Evaluation of the effects of long-term maize–peanut intercropping on soil aggregate stability based on different methods

Intercropping is an effective measure to increase crop yield and improve soil structure. The soil aggregate is the basic unit of soil structure, and its stability is affected by intercropping system. To study the effects of intercropping system on soil aggregate stability, the particle size distribution and stability characteristics of soil aggregates under three planting patterns of maize only (SM), peanut only (SP) and maize intercropped with peanut (M-P) were evaluated by dry sieving (mainly used to determine the mechanical stability of soil aggregates), wet sieving (mainly used to determine the water stability of soil aggregates) and Le Bissonnais (mainly used to distinguish different decomposition mechanisms of soil aggregates) (including slow wetting (SW), wet stirring (WS) and fast wetting (FW) tests) methods. The results showed that the particle size distribution of soil aggregates was mainly the >2 mm fraction in the dry sieving test, the 1–0.5 mm and <0.053 mm fractions in the wet sieving test, the >2 mm fraction in the SW test, the >2 mm and 2–1 mm fractions in the WS test and the 1–0.5 mm and 0.5–0.25 mm fractions in the FW test. The mean weight diameter (MWD), geometric mean diameter (GMD) and R_0.25 of soil aggregates in the three determination methods were all ranked as SP < SM < M-P, indicating that intercropping could increase the proportion of large aggregates and improve the stability of soil aggregates. In the three tests using the Le Bissonnais method, the MWD order was FW < WS < SW, indicating that the soil aggregates in this area were the most sensitive to slaking effects and the least sensitive to mechanical breakdown, and intercropping could reduce the sensitivity of soil aggregates to slaking effects and mechanical breakdown. In addition, the MWD of dry sieving was significantly positively correlated with the MWD of SW and WS, and the MWD of wet sieving was significantly positively correlated with the MWD of FW. The results of this study could provide a reference for better understanding of farmland soil structure and aggregate stability under intercropping system in the North China Plain.