Optimising Irrigation Scheduling for High-Value Vegetables Under Deficit Water Supply in the North West Arid Zone

This study develops optimised irrigation scheduling protocols for high-value vegetable production under deficit water supply conditions in the arid zone of North West Nigeria, covering sites in Sokoto, Kebbi, and Zamfara States. Water scarcity is the primary agricultural productivity constraint in Nigeria's arid zone, and vegetable production for urban markets represents the highest-value use of limited dry season water. Optimising irrigation scheduling to maximise economic return per unit of water applied is therefore a critical agronomic management challenge. This study uses the FAO AquaCrop model calibrated for onion, tomato, and pepper under arid zone conditions to generate yield-water production functions. Model calibration and validation use measured crop growth, soil water, and yield data from two-season field experiments at the Sokoto State University of Science and Technology research farm. Deficit irrigation scenarios at 50, 70, and 90 percent of full crop evapotranspiration are tested across critical growth stage combinations. Economic optimisation analysis identifies the scheduling strategy maximising net income per cubic metre of water applied for each crop. Findings reveal that 70 percent ET replacement during vegetative stages combined with full replacement during reproductive stages (regulated deficit irrigation) achieves the highest water productivity for all three crops. Under this strategy, water use is reduced by 22 percent compared to full irrigation while maintaining 95 percent of maximum yield. Income per cubic metre of water is 28 percent higher under RDI than under full irrigation. The study recommends AquaCrop-based scheduling guidelines for arid zone vegetable irrigation advisory services.

Keywords: deficit irrigation, irrigation scheduling, vegetables, AquaCrop model, North West Nigeria.