University of Illinois Analysis: Determining How Late Is Too Late to Plant Corn and Soybeans
Date Posted: June 13, 2013
Urbana—With some of the Illinois corn crop still unplanted and other fields struggling due to heavy rainfall, growers must decide whether or not it makes sense to plant this late in the season, said University of Illinois crop sciences professor Emerson Nafziger.
“It’s very late to plant corn, so we need to decide first whether it makes sense to plant corn this late, and if not, whether the best option is prevented-planting insurance or replacement with soybeans, as crop insurance provisions allow,” Nafziger said.
Most corn-planting date studies include planting only through the end of May.
“Going beyond that is a little shaky,” he said.
“However, we have projected that corn reaches the point where we can expect 50 percent of maximum yield if it is planted sometime between June 15 and June 20.”
Based on this, June 15 to 20 might be considered the last practical dates to plant corn in order to produce grain, Nafziger added.
“We know that corn planted during or after the middle of June will produce fair to good yields in some years and very little yield in other years, depending on unpredictable weather that follows,” he said.
If corn is planted in mid to late June, planting a very early hybrid, having the option of harvesting the crop as silage if grain production looks unlikely, and getting good rainfall throughout the rest of the season will all improve the probability of a profitable crop, Nafziger said.
“The chances of having enough frost-free days to grow a crop are higher in central and southern Illinois than farther north, but higher water-loss rates and lower water-holding capacity of soils in the southern half of the state can cancel this advantage,” he said.
“It may also be difficult to get seed of very early hybrids, and because early hybrids are not developed for the central and southern Corn Belt, there is no guarantee that they will do well under late planting.”
If it’s too late to plant corn for enough yield to make a profit, or to at least make more than crop insurance would pay if nothing was planted, does it make sense to plant soybeans instead?
“We have run our soybean planting-date studies into the first or second week of June, but we still have to project expected yields past the last date we actually planted,” Nafziger said.
“As with corn, we would expect soybeans planted at the end of June or early in July to yield half what they would if planted early.
This is about two weeks later than the normal doublecrop planting date in southern Illinois, he said.
Doublecrop soybeans have averaged 72 percent of full-season soybean yields over the past 10 years at U of I’s Brownstown Agronomy Research Center, so using early July as the 50-percent-of-maximum-yield planting date seems reasonable, he added.
“We know that doublecrop (or very late-planted) soybean yields can range from zero to good, and there’s no way to predict, at planting, which end of this range they’ll be on,” Nafziger explained.
“As many found out in 2012, planting into bone-dry soils is not usually conducive to high doublecrop soybean yields.
"And in northern and central Illinois, doublecrop soybeans or soybeans planted (or replanted) in late June or early July have had a considerably lower rate of success than that of doublecrop soybeans in southern Illinois.”
One important difference between doublecrop soybeans and soybeans that are planted late but don’t follow wheat harvest is the available water left in the soil.
“Wheat removes a substantial amount of water from the soil as it matures, and in years with average June rainfall, the soybean crop that follows wheat has much less soil water available than does the crop that follows only the crop from the previous year,” Nafziger said.
“As is always the case, good rainfall through the rest of the season can cancel out this advantage, but it won’t eliminate it averaged over years.”
A soybean crop planted in mid to late June does not need to be managed differently than early-planted soybeans.
“Our recent research indicates that narrow rows tend to yield more regardless of planting date, and raising seeding rates seldom produces much advantage when planting late,” Nafziger explained.
“Unless a late-maturing variety was the first choice for earlier planting, there is no advantage to changing to an earlier variety for late planting.”
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