Study on the factor effecting erosion-resistance of calcareous soil in karst mountainous area——A case in the Shiqiao catchment of Bijie city,Guizhou province

It is showed by analysis to physic-chemical property of the calcareous soil in Shiqiao catchment that the sandy content in the soil decreases but the physical clayey content increases successively under the following land with different vegetation form,shrub and grass land,water and soil conservative forest and grass land,slope farmland.Those prove that the development of clayey grain in the soil on slope farmland is most serious.The hydro-stable aggregate content on shrub land is most,the size fraction of soil is largest and the soil water-stable is best.The organic content on shrub land is more and the size fraction of soil are larger,the soil hydro-stability is best.The organic content is more and soil structure is lower on shrub land.The soil dispersing rate on slope farmland,erosion ratio and eroded index is 1.11,1.14,1.04,1.13,1.87 and 1.82 times that on shrub land and water and soil conservative forest and grass land.The agglomeration degree and agglomeration status of cultivated land is 0.83,0.84,0.69,0.64 times that on shrub land and water and soil conservative forest and grass land,which shows that the dispersing rate on the slope farmland is maximum,the agglomeration degree on the slope farmland is the poorest and the soil anti-dispersion on the slope farmland is the weakest.The mean value of density and the capillary porosity of catchment,1.0 g/cm3 and 39.86%,are lower than that in the other region.The non-capillary porosity,averaged 25.88%,is lager than that in the other region in our country.This kind of combined characteristics of the calcareous soil pore in the catchment is easier leading to the clay at upper soil horizon to be leached downward and to block the pore at lower soil horizon,which causes saturated permeability different significantly between the upper and the lower soil layer,which is very unfavorable for the soil to resist running-water erosion.