Soil fertility matters most: Rainfed maize productivity under integrated water and nutrient management on granitic sands in sub-humid Zimbabwe

Agriculture in sub-Saharan Africa (SSA) faces the dual challenge of increasing food production while minimizing environmental degradation. Declining rainfed cereal yields are largely attributed to soil degradation, poor fertility management, and drought-related water deficits. While soil fertility and water conservation have traditionally been studied separately, integrated approaches may offer more sustainable solutions. This study evaluated the effects of water and fertility management practices on maize grain yield, Normalized Difference Vegetation Index (NDVI), and volumetric soil moisture content at Domboshawa Training Centre, Zimbabwe, across multiple seasons. A split-plot design tested four tillage systems and four fertility regimes, replicated four times. Seasonal water availability was assessed using the Water Requirement Satisfaction Index (WRSI), where values above 50 % indicate sufficient moisture for maize growth. WRSI values ranged from 38 % to 69 %, with the highest rainfall and crop performance in the 2011/12 season. NDVI values peaked at 0.6 in the 2015/16 season, also higher under treatments combining water management with manure + basal fertiliser, compared to other fertility options. Tied ridging significantly increased topsoil moisture by 36.5 % in 2013/14 season, though these moisture gains did not translate into higher yields. Grain yield was significantly influenced by fertility regime and seasonal rainfall, but not by water conservation practices. Peak yields reached 4.6 t ha−1 in 2013/14, with manure + basal fertiliser averaging 4.3 t ha−1. Findings suggest that in sub-humid environments with 600–800 mm annual rainfall, integrating organic and inorganic fertility inputs, should be prioritized over water management interventions to sustainably improve maize productivity.