Changes And Influencing Factors Of Structural Stability Of Typical Loess Soil Aggregates

Aggregate stability is an important soil physical property that determines soil erosion resistance and degradation ability.The Loess Plateau has high soil erosion intensity and extensive soil erosion area.The research on soil aggregate stability in this area is mostly based on water-stable aggregates.There are few studies on changes in aggregate structural stability.In order to find out the main factors affecting the structural stability of typical loess soil aggregates,this study took the Zhifanggou watershed and the Ziwuling forest area as the research area,and selected soils with different land uses and different vegetation succession stages as the research areas.The differences in soil physical and chemical properties,aggregate structural stability and soil erodibility between different land uses,vegetation succession stages and soil depths were analyzed.The variation characteristics of soil aggregate structure stability in different land uses and vegetation succession stages and the effects of soil physical and chemical properties on the aggregate structure stability were clarified.The main physical and chemical factors affecting the of aggregate structural stability were revealed,which can stabilize soil structure and improve soil quality in loess hilly areas,enhance soil corrosion resistance and provide a basis and theoretical basis for soil erosion control.The main results are as follows:（1）The composition of soil effective particle size in different land uses is mainly composed of silt-grade particles,followed by sand-grade particles,and clay-grade particles are the least;in different vegetation succession stages,sand-grade particles are mainly,followed by silt-grade particles,with the least amount of clay-grade particles.The soil texture classification of the two study areas is silt loam.The p H values of the upper and lower soil layers were between 8.65-8.85 and 8.71-8.98 in different land uses,respectively,and the p H values of the soils in different vegetation succession stages were between 8.16-8.50 and 8.40-8.64,respectively,indicating that the soil was alkaline.The electrical conductivity of the upper and lower soil layers in different land uses is between 0.144-0.177 d S m^-1,0.138-0.170 d S m^-1,respectively,and the soil conductivity values in different vegetation succession stages are0.165-0.207 d S m^-1,0.154～0.189 d S m^-1,all between 0～2 d S m^-1,indicating that the soil does not contain salt.The p H,clay,silt and CaCO₃ contents of forest and grassland were lower than those of agricultural land,while the content of sand,electrical conductivity,SOC and TN were significantly higher than those of agricultural land.The cation exchange capacity and exchangeable cation content of soil under different land uses were less different.The water stability of the aggregates in the 0-15 cm soil is the strongest in the grassland,and the other land uses have little difference.The 15-30 cm soil is significantly higher than that of the forest and grassland.The cation exchange capacity of soil in different vegetation succession stages increased continuously with the forward succession process,while the content of exchangeable cations showed little difference.The water stability of the aggregates was significantly higher than that of the farmland,among which the 0-15 cm soil Sea buckthorn was the most stable,and the 15-30 cm soil Quercus Liaodong was the most stable.With the deepening of soil depth,there was no significant change in soil particle size composition,electrical conductivity,p H of farmland,and water stability of aggregates in different land uses and vegetation succession stages,SOC,TN content and water stability of forest-grass aggregates decreased significantly,while soil Ca CO₃content and forest-grass p H increased significantly.（2）The S_iR values of the aggregate structure stability index of millet,potato,corn,orchard,abandoned land,grassland and locust in 0-15 cm soil were 0.74,0.71,0.70,0.75,0.76,0.85 and 0.86,respectively.The overall performance is grassland and locust>abandoned land>orchard>millet>potato and corn.The S_iR values of 15-30 cm soil aggregates were 0.62,0.64,0.61,0.59,0.63,0.73 and 0.78,respectively,showing the order of locust>grassland>potato>abandoned land>millet>corn>orchard.The structural stability of soil aggregates in the upper and lower layers of each land use was significantly higher in 0-15 cm than in 15-30 cm.The SR values of the aggregate structural stability index in 0-15 cm soil of farmland,grassland,sea buckthorn,aspen and Liaodong oak were 0.46,0.43,0.49,0.59 and 0.70,respectively.The overall performance is Liaodong oak>aspen>sea buckthorn>farmland>grassland.The SR values of 15-30 cm soil aggregates were 0.36,0.46,0.65,0.68 and 0.52,respectively,showing the order of aspen>sea buckthorn>Liaodong oak>grassland>farmland.Among them,the structural stability of soil aggregates at 0-15 cm in farmland and Liaodong oak was significantly higher than that at 15-30 cm,while that in grassland,sea buckthorn and aspen was the opposite.（3）The erodibility factors（K） of 0-15 cm and 15-30 cm soils under different land uses were between 0.2218～0.2248 and 0.2214～0.2265,respectively,and the differences among different land uses were small.The K values of the upper and lower soils in different vegetation succession stages ranged from 0.1647 to 0.1902 and 0.2045 to 0.2225,respectively.The K value of soil in each vegetation succession stage was significantly lower than that of farmland.The K value of the subsoil was higher than that of the topsoil in different land uses and vegetation succession stages.（4）The results of redundancy analysis showed that clay-grade particles,electrical conductivity,sand-grade particles,SOC,TN,sand and p H were the main factors affecting the structural stability of soil aggregates in different land uses（P<0.05）.Among them,clay-grade particles and p H showed a negative effect,while conductivity,sand-grade particles,SOC,TN and sand showed a positive effect.Clay-grade particles accounted for 48.0%of the aggregate structural stability,which was the most important factor affecting the soil aggregate structural stability in different land uses.The silt-grade particles,Ca CO₃,p H,water stability of aggregates,SOC were the main factors affecting the structural stability of soil aggregates in different vegetation succession（P<0.05）.Among them,silt-grade particles,Ca CO₃ and p H showed a negative effect,while aggregate water stability and SOC showed a positive effect.The silt-grade particles accounted for 76.1%of the structural stability of aggregates,which was the most important factor affecting the structural stability of soil aggregates in different vegetation succession.