Interspecific interactions increase soil aggregate stability through altered root traits in long-term legume/maize intercropping

Species-diverse intercropping systems are associated with increases in soil aggregation but the underlying root mechanisms responsible for greater soil aggregation remain poorly understood. A three-year-long field study was conducted comprising two nitrogen (N) and phosphorus (P) application rates (with and without N or P), and five cropping systems: two maize-based intercropping systems (with peanut or soybean) and their corresponding monocultures (peanut, soybean and maize). Water-stable aggregates and six crop root traits were measured in both monoculture and intercropping. At the plot scale the percentage of soil macroaggregates (R 0.25 ), mean weight diameter (MWD), root length density (RLD), biomass density (RMD), volume (RV), and total surface area (RS) had significantly higher values in legume/maize intercropping and maize monoculture than in legume monoculture. At the field-strip scale, intercropping increased the R 0.25 and MWD of legume strips by 6.4–13.3 % and 13.9–31.9 % compared to the corresponding legume monocultures. This was induced by the synergistic effects of maize root residues from the previous growing season and the spatial extension of maize roots in the current growing season. Maize roots affected the soil aggregate stability of neighboring soybean and peanut strips in different ways. Intercropping promoted soil aggregation of neighboring soybean strips mainly via maize root traits within the growing season. In contrast, intercropping promoted soil aggregation of the same peanut strips mainly via pre-maize root traits. The results indicate that intercropping can promote soil aggregation, especially in the legume strips of the intercropping system, through interspecific maize-legume interactions that determine changes in root traits. These results provide critical insights into the underlying ecological processes that promote the sustainability of species-rich agricultural systems on mollisols. • Soil aggregation in intercropped legume strips was higher than in legume monocultures. • Intercropped legume strip soil aggregation increased due to previous and current maize root growth effects. • Intercropping increased soil aggregation in soybean by in-season maize root but in peanut by pre-maize roots.