Legume-Based Crop Diversification Reinforces Soil Health and Carbon Storage: Aggregates Mechanisms and Quantitative Evaluation

Abstract

Diversified cropping is a crucial management practice for increasing carbon (C) and nitrogen (N) sequestration in agroecosystems. However, knowledge gaps remain regarding the mechanisms by which diversified cropping affects C sequestration and soil quality. Herein, a field experiment across six-year was performed to explore the effect of three contrasting cropping systems (i.e., winter wheat/summer maize, winter wheat/summer maize-early soybean, and nature fallow) on soil quality and C sequestration, as well as their main drivers for both 0-20 cm and 20-40 cm soil depths. Diversified cropping increased SOC stock by 9% and the majority of the soil biochemical metrics in the topsoil despite a 40% reduction in the fertilizer application relative to wheat/maize. This is attributed to increased soil organic C content in large macroaggregates and enhanced microbial turnover due to diverse fresh residue inputs under diversified cropping. Alternatively, the soil organic C, microbial biomass C, C-acquisition enzyme activity, and dissolved organic C in large macroaggregates (> 2 mm) were increased by16%, 16%, 19%, and 7% in the topsoil under diversified cropping versus wheat/maize, respectively. Partial least squares path model displayed that increased C sequestration was mainly driven by microbial biomass C irrespective of the bulk- and aggregate scale. Furthermore, diversified cropping increased soil quality index by 1- to 2-folds relative to maize/wheat since increased aggregate stability benefited soil nutrient cycling and soil structure regardless of soil depth. Overall, increased SOC stock is dominantly driven by microbial biomass C, and the improved soil quality is mainly impelled by soil organic C and aggregate stability in responding to diversified cropping were expected to create win-win scenarios for agroecosystems.

Keywords: Diversified cropping, Legumes, Aggregates, Microbial biomass, C sequestration, soil quality