Effects Of Different Grazing Intensities On Soil Aggregate Stability In Typical Steppe

Grassland soil protection and degraded soil remediation are important research fields of environmental engineering in arid and semi-arid regions,and also one of the important contents of ecological safety barrier construction in northern China.Soil aggregates are important indicators to characterize soil structure and stability,which have attracted extensive attention in ecology,agricultural science and environmental science in recent years.Soil aggregates and their stability are important driving factors affecting soil fertility and soil carbon storage,and they are extremely sensitive to land use intensity.At present,the studies on the effects of grazing on grassland soil aggregates mostly focus on the relationship between soil physical and chemical properties and aggregates,and there are few studies on the effects of grazing disturbance on soil aggregates and their stability.In this study,the typical steppe in Xilingol League of Inner Mongolia was taken as an example,and four grazing intensives were set up on the grazing experimental platform: control(0 sheep/day·hm2),light grazing(2 sheep/day ·hm2),moderate grazing(4 sheep/day ·hm2)and heavy grazing(8 sheep/day ·hm2).The underground biomass,soil physicochemical properties,soil microbial biomass and the grain size distribution of soil aggregates under different grazing intensities were measured,and the effects of underground biomass,soil physicochemical properties and soil microorganisms on the content and stability of soil aggregates under different grazing intensities were analyzed.The results of this study can provide basic data for the study of the mechanism and process of soil aggregate structure and stability change in grassland ecosystem,and also provide reference for grassland soil protection and remediation of degraded soil.The important findings and conclusions are as follows:1.In the 0-40 cm soil layer of typical steppe,the underground biomass,soil total carbon,total nitrogen,organic carbon and microbial biomass nitrogen decreased significantly with the increase of grazing intensity and soil depth,but the soil bulk density and microbial biomass carbon contents increased significantly.2.With the soil depth deepening,soil mechanical stability of large aggregates(dry screen)(>0.25mm),resulting in large water-stable aggregates(wet screen)(>0.25mm);The content of >7mm size size mechanically stable large aggregates and >2mm size size water stable large aggregates increases with the increase of grazing intensity.In the soil layer below 10 cm,the content of the two large aggregates showed the order of heavy grazing>control>light grazing>medium grazing,and only the middle grazing was significantly reduced compared with the control.3.The average weight diameter(MWD)and geometric mean diameter(GMD)of the aggregates of mechanical stability and water stability between 0-10 cm increase with the increase of grazing intensity.But below 10 cm,the MWD and GMD of the two aggregates under the light grazing and middle grazing treatments gradually decreased,and at the same time their fractal dimension D and soil erodibility factor K began to be higher than the control.Under heavy grazing treatment,the aggregate MWD and GMD were higher than those of the control,and the D and K values gradually decreased.At this time,the aggregate stability showed as heavy grazing>control>light grazing>moderate grazing.Heavy grazing improves the stability of soil aggregates,while light grazing and medium grazing reduce the stability of aggregates.4.Grazing has an indirect impact on soil organic carbon and microbial biomass by directly affecting soil bulk density and underground biomass.At the same time,soil bulk density and underground biomass have a direct or indirect impact on the stability of aggregates,and combined with the direct impact of soil organic carbon and microbial biomass to affect changes in soil stability.The results of this paper show that higher grazing pressure is beneficial to increase the content of soil macroaggregates,thereby improving soil mechanical stability and water stability,and enhancing soil erosion resistance.