Judging when to get wheat seed into the ground is just one of several important decisions producers make each year. But some may not be paying enough attention to the importance of planting as early as possible, according to Jochum Wiersma, extension agronomist for the University of Minnesota-Crookston.
Wiersma recommends early planting to allow the different yield components the advantages of cooler growing conditions.
"We would expect that, as planting is delayed, our yield potential goes down," he says. "It doesn't happen every single year. 2008 would have been one of the beautiful exceptions, but I don't think we're going to have another year like 2008."
According to studies performed by the University of Minnesota and North Dakota State University Extension Service offices, the three yield components of wheat production all are affected directly by the planting date and the attending daily temperatures.
Components and growth
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Wheat yield is calculated as the number of tillers per square foot of surface soil multiplied by the number of kernels per spike times the kernel weight.
"The reason we talk about yield components in wheat is that they develop at different times of the growing season," Wiersma says. "When the crop emerges, the first thing it does is establish the number of tillers" per square foot.
The university studies show that wheat planted in late April developed two more tillers, on average, per square foot than wheat just planted 10 days later and seven more than wheat planted a month later. Considering this factor alone, a one-month delay reduced yield by 10 percent.
But the other factors also are affected, compounding yield loss, he says.
"In that 4.5- to 5.5-leaf stage, the growing point actually changes from just making leaves to actually initializing what is ultimately going to be the number of spikelets," he says.
Temperatures during this time affect the number of spikelets started, according to the studies. Wheat that was in the 4- to 5.5-leaf stage while temperatures averaged between 65 degrees and 70 degrees produced 16 to 17 spikelets per spike, while those at 75 degrees to 80 degrees produced two less spikelets per spike. The better option is to allow the wheat at this stage to spend more time in the cooler spring climates.
"You give that crop more chance to grow under conditions that, temperaturewise, on average, are more favorable," Wiersma says. "If you plant late, the likelihood that you're going to have an extended period of 65 to 70 degrees is, historically, a lot lower than if you'd planted in mid-April."
Kernel weight, the third component of wheat yield, also suffers with later planting, though the drop, according to the studies, is less severe than with tiller and spikelet production.
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Though there are several factors to consider in deciding when to plant wheat, Wiersma and the extension studies add weight to the argument for getting it into the ground as soon as possible.
