Supplemental Irrigation Water Management Using Rainwater Harvesting Basin for Improving Soil Fertility, Maize Yield and Water Productivity in Semi-arid Climate of Burkina Faso

Last decades, rainwater harvesting basins are promoted in Burkina Faso for securing rain-fed agriculture. However, sustainable water management is highly desired and crucial for agriculture in erratic climatic conditions exacerbated by soil degradation. In order to pinpoint suitable water depth optimizing sustainably land and water productivity while improving and/or maintaining soil fertility, an experiment was implemented in Gomtoaga village at Koubri district during two consecutive rain-fed cropping seasons (2023 and 2024). The study tested three irrigation water depths (D50%, D75% and D100%), representing 50%, 75% and 100% of the maize crop evapotranspiration (ETc), against a control of D0% through a randomized complete block design in three replications. The compost was applied at a rate of 7.5 t/ha during tillage and fertilizer NPK (14:23:14) and urea (46%) were applied respectively 15<sup>th</sup> and 50<sup>th</sup> days after transplanting. Irrigation was applied at two days interval in case of no rain. When rain occurred, irrigation was postponed to the following interval. The results revealed that soil chemical properties were not significantly affected by water fluctuation. No change was observed in pH, organic matter (%), C (%), N (%), P (mg/kg), K (mg/kg) and the ratio C/N in water treatments when compared to D0%. While the application of 100% ETc improved microbial biomass from 50%, the water level of 75% Etc increased the release of CO<sub>2</sub> from almost 99%. The optimal water depth (D50%) exhibited the highest yield (≈ 5957 kg/ha) with an increase of 24% compared to other treatments resulting in the highest water productivity (17 kg/m<sup>3</sup>) and the lowest irrigation cost (111 f cfa/kg of maize). We advocate farmers could adopt the compromise supplemental water level of 50% of ETc in rain-fed maize system as a water-wise tactic to secure sustainably the production when collecting rainwater surmounting drought spells in dry prone area.