Regenerative nutrient cycling in maize–soybean intercropping: biological nitrogen fixation, integrated fertilization, and climate-smart performance in West Africa

Résumé

Smallholder maize-based systems in sub-Saharan Africa face persistent constraints from declining soil organic carbon (SOC), low nitrogen use efficiency (NUE), and increasing climate variability, all of which threaten productivity and long-term soil function. Regenerative nutrient management has therefore attracted growing attention as an approach for tightening nutrient cycles, reducing unnecessary dependence on synthetic nitrogen, and improving the ecological resilience of farming systems. This review evaluates maize–soybean intercropping as a regenerative nutrient-cycling strategy for West African smallholder systems, with particular emphasis on humid southeastern Nigeria. The review focuses on three linked components: biological nitrogen fixation (BNF) by soybean and its enhancement through rhizobial inoculation, integrated organic–inorganic fertilization, and climate-smart performance assessed through productivity, SOC, soil respiration or soil CO₂ dynamics, and nitrogen-use efficiency indicators. A structured literature review was conducted between January and March 2026 using Web of Science, Scopus, Google Scholar, and selected institutional repositories. Evidence was organized into five domains: BNF and inoculation performance, integrated fertilization, SOC and greenhouse-gas-related indicators, productivity and NUE, and adoption constraints. Across tropical cereal–legume systems, inoculated soybean frequently showed strong nodulation and yield responses, but response magnitude varied substantially with soil acidity, phosphorus availability, moisture regime, and inoculant quality. The available evidence supports maize–soybean intercropping with inoculation and integrated fertilization as a promising pathway to improve land-use efficiency, diversify nitrogen sources, and reduce mineral nitrogen dependence, although gains in SOC and greenhouse-gas mitigation remain more context-dependent in humid tropical environments with rapid decomposition dynamics. The novelty of this review lies in combining regenerative nutrient-cycling concepts with a multi-indicator climate-smart framework for maize–soybean intercropping in humid West Africa, while identifying critical evidence gaps for southeastern Nigeria.

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