OSCIA: Weather key in N recommendations for high-yield corn

Weather can make a big difference in the amount of nitrogen recommended for growing high-yielding corn. This is part of preliminary findings from a project led by corn specialist Greg Stewart of the Ontario Ministry of Agriculture and Food in Guelph, which is evaluating Ontario’s corn nitrogen calculator to determine the accuracy of its recommendations in high yield corn environments.

“We’ve seen a really significant increase in corn yields since we originally developed the corn calculator, so we want to see how it works when we’re in that high-yield range,” explains Stewart. “Generally, it works well, but does it perform when you have yields of 200 bushels per acre and higher?”

Using the current tool, growers can calculate how much nitrogen to put on their corn to generate the highest yield. Stewart is also looking at how N recommendations can be fine-tuned using real-time data like weather and soil N levels.

How is the research being conducted?

Experiments were carried out on six sites in 2011 and 2012 using seven different treatment combinations at each site. These included no nitrogen except starter fertilizer, four different pre-plant-only application rates of 50, 100, 150 and 200 pounds of N per acre, one split application (100 lbs. N per acre pre-plant and 50 lbs. side-dress) and a side-dress only application of 150 lbs. per acre. Several nitrogen management tools were evaluated for their ability to predict optimum nitrogen rates.

What has the project found to date?

So far, says Stewart, the corn calculator’s static recommendations for nitrogen application are fairly accurate but the weather ended up being a big factor in project outcomes to date. The first two project years were both very extreme — 2011 was cool with a wet spring that delayed corn planting and 2012 was hot and dry with a very early spring.

“In 2011, using only our corn calculator, we would have underestimated the amount of nitrogen needed, whereas in 2012, we overestimated, so the weather really needs to be taken into account if you’re going to do better than just a sit-down estimate,” says Stewart, adding that a soil nitrate test is a more reliable indicator than just looking at the leaves themselves.

The majority of Ontario farmers put nitrogen down before planting corn, says Stewart, with only 20 to 25 per cent side dressing in the knee-high stage. In order to capture the influence of the spring weather, it’s important not to apply all the nitrogen before planting; instead, put down a more moderate amount and then evaluate the weather and the soil before making decisions on any further application.

Cash cropper Ken Nixon, who farms north of London near Ilderton, is hosting some plot trials on his farm for the project. His applied nitrogen rate for maximum economic returns in 2011 was higher than he expected based on a combination of the corn calculator and his own experience on those fields. By contrast, using the same approach in 2012, his most economic nitrogen rates were significantly less that he had estimated.

“In 2011, the highest nitrogen application rate on our plots was 150 pounds per acre and our maximum yield was somewhere north of that. We never did uncover what the correct rate of N was, except we knew 150 lbs. wasn’t enough,” he says.

“In 2012, we didn’t want to repeat the same mistake, so added a 200-lb. treatment and had yields almost as good as 2011, but our rate of maximum economic return of nitrogen was about 90 lbs. per acre. Weather swings like this may be more part of our future going ahead so we may have to account for this somehow in our estimates.”

More information on this project can be found in Crop Advances. This project was funded by Grain Farmers of Ontario, with additional project support from the University of Guelph, John Deere and Premier Equipment in Elmira. OSCIA assisted with communication of research results.

— Lilian Schaer is a freelance writer and communications project specialist at Guelph, writing on behalf of the Ontario Soil and Crop Improvement Association (OSCIA).

Nitrogen tips for high-yielding corn

  • Make an in-season adjustment to nitrogen application instead of putting it all down before planting.
  • Use a soil N-test to get a real-time reading of a field’s nitrogen levels.
  • Consider the influence of the weather on the corn’s nitrogen needs.

-Greg Stewart, Ontario Ministry of Agriculture and Food

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