Water-nitrogen Management under Supplementary Irrigation through Rainwater Harvesting Technique for Improving Soil Fertility, Tomato Yield and Water Productivity in the West African Sahel

Abstract

Supplementary irrigation using harvested water is widely promoted in Burkina Faso and is increasingly adopted nationally as a suitable practice for sustaining and/or improving rain-fed production. However, under current land degradation conditions, this approach should be sustainable, with optimal water amounts matched to N fertiliser to optimise productivity while improving soil fertility. A two-year (2023 and 2024) split-plot field experiment was conducted at Gomtoaga village (12.24° N and 1.24° W), Koubri District, Burkina Faso, to identify an optimal water-nitrogen combination for improving soil fertility, yield, and water-use efficiency. Two forms of urea, pearled urea (PU) and deep placement of super granule urea (DPU), were combined with three water amounts (D100, D75, and D50), representing 100%, 75%, and 50% of tomato net irrigation, respectively. The results indicated that the PU + D75 combination increased soil microbial CO2 release (152%), microbial biomass (145%), OM (210%), C (215%), N (44%), and yield (34%), whereas DPU + D75 increased soil P (121%) and K (324%). The highest water productivity (43.34 kg/m3) and the lowest water cost (55.52 F CFA) for producing 1 kg of tomato were obtained under DPU + D50. Therefore, DPU + D50 and PU + D75 may be considered adapted practices for coping with water scarcity and improving land productivity, respectively. A cost-benefit analysis is required to identify the most beneficial combination by balancing farm returns and sustainable production.