Cover crops as drivers of the rhizosphere microbiome: Impacts on a subsequent common bean crop in degraded soils

Abstract

Soil degradation is a significant challenge in modern agriculture, often leading to reduced soil fertility and productivity, threatening ecosystem functionality. Cover crops (CC) are promising tools to modulate the rhizosphere microbiome and restore soil functionality. A two-year field experiment was conducted on soils with approximately 50 years of continuous monoculture to assess the short-term effects of gramineous (brachiaria, triticale, and oat) and legume (vetch and melilotus) CC species on rhizosphere bacterial community composition and structure, key physicochemical and microbiological properties of the rhizosphere soil, soil-borne fungal disease incidence, and common bean yield. The introduction of CC primarily induced species-specific shifts in microbial composition and relative abundance in the rhizosphere. Vetch and melilotus enriched bacterial communities associated with nitrogen cycling, whereas brachiaria, oat, and triticale promoted favoured bacteria associated with carbon and sulphur cycling. These microbial changes were accompanied by improvements in rhizosphere soil properties: vetch and melilotus increased nitrogen content, microbial biomass, enzymatic activity, and water-holding capacity, while gramineous CC species (particularly brachiaria and oat) enhanced aggregate stability. All CC reduced soil-borne fungal disease incidence, with vetch and melilotus showing the strongest suppression, and increased common bean yield compared to common bean monoculture without CC. These findings underscore the potential of strategically selected CC, particularly legumes, to promote the ecological recovery of soils degraded by long-term intensive use, and enhance common bean productivity, with direct implications for the sustainability of cropping systems.