Enhancing soil aggregate stability and productivity in mature cocoa ( Theobroma cacao L.) -plantain (Musa spp) agroforest using legume-grass cover crops on acid ferralsols in Cameroon

Acid ferralitic soils in Cameroon exhibit low fertility and advanced degradation, hindering productivity and sustainability in mature cocoa-banana agroforestry systems. A study conducted from 2023 to 2025 aimed at promoting resilient, sustainable farming practices. Experimental split-plot designs with three replicates compared six treatments (Brachiaria humidicola L.+ Pueraria phaseoloides L.(B+P), Brachiaria humidicola L.+ Mucuna pruriens L. (B+M), Pueraria phaseoloides L.+ Calopogonium mucunoides L. (P+C), Stylosanthes guianensis L. + Desmodium intortum L. (S+D), Mucuna pruriens L. + Stylosanthes guianensis L. (M+S), and Desmodium intortum L. + Calopogonium mucunoides L.(D+C)) in two agro-ecological zones (Zone 4: Bokito and Zone 5: Kumba). Cover establishment occurred in 2023, with monthly monitoring of aboveground and root biomass production, ¹⁵N isotopic quantification of biological nitrogen fixation, semi-annual soil sampling (0–20 cm) for physico-chemical properties, commercial yield assessments for cocoa and plantain, erosion loss estimates, root-knot nematode counts (Radopholus similis, Pratylenchus spp.), and precise glyphosate consumption tracking. Results showed marked improvements across all parameters with the B+P association, yielding 13.9-15.1 t dry matter (DM) ha⁻¹ yr⁻¹ aboveground biomass and 5.2-6.8 t DM ha⁻¹ yr⁻¹ root biomass, fixing an average of 251 kg N ha⁻¹ yr⁻¹, increasing organic matter by 23%, raising pH by 0.5 units, and enhancing cation exchange capacity (CEC) by 32% after 24 months. These pedological gains translated to 31% higher cocoa yields (2.51 t ha⁻¹ vs. 1.99 t ha⁻¹ in controls) and 27% higher plantain yields (29.3 t ha⁻¹ vs. 23.6 t ha⁻¹). Additional benefits included 87% reduced water erosion, 96% lower glyphosate use (near-elimination), and 61% fewer root-lesion nematodes. Economic viability analysis indicated investment recovery by the second year via yield premiums. The B+P association emerges as the most effective and rapidly profitable practice for ecologically intensifying cocoa-banana agroforests in Cameroon. Future steps include long-term durability assessments under extreme climate scenarios, carbon sequestration and biodiversity quantification, and scaled dissemination via demonstration platforms and farmer agroecology training.