Optimum corn planting dates vary with latitude. The northern Corn Belt is limited by heat units during the growing season, especially during the spring when cool, wet soils delay planting and during the fall when early frosts kill plants prematurely. Within Wisconsin we often find that optimum corn planting dates are later 'up-north' than in southern Wisconsin and that yield loss accelerates more quickly resulting in a shorter planting window.

The general shape of the planting date response at a location has been described previously. The last time a statewide corn planting date experiment was conducted at numerous locations was during 1991-1994 (Lauer et al., 1999). Full- and shorter-season corn hybrids were planted on five to eight planting dates between April 19 to June 22.

For the northern sites of Ashland, Spooner and Marshfield, the date when maximum corn yield occurred averaged May 12, while the southern sites of Hancock, Arlington and Lancaster were one week earlier averaging May 5 (Table 1). Corn yields were still at 95% of the maximum yield on May 17 in the north and May 12 in the south. By June 1, corn yield was decreasing at an average rate of 2.3 bu/A per day in the north and at a slower rate moving south to Lancaster.

Table 1. Corn grain yield response to planting date of full-season hybrids at various locations in Wisconsin during 1991 to 1994 (derived from Lauer et al., 1999).

Location				Date of:		Rate of daily yield (bu/A) loss on:
(North to South)	Full-season Relative Maturity	R2	Maximum yield Bu/A	Maximum yield	95% of max yield	May 10	May 20	June 1
Ashland	85	0.43	131	May 11	May 17	0.9	1.4	2.0
Spooner	85-90	0.55	109	May 11	May 15	0.0	0.8	2.0
Marshfield	100	0.68	147	May 14	May 19	0.5	1.5	2.7
Hancock	110	0.40	175	May 5	May 9	0.9	1.7	2.7
Arlington	110-115	0.57	185	May 7	May 14	0.7	1.3	1.9
Lancaster	115	0.37	179	May 3	May 12	0.9	0.9	0.9

Optimum corn planting dates likely vary with farm, hybrid, field, tillage system and other management factors. In northern Wisconsin, these factors along with latitude result in lower yield potential and when combined with grain moisture and drying costs described previously often makes corn production marginal as we move north.

Optimum Corn Planting Dates Are Later 'Up North'

Further Reading