Optimizing planting density and post-silking growth degree days effectively accelerates summer maize grain dehydration

The efficacy of mechanical maize grain harvesting is significantly enhanced by reducing the grain moisture content at the stage of physiological maturity. Nonetheless, the determinants affecting grain moisture content during this phase remain inadequately explained. Field experiments were conducted from 2021 to 2023, including planting density experiment and sowing date experiment. The preeminent contribution to the grain dehydration rate was identified as the husk's transpiration rate, succeeded by the leaf transpiration rate, culminating in a synergistic contribution ratio of 53.1 %. Excess water in the ear was capable of being redirected back into the ear-pedicel, with the majority of it being lost to the air through the husk, and only a small portion being returned to the plant stem. The grain moisture content was significantly affected by growing degree days (GDDs) at the grain filling stage. An escalation in planting density precipitated variegated performances among the two hybrids: for each increment of 100 degrees C d in GDDs, the moisture content variation for DH187 across densities ranged from between 6.3 % and 6.9 %, contrasting with a narrower range of 6.0-6.2 % for DH605. Grain moisture content was jointly regulated by the moisture content of both the husk and leaves, as well as the rate of water loss from the grain surface. Higher GDDs from silking to the physiological maturity stage, a larger ear angle, and increased looseness of grain arrangement likely accelerated the rate of water loss from the grain surface, thereby reducing the grain moisture content at physiological maturity.