Variation Characteristics Of Soil Aggregates And Aggregate Carbon In Orchards Covered With Living Mulching

Soil aggregate is the basic unit of soil structure,and its organic and inorganic cementation and adsorption have certain physical protection effect on organic carbon（SOC）content.In addition,SOC can also promote the formation and stability of soil aggregates.Therefore,soil quality and fertility are directly affected by the quantity and quality of aggregates and can be used as indicators for monitoring soil quality in the process of land use and management.In this study,the apple orchard in the Loess Plateau was selected as the research field,and the traditional management clean tillage was used as the control.The content of mechanical stability aggravates,water stability agglomerates and micro-agglomerates was measured by dry sieve method,wet sieve method and filtration method,respectively.The treatment included2,5,8 and 12-year of white clover,crown vetch and the orchard grass of 12-year.The organic carbon content of soil aggravates was measured by K₂Cr₂O₇ volume method.The characteristics of content,stability and evolution of organic carbon of aggravates were based on different years and grass species.The aim is to indicate the response and feedback effect of organic carbon soil aggravates and aggravates carbon on orchard grass management in orchard.Further promote the theory and speed up the popularization of the technique of orchard grass management.Finally,in order to improve the soil quality of orchards,to achieve sustainable quality and high yield of orchards to provide advance suggestions.The mainly findings are as follows:（1）In the study area,water stability aggravates were the main number of soil aggregates,and the effect of grass mulching on the particle size composition and stability of soil aggravates was more accurately reflected by wet sieve method than dry sieve method.After the mulching of grass,the content of aggravates in orchard soil increased obviously,and the stability improved well.The content of the aggravates of the soil particle size>0.25 mm particle size increases,the Mean weight diameter value increases significantly,and the Destruction rate and Fractal dimension value decrease significantly.Moreover,with the increase of the number of years of grass mulching,the stability of orchard soil aggravate content increased more and more,and the improvement of the stability of soil aggravates in different grass species mulched the greatest effect of white clover,the second in crown vetch and the orchard grass.（2）In the soil layer of 0-40 cm,the soil organic carbon content showed a decreasing trend with the increase of soil depth.In each soil layer,the organic carbon content of 0.25-0.5mm particle size was larger than that of other particle size（p<0.05）.And with the increase of the number of years of grass mulching,the organic carbon content of orchard soil aggravate increased gradually.The increase of organic carbon content of different grass species to soil aggregates showed that the white clover were the most effective,the crown vetch were the second,and the orchard grass was the smallest.（3）The contribution rate of organic carbon content of aggregates with 0.25 mm particle size to soil organic carbon content was significantly higher than that of<0.25 mm particle size aggregates to soil organic carbon.Among them,the organic carbon content of the aggregate of 0.25-0.5 mm particle size contributes higher to the soil organic carbon content of the soil layer than other particle sizes.The three treatment increased the contribution rate of aggregate organic carbon of 0-20 cm soil>0.25mm particle size to soil total organic carbon（p<0.05）.The greater the depth of the soil layer,the physical protection of soil organic carbon by the aggregates with a particle size of>0.25 mm is gradually weakened,and the physical protection of the micro-aggregates（<0.25 mm）on soil organic carbon is more prominent.