while the grass covers have relatively low soil density and better air permeability.It shows that the structure of weed quilt,forest and grass quilt is relatively stable,and crops are the weakest(5)Correlation analysis of various physical indicators of the soil shows that most physical indicators have different degrees of correlation;the physical properties of the study area are mainly affected by the composition and structural characteristics of soil micro-aggregates,and the comprehensive physical qualityindex of weeds is the highest,The physical quality of soil is the best;compared with crops,the physical quality of soil in karst rocky desertification areas has gradually improved with ecological restoration after the conversion of farmland.The above research results can provide a scientific basis for the improvement of soil quality and vegetation construction in karst rocky desertification areas,and a theoretical basis for further optimization of vegetation type configuration.In the process of ecological restoration and rock desertification control in Karst region,it is recommended to shorten the time for returning farmland through artificial control measures and accelerate the increase of vegetation coverage such as multiple rhizosphere plants to effectively reduce soil erosion and improve the ecological environment of the area.