Tied ridging and intercropping enhance soil fertility and Maize–Cowpea productivity across agroecological zones in Ghana

Declining soil fertility and erratic rainfall constrain rainfed smallholder crop production across sub-Saharan Africa. While practices such as maize–cowpea intercropping and tied ridging have the potential to enhance productivity and resilience, their combined efficacy across different agroecological zones remains insufficiently understood. This study assessed the impact of cropping systems (maize and cowpea monocrops and maize/cowpea intercrops) and landform management (tied ridging, ridging, and flat planting) on soil fertility and crop productivity across three agroecological zones in Ghana: Sudan Savannah (SS), Guinea Savannah (GS), and Forest–Savannah transition (FST). Field trials were conducted on smallholder farms over two cropping seasons (2023 and 2024) using a factorial experiment with treatments maintained on the same plots in both years. Result from the study revealed that, soil fertility indicators were generally higher in the FST zone than in the savannah zones, with greater soil organic carbon (21–28 %), microbial biomass carbon (28–48 %), ammonium (14–55 %), and nitrate (5–24 %) content. These conditions were associated with approximately 18% higher grain yields in the FST than in the SS. Grain yield was positively correlated with soil organic carbon and microbial biomass carbon, highlighting the importance of soil fertility for crop productivity. Across treatments, tied ridging increased grain yield by 30.9% and 35.7% compared with flat planting in years one and two, respectively. Intercropping improved land-use efficiency, with land equivalent ratios averaging 1.4 across years, indicating a clear productivity advantage over monocropping. Overall, tied ridging combined with maize–cowpea intercropping is a promising strategy for improving productivity in smallholder farming systems across variable agroecological environments.