Soil Water Balance Modelling for Optimising Deficit Irrigation in Dry Season Vegetable Production in Northern Nigeria

This study develops and applies a soil water balance model for optimising deficit irrigation scheduling in dry season vegetable production across the semi-arid zone of northern Nigeria, contributing to improved water productivity in water-scarce farming systems. Water scarcity is a fundamental constraint on dry season agricultural production in northern Nigeria, making deficit irrigation, in which crops are intentionally subjected to mild water stress at less sensitive growth stages, an attractive strategy for maximising output per unit of water applied. However, the optimal deficit irrigation strategy varies with crop type, soil texture, evaporative demand, and available water storage capacity. This study calibrates the AquaCrop crop model for three vegetable crops, namely tomato, onion, and pepper, using field data from experiments conducted at three sites in Kano, Sokoto, and Gombe States over two dry seasons. Calibrated model simulations generate yield-water production functions that quantify the trade-off between water application reduction and yield loss at each irrigation strategy. Economic optimisation identifies deficit irrigation strategies that maximise net return per cubic metre of water applied. Findings reveal that tomato and pepper can tolerate up to 30 percent deficit irrigation during vegetative stages with less than 8 percent yield reduction, while onion is more sensitive to deficit at all growth stages. Optimal water productivity strategies improve net revenue per cubic metre by 22 to 35 percent compared to full irrigation. The study recommends AquaCrop-based irrigation advisory services for extension delivery.

Keywords: deficit irrigation, soil water balance, AquaCrop model, vegetable production, northern Nigeria.