Response Of Soil Physical Properties To Grassland Degradation In Typical Steppe

As an important ecological barrier in northern China,most of the typical grasslands have been degraded to different degrees.Soil structure is the basis of soil function,and long-term grassland degradation will cause soil physical changes.In order to clarify the response of soil physical properties with different textures to grassland degradation and analyze the optimal response indexes,Taking the typical grassland in Saihanwula region of Chifeng City,Inner Mongolia as the study area,Three kinds of soils with different textures(sandy soil,sandy loam and loam)and grassland with different degrees of degradation were selected as the research objects.Correlation analysis of soil saturated water conductivity,bulk density,total porosity,gravel and mechanical composition was conducted to reveal the response of soil physical changes with different textures to grassland degradation.The analysis results are as follows:1.The analysis of the change law of the main physical indexes of sandy soil surface with the intensification of grassland degradation showed that the indexes of saturated water conductivity,bulk density and clay increased,the indexes of porosity and sand decreased,the indexes of silt increased first and then decreased,and the indexes of gravel decreased first and then increased.The analysis of the change law of the main physical indexes of the underlying soil showed that gravel showed an upward trend,saturated water conductivity,bulk density,sand index showed an upward trend and then a downward trend,and porosity,silt and clay index showed a downward trend and then an upward trend.The indicators of sandy surface soil and grassland degradation were significantly correlated,including saturated water conductivity(r=0.4616),bulk density(r=0.8960),total porosity(r=0.7470),sand(r=0.9894)and clay(r=0.9473).The indicators of sandy subsoil significantly correlated with grassland degradation included gravel(r=0.8060),sand(r=0.5714)and silt(r=0.6252).2.The analysis of the change law of the main physical indexes of the sandy loam surface soil with the intensification of grassland degradation showed that the sand index increased,the silt and clay index decreased,the saturated water conductivity and bulk density index increased first and then decreased,and the porosity and gravel index decreased first and then increased.The analysis of the change law of the main physical indexes of the lower soil showed that the bulk density and sand index increased,the porosity index decreased,the saturated water conductivity and clay index increased first and then decreased,and the gravel and silt index decreased first and then increased.Sand(r=0.9894),silt(r=0.8881)and clay(r=0.7979)were significantly correlated with grassland degradation in sandy loam surface soil.The indexes of sandy loam subsoil were significantly correlated with grassland degradation,including bulk density(r=0.7030),total porosity(r=0.7089),sand(r=0.8705),silt(r=0.8705)and clay(r=0.6649).3.The analysis of the change law of the main physical indexes of loam surface soil with the intensification of grassland degradation showed that the sand index decreased,the saturated water conductivity,porosity and indexes increased first and then decreased,and the bulk density,gravel,silt and clay indexes decreased first and then increased.The analysis of the change law of the main physical indexes of the underlying soil shows that the saturated water conductivity presents an upward trend,the silt particle index presents a downward trend,the porosity and sand particle index presents a downward trend,and the bulk density,gravel and clay particle index presents a downward trend.The indexes of loam surface soil were significantly correlated with grassland degradation,including porosity(r=0.4600),sand(r=0.9828)and clay(r=0.7451).The indexes of loam bottom soil were significantly correlated with grassland degradation,including saturated water conductivity(r=0.4290),total porosity(r=0.5532),silt(r=0.8297)and clay(r=0.7322).4.With the increase of grassland degradation,the main surface soil physical indexes of the three germplasm plots tended to be the same as the gravel index,while the change trends of the other indexes were inconsistent.The changes of main physical indexes of grasslands with different textures in the underlying soil were not consistent.The comparative analysis of soils with different textures showed that sand and clay were significantly correlated with grassland degradation in the topsoil,while silt and sand were significantly correlated with grassland degradation in the subsoil(P<0.05).Based on the changes and correlations,the main physical optimum index of the surface soil is sand,and the bottom soil is silty sand.