Work

Identifying contrasting drivers of maize and legume yield gaps in Zimbabwean smallholder farms using a locally parameterised crop model

Year: 2026

Type: article

Abstract: Problem In sub-Saharan Africa, cereal and legume yields on smallholder farms typically fall far below both potential and water-limited levels. Understanding the drivers of yield variability in these farms is critical to design relevant pathways for sustainable intensification. Objective Our objective was to assess the relative contribution of water, nitrogen (N) and reducing factors (weeds, pests and diseases) on the yield of maize ( Zea mays L.), and grain legumes (groundnut - Arachis hypogaea L., cowpea - Vigna unguiculata (L.) Walp. and pigeon pea - Cajanus cajan (L.) Huth) in smallholder cropping systems. Methods Crop growth variables and yields were monitored in 99 cropping situations in on-farm trials and farmers’ fields, during two growing seasons in Murehwa district, sub-humid Zimbabwe. We identified ‘best-managed situations’ where yield reducing factors were minimized, yet with still pest and disease issues for legumes. The STICS soil-crop model was parameterised and evaluated for its ability to reproduce the observed variability in crop growth in these best-managed cropping situations that were assumed to be closest to model assumptions. The model was then used to compute the share of the yield gap caused by stress from water, N and other reducing factors. Results The model reproduced the variations in observed grain yield and aboveground biomass in the best-managed cropping situations with R 2 of 0.86 and 0.74, respectively. The computed yield gap between observed and potential yield due to water stress was large for pigeon pea, small for maize, and negligible for groundnut and cowpea. For maize, observed yield was close to simulated water- and N-limited yield (Ywn) when 160 kg N ha −1 and best management were applied. For legumes this gap between actual yield and Ywn was large across all cropping situations, even with best management. Conclusion Under the sub-humid climate of this study, maize yield was much more limited by N than water stress. Our study suggests a larger impact of pests and diseases on legumes than on maize, in the smallholder context of the two-year on-farm monitoring. Our findings highlight that reducing pests and diseases is critical to close legumes yield gap.

Source: Field Crops Research

DOI: 10.1016/j.fcr.2026.110716