Effect Of Orchard Natural Grass Technology On Soil Organic Carbon Pool In Loess Plateau

The Loess Plateau is recognized as an apple-producing area in the world,and the apple industry is the pillar industry to promote the economic development of this region and realize the strategy of rural revitalization.Grass growing in orchard is a kind of modern soil management measure which can improve soil quality in apple producing areas of Loess Plateau.According to grass growing methods,grass growing in orchard can be divided into artificial grass growing and natural grass growing.At present,artificial grass is the main grass growing in orchards,and the research on natural grass growing in orchards plays an important role in the optimization of grass growing model.Soil organic carbon is the core index of evaluating soil organic carbon pool.It is of great significance to explore the dynamic change of soil organic carbon pool for the evolution and quality improvement of orchard soil organic carbon pool.In this study,natural grass growing in apple orchard on Weibei Loess Plateau was taken as the research object,and clear cultivation and artificial grass were taken as the control.By analyzing soil organic carbon,active organic carbon components,stability of soil organic carbon pool,characteristics of dissolved organic matter（DOM）and soil physical and chemical properties,the interaction between stability of soil organic carbon pool,DOM characteristics,physical and chemical factors and other environmental factors was discussed.Thus,the improvement mechanism of soil organic carbon pool under natural grass in orchard was revealed,which provided theoretical support for the feasibility promotion of natural grass in the Loess Plateau.The main results of this study are as follows:（1）The soil organic carbon content and the quality of soil organic carbon pool were improved by grass mulching in orchard,and the influence on soil organic carbon pool was mainly in 0-40 cm soil layer.The improvement of soil organic carbon pool quality by natural grass was better than that by artificial grass.Natural grass had the best improvement effect on soil particle organic carbon,readily oxidizable carbon content and carbon distribution ratio,natural grass>natural grass rape>white clover>ryegrass.In the changes of soil total organic carbon,light fraction organic carbon,dissolved organic carbon and microbial biomass carbon,natural grass and natural grass rape treatment were higher than artificial grass ryegrass treatment,but lower than artificial grass white clover treatment,white clover>natural grass rape>natural grass>ryegrass.the microbial biomass carbon allocation ratio of natural grass rape treatment was the largest（1.35%）,while that of light fraction organic carbon（17.13%）and dissolved organic carbon（0.88%）allocation ratio of white clover treatment was the largest.（2）The soil DOM characteristics of 0-40 cm soil layer were mainly affected by grass cover in orchard.The improvement of humic acid component C1 and protein-like component C5 in natural grass treatment was higher than that in artificial grass treatment,the improvement of humic acid components（C2,C3）was lower than that of white clover treatment.Orchard grass reduced the protein-like component C4,and the surface soil was dominated by humic acid substances（56.91-67.56%）,while the deep soil was dominated by protein-like substances generated by microbial activities（52.85-57.71%）.The aroma degree of natural grass rape treatment was the highest（3.25）,which was higher than that of artificial grass treatment.But the proportion,humification degree and molecular weight of land plants were lower than that of white clover treatment.DOM characteristics of ryegrass treatment were lower.（3）Grass mulching in orchard improved soil physical and chemical properties mainly in0-40 cm soil layer.Natural grass treatment had the best improvement on soil physical properties,and natural grass rape treatment had the greatest increase on soil P and K,which was better than artificial grass treatment.The effect of natural grass and natural grass rape treatment on soil N was better than that of ryegrass treatment,but lower than that of white clover treatment.Soil physical and chemical driving factors had significant influence on DOM characteristics.Soil BD and p H were positively correlated with FI and SR,and negatively correlated with C1,C2,C3,C5 and HIX.Soil N,P and K nutrient factors were negatively correlated with FI and SR,and positively correlated with C1,C2,C3,C5,HIX and SUV₂₅₄.（4）Soil DOM characteristics and physicochemical factors had significant effects on the stability of soil organic carbon pool.The key factors affecting the stability of soil organic carbon pool were C3,C5,FI,AP,TN,AK and EC under natural grass treatment,and C5,FI,C3,AP,AK and NO₃^--N under natural grass rape treatment.White clover was treated with C5,HIX,FI,C2,AP,TN,NO₃^--N and AK,while ryegrass was treated with FI,C5,C1,AP and NO₃^--N.The main environmental driving factors of natural grass affecting the stability of soil organic carbon pool were soil physicochemistry.The artificial grass was DOM characteristic.In conclusion,natural grasses in orchards have positive effects on soil fertility and can effectively improve the quality of soil organic carbon pool.Compared with artificial grass,natural grass management saves time and effort,and can realize clean orchard production.Therefore,the popularization of natural grass in orchard in loess Plateau area is feasible.