Study on the structure and stability characteristics of typical black soil aggregates in Northeast China based on Le Bissonnais method

Abstract :[Background] The black soil area in northeast China is an important grain production base in China, and soil erosion is serious. Soil aggregate stability has a profound influence on soil erosion process. The purpose of this study was to clarify the fragmentation characteristics of surface and bottom soil aggregates in sloping farmland under different damage mechanisms, and to evaluate the stability characteristics of aggregates under different damage mechanisms, so as to provide theoretical basis for the prevention and control of soil erosion in sloping farmland in rainy season. [Methods] The typical long straight sloping farmland in northeast Black soil region was selected as the study area. Samples were taken every 30 m along the longitudinal section of the slope length, with a sampling depth of 30 cm and a sampling length of 1020 m. The particle size distribution and stability parameters of soil aggregates were determined by Le Bissonnais (LB) method (including fast wetting (FW), slow wetting (SW) and runoff disturbance (WS) treatments. [Results] 1) Under the three treatments of LB method, FW treatment (rainstorm) had the largest damage to soil aggregate structure, SW treatment (light rain) had the least damage to soil aggregate structure, and WS treatment (disturbance) was in the middle. On the whole, the aggregate stability showed MWD_SW>MWD_WS>MWD_FW. 2) Analysis of soil aggregates in the topsoil (0-10 cm) showed that SW treatment (light rain) caused the soil aggregates to break into aggregates of >0.2 mm. WS treatment (disturbance) caused the fragmentation of soil aggregates mainly concentrated in 2-0.2 mm grain size, indicating that the >2 mm grain size aggregates were mainly destroyed by raindrop splashing, which made them split into microaggregates. After FW treatment (rainstorm), the aggregates were broken in <1 mm size, which provided abundant loose aggregates for raindrop splash erosion and runoff erosion process, and became the main source of erosion materials in soil erosion process. 3) The aggregate fragmentation of surface layer (0-30 cm) was more sensitive to 0-10 cm soil layer after light rain. The aggregate fragmentation effect under rainstorm and irrigation was more obvious in 0-20 cm soil layer. The effects of raindrop splashing and runoff disturbance on aggregate fragmentation in 0-30 cm soil layer are similar. MWD_0-10cm < MWD_10-20cm < MWD_20-30cm in different soil layers under the three failure mechanisms. 4) In the three treatments of LB method, 1 mm grain size was taken as the critical, and 1 mm grain size was used as the index to distinguish soil stability. Soil aggregate size >1 mm had a strong resistance to soil dissipation, clay expansion and mechanical oscillation. This result could characterize the factors affecting soil stability structure.