Effects of tied ridging and mulching on soil moisture, crop yields and water productivity in rainfed sub-Saharan Africa: a meta-analysis for agricultural water management

Rainfall variability, recurrent dry spells, and limited soil-water storage constrain rainfed maize and sorghum production in sub-Saharan Africa. Tied ridging and mulching are widely promoted as low-cost soil and water conservation practices. However, their effects on soil moisture, grain yield and water productivity (WP) vary across crops and environments. This meta-analysis synthesized evidence from 101 peer-reviewed studies on tied ridging and mulching in rainfed maize and sorghum systems across sub-Saharan Africa. Treatment-control comparisons were analysed using bias-corrected standardized mean differences (Hedges' g) under random-effects models, with subgroup analyses by rainfall class, soil type, and region. Tied ridging significantly increased soil moisture in maize (g = 2.115; 95% CI: 1.508–2.722) and sorghum (g = 1.965; 95% CI: 1.379–2.551), with negligible heterogeneity. It also increased grain yield in maize (g = 1.159; 95% CI: 0.556–1.762) and sorghum (g = 1.193; 95% CI: 0.716–1.670), although maize yield responses were heterogeneous. Mulching significantly improved soil moisture in maize (g = 1.441; 95% CI: 1.139–1.744) and sorghum (g = 2.209; 95% CI: 1.282–3.136), and increased grain yield in maize (g = 1.809; 95% CI: 1.399–2.220) and sorghum (g = 1.850; 95% CI: 0.819–2.880). Water productivity evidence was limited, but mulching significantly improved maize WP (g = 1.977; 95% CI: 1.278–2.676), whereas tied ridging had no effect. Both practices enhance soil-water retention and productivity, but recommendations should be targeted by rainfall regime, soil type, crop, and local management constraints.