Comparative short-term performance of soil water management options for increased productivity of maize-cowpea intercropping in semi-arid Zimbabwe

Rainfall variability poses a great challenge to rainfed cropping in sub-Saharan Africa. We evaluated, over three cropping seasons, conservation agriculture (reduced tillage and mulching) and farmer prioritized conventional tillage- and mulching-based options on seasonal soil water retention, and subsequent productivity of maize (Zea mays L.) and cowpea (Vigna unguiculata Walp L.) in mono- and inter-crops in Eastern Zimbabwe. The experiments were established on sand and clay soils. The first cropping season (2014/15) received evenly distributed rainfall (hereinafter referred to as ‘wetter’), while the two succeeding seasons (2015/16 and 2016/17) had high incidences of intra-seasonal dry spells (hereinafter referred to as ‘drier’). Overall, conventional tillage had 10–31% and 27–40% more moisture than conservation agriculture treatments on sand and clay soils, respectively. Soil moisture was most retained in intercrop under mulch-based conventional tillage. Maize grain yield during the ‘wetter’ season on sand soil was highest and least (P > 0.05) in intercrop under conservation agriculture (2.3 Mg ha⁻¹) and mulch-based conventional tillage (1 Mg ha⁻¹), respectively. On clay soil, intercrop under mulch-based conventional tillage (2.4 Mg ha⁻¹) yielded the best. During the ‘drier’ seasons, intercrop under mulch-based conventional tillage achieved the best maize grain yield on both sand (1.5 Mg ha⁻¹) and clay (1.4 Mg ha⁻¹) soils. Mulching increased maize grain yield by 55–90% during the ‘drier’ seasons, but reduced water use efficiency (WUE) by approximately 15% during the ‘wetter’ season. Over the three seasons, cowpea grain yield did not exceed 1 Mg ha⁻¹ in both mono- and inter-crops. The study revealed contrasting short-term effects of soil water management options on soil moisture retention and intercropping productivity as dictated by seasonal rainfall variability and soil type. These findings point to the need for tillage and mulching typologies across soil types to minimize negative effects of rainfall variability on crop productivity.