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.
