IRRIGATION DEPTH EFFECT ON MAIZE YIELD, NUTRIENT UPTAKE AND IRRIGATION USE EFFICIENCY IN BIRFARM, UPPER BLUE NILE, ETHIOPIA

Abstract

Water scarcity is a critical constraint to agricultural productivity in semi-arid regions like the Upper Blue Nile Basin, Ethiopia, where maize (Zea mays L.) is a key staple crop. This study was conducted to evaluate the effects of variable irrigation depths on maize yield, nutrient uptake, nitrate leaching, and irrigation water use efficiency. The research also assessed the performance of the AquaCrop model in simulating crop response to different irrigation regimes. A field experiment was carried out at Birr Farm over two consecutive irrigation seasons (2022/23 and 2023/24), using a randomized complete block design (RCBD) with five irrigation treatments: 50%, 75%, 100%, 125%, and 150% of crop evapotranspiration (ETc), each replicated three times. Data on irrigation performance, crop growth, yield parameters, nutrient dynamics, and water productivity were collected and analyzed using appropriate statistical methods. In addition, the AquaCrop model was calibrated and validated using field data to simulate maize growth and yield under varying water application levels. The results showed that irrigation depth significantly influenced irrigation efficiency, maize yield, and nutrient dynamics. The highest grain yield (6.08 t/ha) and biomass (14.94 t/ha) were achieved at 100% ETc, demonstrating the optimal balance between water use and crop response. Lower depths (50% ETc) conserved water but reduced yields, while excessive irrigation (150% ETc) increased nutrient uptake but led to substantial nitrate leaching and deep percolation losses. Application efficiency was highest at 50% ETc (67.5%) and lowest at 150% ETc (55%). AquaCrop showed strong agreement with observed data (R² = 0.99, NSE = 0.98), though it slightly underestimated evapotranspiration under severe water stress. The study concludes that full irrigation at 100% ETc optimizes maize yield and nutrient use efficiency while minimizing environmental impacts. The findings provide practical guidance for sustainable irrigation scheduling in water-limited environments. Adoption of the 100% ETc strategy, alongside model-based decision support tools like AquaCrop, can enhance water productivity and support resilient maize production in Ethiopia and similar agro-ecological zones.