Effects of integrating vermicompost in maize-soybean intercropping on grain yield, soil fertility and carbon stocks

Declining soil fertility remains a key limitation to sustainable crop production in smallholder systems. This study investigated the effects of integrating vermicompost (VC) into maize–soybean intercropping on crop yield and soil nutrient dynamics across two contrasting agroecological zones: Hebei Province, China, and Mzuzu, Malawi. A split-plot field experiment was conducted with cropping systems—sole maize (M), sole soybean (S), and maize–soybean intercropping (MS)—as main plots, and fertilizer treatments—no fertilizer (CK), sole VC, inorganic fertilizer (NPK), and a combination of NPK and VC (NPK/VC)—as subplots, replicated three times. Intercropping enhanced land-use efficiency, with land equivalent ratio (LER) values of 1.21 in China and 1.31 in Malawi, indicating greater productivity than sole cropping. The combined NPK/VC treatment achieved the highest yields, increasing grain production by 31% in China and 33% in Malawi, while sole VC improved yields by 30% and 33%, respectively. Vermicompost-amended soils exhibited higher soil organic matter (15.9% in China; 27.7% in Malawi), total nitrogen (18.2% and 28.6%), available phosphorus (11.9% and 12.9%), and available potassium (6.6% and 9.0%) compared with NPK-only soils. These results demonstrate that integrating vermicompost with maize–soybean intercropping enhances land productivity, soil fertility, and nutrient availability while reducing dependence on synthetic fertilizers. The approach provides a practical, climate-smart pathway for improving food production and soil health in smallholder farming systems across diverse agroecological environments.