We started planting corn on April 14. Recent planting progress statistics from USDA-NASS indicate that corn planting is progressing slowly in the northern Corn Belt. Only 1% of corn acres had been planted in Wisconsin as of April 17.
The date that produces maximum corn grain yield varies by field, tillage practice, hybrid and latitude. Every year since 1991 we have established a planting date experiment at Arlington, WI. On this farm, if you could plant all of your corn on one date and wanted to maximize yield, then the best date would be May 1 (Figure 1). As expected, we have observed a step increase for yield every decade. However, the maximum yield planting date has not shifted much (April 28 to May 4). The economic optimum is going to be earlier than these dates, because typically earlier planted corn is drier at harvest. The planting date “window” when we can be within 95% of the maximum yield is between April 18 and May 16. Grain yield decreases 0.5 bu/A per day on May 15 and accelerates to 2.5 bu/A per day on June 1.
For southern Wisconsin we typically recommend to begin planting anytime after April 20 as long as field conditions are fit. For northern Wisconsin anytime after April 30 is appropriate. Soil temperature is not a consideration after these dates. However, we do pay attention to the short-term weather forecast. If cold, wet conditions within 48 to 72 hours of planting are predicted, it is prudent to wait until weather is more favorable. We lost trials at Seymour and Fond du Lac in 2006 when we planted ahead of a snow storm; the only corn that survived was over the drain field. This phenomenon is called imbibitional chilling. There is not a lot of field data to support this practice and it has only happened to us twice over the last 20 years. The challenge as to when to begin planting, is what to do between April 10 when insurance coverage starts and the typical April 20 (southern) and April 30 (northern) start dates. Soil temperature is a good guide during this period. Corn doesn’t grow much when temperatures fall below 50 degrees F.
Figure 1. Corn grain yield response to planting date by decade at Arlington, WI. The 1970s included data from experiments conducted during 1974, 1976, 1977, and 1978; 1980s included 1980 and 1981; 1990s included 1991 to 1999; 2000s included 2000 to 2009; 2010s included 2010 to 2015.