When to begin planting is an important decision in managing corn. During the month of May we typically see a grain yield decrease of 30%. Not only does yield decrease, but grain moisture increases adding drying costs and decreasing profitability. What is not well understood are other risks that can influence this decision. Risks that can change dramatically as planting date is delayed include increased pest pressure (especially insects such as corn rootworm), increased lodging potential, greater chance of poor kernel set which in turn lowers grain yield and reduces test weight.

Grain yield ultimately integrates many of these risks. Last week we described what happens to grain yield as planting date is delayed. This week I want to describe what happens to ethanol yield (Figure 1). At Arlington, ethanol yield is maximized by planting around May 1. The planting window when ethanol yield is still within 95% of the date when maximum ethanol yield occurs, is about 10 days before and after May 1. Like grain yield, ethanol yield decreases as planting is delayed. By June 1 one-third of the potential ethanol production is lost. The response is more dramatic for full-season hybrids than for shorter-season hybrids. Around May 25 shorter-season hybrids produce more ethanol yield than full-season hybrids. Maturity switch dates for corn ethanol yield are similar to the switch dates for corn grain yield.

The major driver for corn ethanol yield is grain yield. Planting date affects both grain yield and ethanol yield. From a processing perspective, it also affects recoverable ethanol per bushel of grain. Recoverable ethanol ranged from 2.8 to 2.9 gallons per bushel during May, but only 2.6 to 2.8 gallons per bushel in June. So June planted corn has both reduced ethanol yield and recoverable ethanol.

Figure 1. Corn ethanol yield response to planting date and relative maturity (RM) at Arlington, WI.