Study On Stability Of Soil Aggregates And Its Influencing Factors Under Vegetation Restoration Of Artificial Forest And Grass In Rocky Desertification Area

Soil aggregate stability and its influencing factors under different vegetation restoration models is great significance for the evaluation of soil restoration effect,as well as the prevention of rocky desertification.Six sample plots were set up on lands of typical rocky desertification area soil with different vegetation restoration models(Walnut,Rosa roxburghii Tratt,Ryegrass,Walnut-Rosa roxburghii Tratt,Rosa roxburghii Tratt-Ryegrass,Walnut-Ryegrass)located in salaxi rocky desertification comprehensive control area,Bijie City,Guizhou Province of China.The cultivated land(Corn)was selected as control.Including the content and its stability of different aggregate fractions within 0-20cm soil layer were analyzed by drying and wetting experiment.The effects of different vegetation restoration models on the evolution of aggregate structure were analyzed,which based on the physical and chemical properties properties,stoichiometric characteristics,soil enzyme activities and aggregate nutrients.The main conclusions are as follows:(1)There were significant differences in the distribution of aggregates between the six kinds of forest grassland and agricultural land.Dry sieving within 0-20cm soil layer test showed that the aggregates content with particle size of>2mm is highest,followed by 0.25-2mm,The variation ranges were 41.30-72.38%and 22.96-42.28%respectively;Wet sieving analysis showed that the dominant particle size of aggregates changed to 0.25-2 and 0.053-0.25mm.After the farmland was changed into different forests and grasslands,the content of large aggregates,the aggregate diameter(MWD,GMD)and stability coefficient(ASI)increased,while the structure failure rate(PAD),erodibility(K)and fractal dimension(D)decreased.The content of large aggregates increased after the farmland was changed into different forests and grasslands.It shows that the vegetation recovery modes of artificial forest and grass is beneficial to improve the stability of aggregates.The MWD,GMD and ASI of underground aggregates in walnut and walnut Rosa roxburghii Tratt were higher than those in other forests and grasslands,and the PAD,K and D were lower,The effect of walnut single planting and walnut Rosa roxburghii Tratt mixed planting was the best.Correlation analysis shows that 0.25mm and 2 mm particle size are important critical points in the process of soil particle agglomeration.(2)Compared with traditional farmland,soil BD of different forests and grasslands decreased.The porosity and saturated hydraulic conductivity increased.The content of SOM,N and P in the vegetation recovery modes of artificial forest and grass is increased,which most of them belonged to medium variability.RDA analysis showed that the stability coefficient and aggregate diameter were positively correlated with SOM,AN,K_S,AP,p H,TN and TP,respectively.It was negatively correlated with MC,FWR,BD and sand.SOM,AN and KS play a good role in explaining the variation of aggregate stability.(3)The activities of soil urease,sucrase and acid phosphatase in the vegetation recovery modes of artificial forest and grass is increased significantly.It is consistent with the change trend of soil C and N.The content of carbon and nitrogen in aggregates increased during the process of particle size change from>2mm to<0.053mm.Its enrichment state gradually changed from preferential decomposition to preferential accumulation.while the change rule of phosphorus enrichment state was poor.Aggregate particle size of<2 mm play a major role in soil nutrients.In general,the maximum of C/N,C/P and N/P of aggregates is the particle size of 0.25-2 and0.053-0.25mm,respectively.The result of correlation analysis showed that C in the aggregate has a great influence on C/N,while N/P was mainly affected by N.Redundancy analysis showed that the activities of phosphatase and sucrase,C/N,C/P played an important role in the change of soil aggregate structure in the vegetation recovery modes of artificial forest and grass.The results shows that the vegetation recovery modes of artificial forest and grass is beneficial to improve the stability of aggregates.The effect of walnut single planting and walnut Rosa roxburghii Tratt mixed planting on improving soil structure is the best.It is suitable for implementation and promotion in the radiation range of the study area.This study provides a reference for the selection and optimization of vegetation restoration model for rocky desertification control.The effects of plant,microorganism and soil animal on the stability of soil aggregates in the process of vegetation restoration in rocky desertification area remaind to be further study.