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Prairie corn: Agronomics and economics

A four-year project in Manitoba has some notable findings on tillage economics and the reliability of heat unit ratings

As Prairie farmers consider growing some of the shorter-season corn hybrids coming onto the market, they still have questions whether they should even risk trying them, and which hybrids have the best chance of success.

After completing three years of the four-year Corn Agronomy Project, researchers are beginning to provide a few answers — and more questions.

The Manitoba Corn Growers Associa­tion is co-funding the project along with the Western Grains Research Foundation and Growing Forward II. The project focuses on four key areas — crop rotation and phosphorus fertility strategies, residue management, row spacing and evaluating the corn heat unit (CHU) model for Western Canada.

“The project is meant to complement the work that’s being done in the private sector to breed and select for early maturity corn that’s adapted to Western Can­ada,” says principal researcher Yvonne Lawley of the University of Manitoba. “It recognizes that farmers need good information about how to incorporate corn into their production systems and crop rotations.”

Corn after canola

Researchers are giving special attention to how corn fits with canola, as there is little information about how they perform together. Most corn research has come out of Eastern Canada and the U.S., where corn, soybeans and wheat are the most common rotation.

Canola is non-mycorrhizal, meaning it doesn’t depend on soil fungi. But corn is highly dependent on mycorrhizae, especially for early-season phosphorus uptake.

“Studies elsewhere have shown a big challenge with early-season plant growth and uptake of P when corn was grown after canola,” says Don Flaten of the University of Manitoba, who leads the corn fertilization study. “We are looking at whether placing some P fertilizer and zinc fertilizer close to the seed row would help.”

In the trials, corn followed either canola or soybeans. The corn received five starter P treatments, side-banded at planting. Treatment 1 was the control, with no starter P. Other treatments were 27 lbs. P2O5/acre and 54 lbs. P2O5/acre and the same rates applied as MAP (monoammonium phosphate, 11-52-0) or with MicroEssentials SZ (12-40-0-10-1) zinc. (Some studies have shown that corn on canola stubble may be prone to zinc deficiency but these trials didn’t show any response to starter zinc, most likely because test sites were not deficient).

Corn on canola stubble. (Left: 27 lb. P2O5/ac. MAP spring sideband versus control (no P).
photo: Magda Rogalsky

“With the application of starter P, we saw substantial increases in early-season growth — in some cases twice as much — than the control that received no P, especially when corn followed canola,” says former master’s student Magda Rogalsky, who worked on the project.

“Once we got to silking and pollen shed, we saw further maturity differences. In some cases, the control was three to seven days behind the starter P treatment plots. So we had advanced maturity with the application of starter P, regardless of the preceding crop.”

Flaten says starter fertilizer may allow planting of a higher-yielding, longer-season corn hybrid. “Or if producers want to reduce their risk, they would be able to harvest a shorter-season hybrid three to seven days earlier.”

Corn grain moisture decreased by up to three per cent when starter P was applied on corn following canola. Rogal­sky says this reduces the need for drying capacity and allows an earlier harvest, potentially avoiding poor field conditions.

Corn grain yield increased by 11 bu./ac. with the highest rate of MAP compared to the control, regardless of the preceding crop.

Economics of corn in rotation

Manitoba crop insurance crop rotation data shows that corn yields well after soybeans, but the researchers are also using the data to see if the agronomics and economics match.

Corn/soybean/corn/soybean definitely comes out as the most profitable rotation so far, says University of Manitoba agricultural economics professor Derek Brewin, based on a model that compares average provincial crop yields with current crop prices.

But before farmers rush into a corn/soybean rotation, there are a few caveats. It’s still risky to grow corn and soybeans in certain areas of Western Canada given the short growing season and weather variability. Continuous soybean/corn rotations aren’t the best from the agronomic standpoint of disease, pest and fertility management. And Brewin has not yet factored long-term variations in yield and price averages into his economic model.

“We would like to assess if we put a normal range of production and price shocks into the system, which rotations would be the most profitable over the long run or face the least number of loss years,” says Brewin.

Managing all that residue

The residue management component of the Corn Agronomy Project compared four tillage treatments for soybeans following corn — conventional double-disc, high-disturbance vertical tillage, low-disturbance vertical tillage and strip tillage.

There was no significant difference among them in soybean emergence, final plant stand or yield. But an economic analysis showed significant cost and time savings with strip till. Conventional double-discing (requiring two passes) cost just over $32 per acre, whereas strip till cost around $19 an acre.

“For an average size farm in Manitoba (around 1,100 acres) strip till could save a farmer approximately $11,800 to $14,600 per year compared to other tillage systems,” says Patrick Walther, a graduate student who performed the economic analysis. “Furthermore, strip till, as a one-pass system, showed time savings on an average farm of 1.1 to 3.7 days compared to vertical till and double disc, respectively.”

Strip till could potentially be a better fit with western Canadian no-till practices.

“Strip tillage gives you the best of both worlds because you leave some residue, but you also do tillage where you plan to create a seedbed for your next crop,” says Lawley. “One of the reasons that strip till is of growing interest to farmers in West­ern Canada, is that they can do residue management and band fall or spring fertilizer at the same time.”

Fertility/tillage combinations

Flaten’s team did experiments in 2015 and 2016 to compare response to P fertilizer rates and methods of application in corn following wheat in both a strip till and tandem-disc tillage system. Rates were again a control (zero fertilizer), MAP at 27 lbs. P2O5/acre and 54 lbs. P2O5/acre fall deep-banded, plus the same rates spring side-banded at planting.

“The spring side-banded MAP treatment was better than fall deep-banding in terms of greater early-season biomass, advanced maturity, and a reduction in grain moisture,” says Rogalsky.

The fall MAP was banded at a depth of about five inches below the seed, which is quite a bit lower than most farmers would place it.

“It might have taken the corn seedling longer to reach the deep-banded P than it took to reach the side-band, which was only an inch below and two inches beside the seed so the P band was closer and more precise for the side-banded in the springtime,” says Flaten.

“The take-home message is that corn growers in Manitoba have a lot of options for managing corn residue,” says Lawley. “We did not find differences in soybean yields between any of our tillage treatments. That’s good news in that we can look at tools other than just the double disc. So moving towards vertical tillage where you’re able to travel faster and do more shallow incorporation of residue, there’s that option. As well, if you’re interested in protecting soil from erosion, strip till also yielded the same as the double-disc treatment.”

Heat Units versus actual season length

Further research is looking at how corn heat units (CHU) ratings compare with actual time to maturity for corn hybrids planted in West­ern Canada.

Paul Bullock’s team from the Univer­sity of Manitoba evaluated six test sites in Manitoba and two in Alberta over two years, keeping accurate measurements of how the corn developed in different weather conditions. They compared three longer-season hybrids rated at 2550, 2600 and 2700 CHU and two shorter-season ones rated at 2200 and 2300 CHU. All the hybrids needed more heat units than their CHU rating said they needed to reach maturity.

“The actual heat unit requirement for the longer-season hybrids was a little more, but the short-season varieties required a lot more,” says Bullock. “That basically confirmed producers’ concerns about just going with the CHU rating to select a suitable hybrid for their location.”

Bullock then began to look at alternatives that could better quantify the heat requirements.

“We looked at GTI (general thermal index),” says Bullock. “It’s hard to make a strong recommendation based on two years of the study, but GTI seemed to be more consistent in terms of how much heat was required from location to location. So, it’s hinting that it could be a better type of heat unit than the CHU.”

But switching to another heat unit is one thing — knowing how many you can expect on your farm is another.

“For that we use 30 years of data. We’ve done that for CHU but we haven’t done that for GTI,” says Bullock. “So if we say we need 1400 GTI, we don’t know how many of these heat units we get in a year because that data has not been analyzed. We need to collect more information and try to confirm what might be a better heat unit rating because it would be a significant shift if we said to the industry ‘Don’t use CHU but use GTI instead.’”

Relative maturity (RM) is another method that seed companies use to rate corn hybrids. It gives a range of the number of days required for a hybrid to reach maturity. Each RM rating is specific to the seed company developing the hybrid and is relative to its own check variety, which is different for each company. Bullock’s team analyzed data from corn trials over the last few years to see how reliable and consistent RM ratings are.

“Even between the companies, there is some kind of consistency,” says Bullock. “When we took the RM rating for all the different companies and compared it to the CHU rating, there was an even tighter relationship, and again consistency between companies is very high.

“That means producers probably don’t need to be too concerned about where they get their seed for their grain corn, because it should be reasonably consistent.”

That said, RM may not be any more useful as a guide to assess maturity than CHU. “If we say CHU is not working well, and now we’re saying that RM is actually quite correlated to CHU, we just don’t see RM as being any better,” says Bullock.

Cool nights affect CHUs

Bullock has also investigated whether the varia­tion in the number of CHUs required could be due to temperature shock caused by the colder summer nights that are more common on the Prairies.

After plotting data from the test plots and looking at the number of hours the corn spent below 4.4 C, researchers found, counterintuitively, that hybrids that experienced more cold nights actually required fewer CHUs from planting to maturity.

“I have no explanation for this,” says Bullock. “Is it a plant coping mechanism?

He says climate change may be a factor. The trend has been warming temperatures, and the rate of increase in over­night temperatures is double what it is for daytime highs.

As much as this research seems to be providing as many questions as answers, it does emphasize that producers have a legitimate concern about maturity, and Bullock’s advice to growers is not to take a CHU rating as perfect.

Yes, he says, you may know how many average CHUs to expect three years out of four, and the CHU rating on the variety.

“But if it says 2400 CHU on the rating, you know that you may need 200 or 300 CHU more to get that mature according to our research,” he says. “And I say may, because it’s variable; you might get it with 2400 but you might not. With corn there’s always going to be a risk… we’re just not there yet.”

Next steps

Lawley says the next step is to build on what the Corn Agronomy Project has provided so far and to further explore the economics and other benefits of corn in an overall crop plan.

“Western Canadian farmers are definitely interested in growing corn, and one of the reasons is they are looking to increase or maintain carbon in their soils and are excited about this source of carbon and the ability to protect the soil, because we’ve had a lot of soil erosion in the early spring over the past two years,” she says.

“There’s been a lot of positive interest from our work with strip till in our residue management experiment. We had farmers call us this spring who were interested in trying strip till on their farms, so we’ve got some preliminary new experiments where we’re growing corn in strips, and I think that’s an area we’ll be moving to next.”

This article was originally published in the September 2017 issue of the Corn Guide.

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