Introduction
In light of global warming, declining precipitation, excessive exploitation of water resources, and the continuous depletion of groundwater reserves, water scarcity in the agricultural sector has resulted in substantial yield reductions for most field crops. Although maize (Zea mays L.) exhibits relatively good adaptability to suboptimal growing conditions, drought stress remains one of the primary constraints limiting its productivity. Effective irrigation management represents a key agronomic strategy for achieving sustainable maize production and mitigating the adverse effects of water deficit. Additionally, the planting arrangement and spatial configuration influence crop performance by either intensifying or reducing inter-plant competition. These factors play a critical role in optimizing resource use efficiency. One of the principal objectives of optimizing planting arrangements in the field is to enhance water use efficiency. An appropriate planting arrangement can improve water productivity while reducing unnecessary evapotranspiration losses.
Materials and Methods
This study was conducted during the 2022 growing season at the Research Farm of the Faculty of Agriculture, Ferdowsi University of Mashhad, Iran. The experiment was arranged as a split-plot design based on a randomized complete block design (RCBD) with three replications. Irrigation levels (100, 85, and 70% of crop water requirement) were assigned to main plots, and three planting arrangements (75×11, 55×15, and 18×45 cm) with a constant plant density of 11 plants m⁻² were allocated to subplots. Irrigation water volume was measured using a volumetric water meter with an accuracy of 0.1 L, and separate irrigation was applied to each plot by controlling inlet valves. Irrigation was performed at five-day intervals. Measured traits included crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR), leaf area index (LAI), plant height, ear weight, and 300-kernel weight. For biomass and grain yield determination, plants were harvested from a central area of 6 m² after eliminating border effects. Water use efficiency (WUE) was calculated based on the amount of water applied to each treatment.
Results and Discussion
The results indicated that full irrigation under the 75 × 11 and 55 × 15 cm planting arrangements produced the highest crop growth rate. From emergence until 60 days after sowing, the 85% irrigation treatment combined with the 75 × 11 and 55 × 15 cm arrangements resulted in a higher relative growth rate compared to other treatments; however, beyond this stage, full irrigation treatments exhibited superior performance. At the early growth stages, the highest net assimilation rate was observed under 85% irrigation with the 55 × 15 cm arrangement. During the mid-growth stages and until the end of the growing period, full irrigation treatments across all planting arrangements demonstrated greater net assimilation rates. Reducing irrigation from 100% to 85% and 70% of the crop water requirement decreased the leaf area index by 11% and 27%, respectively. The greatest plant height (203 cm) was recorded under full irrigation with the 55 × 15 cm arrangement, whereas the lowest height (11% reduction) occurred under 70% irrigation with the 45 × 18 cm arrangement. The highest total dry matter accumulation was obtained under full irrigation with the 75 × 11 cm arrangement, while the lowest (35% reduction) was observed under 70% irrigation with the 18 × 45 cm arrangement. The maximum ear weight (1100 g.m⁻²) was recorded under full irrigation with the 55 × 15 cm arrangement, whereas the minimum value (39% reduction) occurred under 70% irrigation with the same planting arrangement. The highest and lowest grain yields were associated with full irrigation under the 55 × 15 cm arrangement and 70% irrigation under the 45 × 18 cm arrangement, respectively, representing a 61% difference. The harvest index was highest under full irrigation with the 45 × 18 cm arrangement and lowest under full irrigation with the 75 × 11 cm arrangement, with a 29% difference between them. Irrigation water use efficiency was greatest under full irrigation with the 11 × 75 cm arrangement and lowest under 70% irrigation with the 45 × 18 cm arrangement, differing by 29%.
Conclusion
Overall, evaluation of growth and yield indices indicated that up to approximately 60 days after emergence, the 85% irrigation treatment showed a relative advantage over other irrigation levels. However, thereafter, the 100% irrigation treatment resulted in the highest biomass and grain production. These findings suggest that moderate early-season deficit irrigation may allow improved water management in maize cultivation without substantial yield penalties. Among the evaluated planting arrangements, the 55×15 cm configuration was superior for most traits associated with dry matter accumulation and grain yield.