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Corn planting: How early can one go?

Calendar date is only one of many considerations in deciding when to plant


February 20, 2009  By Heather Hager

Researchers from various regions of the Corn Belt have estimated optimum planting dates for corn by examining how yield changes with planting date. Data from the northern US indicate that the corn yield in this region is greatest for planting dates in mid-April to early or mid-May and then decreases with later planting dates. The Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA), in its Agronomy Guide for Field Crops, gives optimal dates of “on or before May 7 in southwestern Ontario and May 10 in central and eastern Ontario.”  However, there is a fair amount of year-to-year variability in the relationship between yield and planting date. Indeed, knowing the optimal planting date is important, but many other considerations come into play when growers are deciding how early they can begin to plant corn in the spring. “When I talk to growers, the first thing would be the window of time they have to get their corn acres in. If it’s a grower who has eight or 12 days of corn planting, he probably has to look at starting as early as it’s fit to start,” says Fred Sinclair, product development manager for Pride Seeds.


Seed treatments can provide some degree of protection to seeds that must sit in cold soil, improving their chances of emerging and progressing as expected.

Greg Stewart, corn specialist at OMAFRA, and Mervyn Erb, an independent crop consultant located in Brucefield, Ontario, have similar ideas about taking an early window of opportunity to plant at least some fields in April. “If you have a window of opportunity in April when the soil is in good physical shape from a moisture, friability, and soil–seed contact perspective, then you’re tempted to plant on those days, regardless of whether the soil is still cold. If it starts raining on April 30 and rains for 10 days, you will have missed your opportunity to plant early, and that is probably much more of a yield sting than what you might experience by planting in soils that are cold,” says Stewart.


Erb notes that historically, there are only about 100 hours of opportune planting time in early May, and that is if the weather co-operates. “We might get a nice week of weather in April, and then it might get nasty and stay wet for a week or 10 days. Then you wake up and it’s May 6 and you wonder where the days went.  So you want to take advantage of every good situation you can.” What determines this early window of opportunity is the soil condition, specifically moisture and temperature. If the soil is too wet, explains Dr. Steven King, corn breeder with Pioneer Hi-Bred, the sidewalls of the planting trench will smear, causing problems for root penetration later on. “If you do something like that,” says Sinclair, “It’s going to haunt you for the rest of the season because you’ve done something you can’t fix.”

Determining soil fitness is a somewhat qualitative process. “What we do when we’re deciding whether to plant is to take a ball of soil in our hand and see how easily it crumbles,” says King. “If it stays as a ball, it’s not good enough to plant.  If the soil crumbles easily, then it’s fit.” 

Corn requires a soil temperature of 10 degrees C (50 degrees F) for good, even germination and emergence. The Agronomy Guide for Field Crops states, “If average soil temperatures are at or beyond 10 degrees C (50 degrees F), the soil conditions are favourable, and the weather forecast is predicting average to above-average temperatures, then early planting (i.e., April 15 to 25) of at least a portion of the corn crop is recommended. After April 26 or May 1 in areas receiving less than 2700 CHUs (crop heat units), it is generally advisable to pay less attention to soil temperature and to plant as soil moisture conditions permit.”

How early is too early?
The timing of corn planting in the spring has become earlier by 10 to 14 days since the 1970s. The ability to plant earlier is mainly attributed to advances in plant breeding and seed treatments, and perhaps changes in climate. Over the years, plant breeders have selected for hybrids that will tolerate cold, wet soil. “For a farmer to plant early to achieve that higher yield potential, he needs to be careful with the hybrid selection,” says King. “If he’s going to grow three or four different hybrids, he should plant the one with the highest stress emergence score first, and wait until the soil warms up before planting one that has a lower score.” 

Seed treatments for diseases and insects have also improved, say King and Sinclair. So even if the seed is planted in fit conditions and then must sit in the soil for a couple of weeks for whatever reason, it is protected from diseases and from insects that might start to feed on it. “Those improved seed treatments definitely have allowed us to plant earlier,” says King.

In terms of nailing down a date before which it is too early to plant, suggestions vary from April 15 to 24, all with the stipulation that soil conditions are fit. It is all about bet hedging and avoiding undue risk. “You’re taking a pretty big risk by putting a lot of corn in the ground April 15,” says Erb. “I guess if I had a really nice stretch of weather April 14 to 17, I might plant a little bit of corn, but I wouldn’t get too carried away; it is pretty early.”
It is not as simple as a decision to plant on the optimum date, says Stewart. “It has to be factored in against things like the size of the planter, how many acres you can plant in a day, how many acres you have to plant, and whether you have other operations that interfere with your planting efficiency. Therefore, you keep moving the start date of your planting back to accommodate optimum planting.” 

Although breeding and seed treatments have allowed earlier planting, it is still a good idea to consider the weather forecast. “Even if the ground is fit and it’s April, if there’s going to be cold rain or snow three days after planting, then I would really hesitate to plant,” says King. “It seems to be that the most sensitive time for a kernel in the ground is three days after planting. That corresponds to when the radicle, the root, just breaks the seed coat, so the seed is more vulnerable at that time.”

Of course, the debate as to how early is too early would be incomplete without knowing whether crop insurance specifies a “do not plant before” date, suggests Stewart. This was a topic of discussion amongst the Ontario Corn Producers’ Association, OMAFRA, and Agricorp in the early 2000s. Lindsay Barfoot, Agricorp account lead for grain and oilseed crop insurance plans, says that these discussions have impressed upon him that because of year-to-year and site-to-site variability, “it’s difficult to just choose a date on the calendar and say you can’t plant before that or you’re not eligible for insurance. We do require that producers are required for crop insurance purposes to use sound farm management practices, and honestly, we’ve found that to be a workable policy for us.”

Barfoot states that Agricorp relies on OMAFRA’s recommendations for sound farm management practices. “If our customers are doing anything that is not recommended or is outside of accepted practices, their insurance coverage could be jeopardized.” When a claim is submitted, the adjustors take into consideration what practices were used in planting the crop, including soil fitness.

In the end, it comes down to a judgment call. “It’s too early to plant when the soil conditions are not right,” says Jean-Marc Beneteau, a grower located in Essex county, Ontario, and a director of the Ontario Corn Producers’ Association. He stresses that it is important for a grower to know his own fields. “Farming is not a science, it’s an art.  It’s not that you stick a thermometer in the ground or you take a shovel of soil and you see that it’s fit, some people would say it’s too dry; some people would say it’s too wet, and some people would say it’s just right. It’s an art.” He says that nasty weather can occur in any month, so if the ground conditions are right, you plant, and if not, you wait.

“It’s hard to figure out when to plant at times,” concedes Beneteau. “That’s just part of being a farmer. When you have to justify it to a third party like crop insurance, that can be tough too. But I think they have excellent adjustors out in the field who understand when the farmer has pushed the limits too far. I think those instances
are rare.”

Once the fall harvest has been gathered, it is not too early to start thinking about spring planting. “Maintenance of your planter is critical,” says Sinclair. The best genetics and seed treatments are not going to substitute for planting at appropriate spacing and depth. After all, notes Sinclair, some things can be controlled and some cannot. “Do what you can to prepare beforehand because Mother Nature is usually going to throw something at you that you can’t control.


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