With corn planting off to a very slow start this year, it’s not surprising that very few people have been worrying about getting soybeans planted. Although in recent years, early planting of soybean helps increase yield potential, corn typically loses yield faster than soybean as planting is delayed. Consequently, it is appropriate to plant corn first, before soybean, according to University of Illinois crop sciences professor Emerson Nafziger.
How early is too early when it comes to soybean planting?
“Based on planting date responses we have seen in recent years, we consider the period from mid-April through the first week of May as providing the best chance at high yields,” Nafziger said. “In general, the planting date response of soybean parallels that of corn on a percentage (not bushel) basis, but lags the response in corn by a week to 10 days,” he said.
According to trials run under relatively good conditions over the past three years, daily yield losses for soybean are about 0.3, 0.4, and 0.5% per day of planting delay for the first, second, and third 10-day period in May. Total loss in potential is about 15% by the end of May, compared to about 25% loss, on average, for corn planted that late.
“It is clear that early planting only increases the yield potential in soybean,” Nafziger said. “It will do little to prevent yield loss if weather conditions, especially in August, result in crop stress. And, in a season like 2012, with very dry conditions through July and then adequate rain in August and September, planting early can actually decrease yield in some cases. This happens because extended stress through flowering can cause the soybean plant to lose its ability to respond favorably to improved conditions by setting and filling more pods. Conversely, a wet start to the season followed by dry weather will often mean more benefit from early planting, if that means producing and starting to fill more pods before stress begins,” he said.
Soybean’s sensitivity to day length means that later-planted soybeans flower in fewer days than earlier-planted ones, so planting delays only modestly delay maturity, Nafziger said.
“We can expect maturity to be a day later for every five days or so later we plant, but this varies widely from year to year,” Nafziger said. “The response to day length also means that there’s no reason to switch to earlier varieties with late planting; in fact, earlier-maturing varieties tend to have less ability to come back from periods of mid-season stress than do later-maturing ones. This is why we saw later varieties yield more than early ones in some of our trials in 2012.