Maize yield, water-use efficiency, and economic return response under graded deficit irrigation in an arid Iraqi environment

Water scarcity represents a major constraint on sustainable agricultural production and irrigation management in arid and semi-arid environments. Optimizing DI management to balance crop yield and water-use efficiency (WUE) is therefore critical as water availability declines. This study aims to experimentally assess maize responses to graded levels of deficit irrigation and identify an optimal irrigation regime that maximizes water productivity while sustaining yield under arid Iraqi conditions. A field experiment was conducted using a randomized complete block design (RCBD) with six irrigation treatments: a reference treatment of full irrigation (FI) and five deficit irrigation (DI) levels (DI5–DI25) in 5% increments, with three replicates per treatment. Crop evapotranspiration and irrigation requirements were estimated using CROPWAT based on local climatic, soil, and crop parameters. Treatment effects on grain yield, WUE, economic return, and economic water-use efficiency (EWUE) were evaluated using analysis of variance (ANOVA), followed by the least significant difference (LSD) test. The results demonstrated that FI achieved the highest grain yield; however, DI5 maintained statistically comparable yield while significantly enhancing WUE. In contrast, higher deficit levels (DI20–DI25) resulted in substantial reductions in yield, WUE, and economic return. The findings further indicated that irrigation level was the dominant factor governing maize performance, with limited influence from growth stages. Moderate deficit irrigation effectively improved water productivity while causing only a limited yield penalty, with yield reductions of 11% and 26.9% under DI5 and DI10, respectively. In contrast, severe water stress markedly impaired crop performance, resulting in yield reductions of 35%, 53.5%, and 56.6% under DI15, DI20, and DI25, respectively. Seasonal irrigation water application decreased progressively with increasing deficit severity, from 5977.76 m 3 /hectare under full irrigation (FI) to 5380.00 m 3 /hectare under DI25. The reduction in irrigation water application varied among crop growth stages, with the greatest reductions occurring during the lifespan treatment, followed by the flowering, elongation, and grain-filling stages. In contrast, the smallest reduction occurred during the germination stage. Despite the water savings, economic return declined from 2811.2 $/hectare under FI to 2478.0 $/hectare under DI5 and 1224 $/hectare under DI25, while economic water-use efficiency (EWUE) decreased from 2.35 to 2.12 and 1.13 $/m 3 , respectively. Therefore, slight deficit irrigation (DI5–DI10), combined with growth-stage-specific irrigation scheduling, represents a promising strategy for reducing irrigation water use while maintaining relatively high yield, water productivity, and economic returns, thereby supporting sustainable maize production under water-scarce conditions.