Deep bed farming with maize–soybean intercropping improves maize yield and soil fertility in northern Malawi

In sub-Saharan Africa smallholder farmers face challenges of declining soil fertility, erratic rainfall, low crop yields, and food insecurity. Deep bed farming (DBF), a conservation agriculture-based approach promoted by Tiyeni in Malawi, shows potential to address these issues. This study evaluated the effects of integrating maize (Zea mays)–soybean (Glycine max) intercropping with DBF on maize grain yield and soil fertility. A split-plot design was used, with cropping systems (CSs) as main plots and tillage systems (TSs) as subplots, replicated three times across three cropping seasons. CS included mono-maize without fertilizer (M), mono-maize with 92 kg N ha−1 (M + 92 N), mono-soybean (S), and maize–soybean (MS) intercropping; TS comprised DBF and conventional tillage (CT). In season two, mono-maize without fertilizer was planted across all plots; in season three, maize was planted with 50 kg N ha−1. Results showed that MS intercropping under DBF significantly enhanced early maize growth—taller plants, more leaves, and greater leaf area compared to both mono-cropped maize under DBF and all CSs under CT. While M + 92 N yielded the most grain, intercropping showed favorable land productivity (land equivalent ratio > 1.16). Soybean yields were lower in intercrops but improved under DBF. Residual benefits from combined legume-based systems and DBF led to significantly higher maize yields and improved total N, available P, and soil organic carbon in subsequent seasons. Integrating MS intercropping with DBF enhances land-use efficiency and soil fertility, offering a climate-smart, conservation-aligned strategy for sustainable smallholder farming in Malawi and similar agroecological zones.