Corn Hybrid Response to Planting Date in the Northern Corn Belt

Growers frequently are concerned about the response of corn (Zea mays L.) to planting date. Early planting of corn is recommended because full‐season hybrids utilize the entire growing season, achieve physiological maturity before a killing frost, and start to dry, thereby increasing profit through reduced drying costs. The objective was to evaluate the influence of planting date and hybrid maturity on corn grain yield and harvest moisture in Wisconsin. Two or three corn hybrids ranging in relative maturity from 80 to 115 d were planted between 19 April and 22 June at six locations in Wisconsin from 1991 to 1994. In southern Wisconsin locations, the optimum planting date for grain yield of full‐ and shorter‐season hybrids ranged between 1 and 7 May, and was still at 95% of optimum between 9 and 18 May. In northern Wisconsin, the optimum planting date for grain yield of hybrids ranged between 8 and 14 May, and was still at 95% of optimum between 15 and 23 May. Grain yield did not change much when corn was planted between 24 April and 8 May. Grain yield of corn planted after 8 May in southern Wisconsin declined at the rate of 0.5 to 1.1% d−1 over the next 2 wk, accelerating to 1.3 to 1.9% d−1 and 2.0 to 2.8% d−1 over the next two 2‐wk periods. Grain yield of corn planted after 8 May in northern Wisconsin declined at the rate of 0.2 to 1.7% d−1 over the next 2 wk, accelerating to 1.7 to 2.2% d−1 and 3.2 to 3.8% d−1 over the next two 2‐wk periods. The decision to begin planting corn early should be based on soil temperature and field conditions. After 20 April, planting of full‐season hybrids should proceed as rapidly as field conditions allow. The date to switch from full‐season to shorter‐season hybrids depends on numerous factors, including corn price and drying costs, but generally occurs by mid‐May in southern and by late May in northern Wisconsin.