Corn Yield Response to Planting Date and Relative Maturity Hybrids

• Corn yields declined rapidly when planting after the last week of May.
• Full-season corn hybrids maximized yield at all planting dates except the first week of June.
• Later planted corn required fewer growing degree days to reach maturity making it possible to maintain similar relative maturity hybrids as with earlier planting dates.

Corn Planting Date Effects

The greatest opportunity for high yield potential in corn comes from planting a full-season relative maturity (RM) hybrid early.¹ Later planting dates generally decrease yield potential, increase kernel moisture and speed up corn plants’ vegetative development. Increased grain moisture from delayed planting also often results in reduced test weight. Test weight is a volumetric measurement that can be influenced by the size, shape and density of kernels. Stress from disease and insect damage, in addition to an early frost, can lower test weights by prematurely ending the grain fill period.²

Agronomy in Action Trials

Golden Harvest^® Agronomy in Action research trials studying corn planting date were established at 3 separate locations in IL, IA and NE in 2021 (Figure 1). 2 hybrids were selected within early (100-103 RM), mid (108 RM), and late (115-116 RM) groups to better understand hybrid response to planting dates. The first group of hybrids were planted in the last half of April as soil conditions allowed, and the subsequent 3 planting dates were performed at 2-week intervals thereafter. Each of the 4 planting dates were replicated 4 times in a split-plot design, where hybrids were grouped by maturity at each site. Flowering and black layer dates were recorded for each plot and trials were harvested with a research combine to assess yield, moisture and test weight. Plots from all planting dates were harvested when the earliest maturing hybrid in the first planting date reached 15.5% moisture.

Ways Corn Hybrids Adjust to Planting Date

June planting dates were seeded roughly 51 days after April planting dates, yet these hybrids reached maturity within 26 days of the April planting dates, indicating fewer growing degree units (GDUs) were needed to reach black layer with late-planted corn. The ability of corn plants to reduce the total number of days needed to reach maturity was achieved by shortening the total amount of time normally spent growing vegetatively by 20-25 days as compared to April planting dates (Graph 3). However, reproductive growth stages increased slightly in days with each delay in planting date, although fuller season hybrids always maintained a longer reproductive period than shorter hybrids at all planting dates. Full-season hybrids utilize the extended grain fill time to translocate sugars, which are converted into starch in developing kernels, typically resulting in additional yield potential. Planting full-season hybrids early also usually allows plants to flower in advance of heat or drought stress and reach physiological maturity earlier in the fall. Reaching physiological maturity earlier in the fall creates more opportunity to utilize warmer August temperatures to reduce grain drying costs and increase overall profitability. Uncertainty of harvest weather conditions and overall grain handling capacity can be reasons to select hybrids with a variety of RMs to spread out workload and ease drying costs in later planted corn.

In general, as planting date was delayed, harvest grain moisture increased across all hybrids. Grain test weight declined steadily as planting date was delayed. Earlier planted corn had more time for starch development in the kernel, leading to an overall increase in test weight.

Summary
Regardless of planting date, choosing a high yielding hybrid that is adapted to a given environment is the first step in maximizing yield potential. Fuller season hybrids should be utilized as much as possible prior to the last week of May to help extend the grain fill period and maximize yield potential. Relative maturity selection strategies should attempt to plant the fullest season hybrids for the area while also considering factors such as harvest and grain drying capacity. Areas with higher fall frost risk may need to transition quicker to earlier RM hybrids, although reducing 5-6 RM earlier than a normal full-season hybrid is usually sufficient.