EDAH spraying in alternating two-row strips improves grain yield and resource use efficiency of densely planted maize in arid Northwest China

Canopy crowding and water limitation constrain the yield benefits of high planting density in arid regions. A two-year field experiment (2024–2025) in Northwest China evaluated canopy structure, leaf physiology, grain yield and quality, and resource use efficiency under full and deficit irrigation, two planting densities (93,000 and 114,000 plants ha⁻¹), and three spraying treatments: water in all rows, a plant growth regulator formulation containing ethephon and diethyl aminoethyl hexanoate (EDAH) in all rows, and EDAH and water in alternating pairs of rows. Alternating two-row spraying improved canopy architecture and within-canopy light distribution and was associated with better maintenance of ear-leaf photosynthetic function and lower oxidative damage at the sampled stages. It increased yield per plant by 1.04–6.02% relative to water spraying and by 3.71–7.86% relative to uniform EDAH spraying. Full irrigation combined with the higher density and alternating spraying produced the highest grain yields, reaching 16.24 and 17.53 t ha⁻¹ in 2024 and 2025, respectively. At the higher density, alternating spraying increased crop water productivity by 3.80–24.02% relative to water spraying and by 7.15–24.93% relative to uniform EDAH spraying. Under deficit irrigation at the higher density, thermal and radiation use efficiencies increased by 1.02–7.69% and 11.75–32.50%, respectively, relative to the two all-row treatments. Grain soluble sugar content was numerically higher under alternating spraying, whereas other quality responses varied among treatment combinations. These findings support alternating two-row EDAH spraying as a potential strategy to improve maize yield and resource use efficiency under the tested arid conditions.