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To till or not to till?

This past year, Ontario saw a huge swing away from no-till to conventional or minimal tillage, according to Horst Bohner, soybean specialist for Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). The problem? Maize residues are impacting soybean yields in the following year – or so producers believe.

In 2014, the province had a late fall, followed by a cold hard winter with little thawing, followed by a very dry spring. “That led to a tremendous amount of corn residue in the spring of 2015, and then on top of that, we had a frost on May 23, and if you have a lot of residue on the surface frost does a lot more damage,” Bohner says.

And as of 2015, “every other field is black in Perth County,” he says. “In Ontario, we’re very frustrated with corn residue and quickly going away from no-till.”

The cultural change has been underway for a number of years. Back in 2008, Bohner, in co-operation with the University of Guelph, was already analyzing different tillage and residue removal treatments. He’d observed that many growers were shifting back to intensive tillage due to the belief that maize residues hindered soybean performance. Bohner’s work interested Michael Vanhie, a masters student under the supervision of Bill Deen, an associate professor at the University of Guelph, who decided to focus his research on soybean response to the management of crop residues.

Over the course of two growing seasons, Vanhie – now a field development representative for DuPont – set up a field experiment in three commercial fields to test the response of soybeans to maize residue management.  

The experiment was set up to analyze three rates of removal: no removal, intermediate removal of residue (some residue, including stalks and leaves, removed), and nearly complete removal of residue (removal of as much residue as possible without disturbing the soil). The study involved 10 tillage systems and stalk chop treatments across all levels of residue removal.

The team also examined the effects of various planter types. They used a no-till planter drill in some subplot treatments, and a no-till row unit planter in others.

The results? Shallow fall and/or spring tillage did not result in higher soybean yields compared to no-till alone.

“The no-till system was one of the most competitive systems,” Vanhie says.

But there were other noteworthy results. For example, Vanhie’s team utilized a stalk chopper to try to speed decomposition of residues in one subplot treatment. When soybeans were planted using a drill planter in no-till fields after residues had been stalk-chopped, yields decreased.

“It resulted in more residue on the soil surface with a thicker mat. As you went through with the drill to plant, it wasn’t as capable of pushing the residue aside and there was a shallower seeding depth,” says Vanhie. When the row unit planter was used, however, there was no yield hit, as it was capable of manipulating the chopped mat of residue.

Year to year differences
Vanhie says that the benefits of zero tillage have been thoroughly documented; no-till results in reduced fossil fuel consumption and erosion. In most cases, he says, research has shown that no-till results in either higher yields or no yield reduction, meaning that growers usually see higher profits by using no-till.

“In our study, no-till yielded numerically better than most systems,” he says. “But there are many, many factors that affect yield – moisture, soil type and genetics, for example, and these can all have an impact on a yield response.”

Vanhie’s study involved medium-textured soils and moderate weather conditions. “When you see a no-till yield hit it is usually in a wet year where the soil is slow to warm up, and on heavy clay soils where you have poor drainage. That’s where you’d have a benefit to tilling the soil,” he says.

Bohner agrees. “How big of an issue corn residue is going to be is highly dependent on the growing season, and during those years of the project, the corn residue was not as big of an issue as we thought it might be.”

But the biggest influence on producers’ cultural practices is not research at all, but other producers’ opinions about what works.

“You can have all the research in the world to show that no-till works and yields just as much, but if there’s a feeling in the countryside that conventional tillage is more robust and yields better, people will go back to tillage wholesale and they don’t really count research as high on their list as what the neighbour is doing,” Bohner says.

OMAFRA’s recommendations are tailored to this reality. These days, OMAFRA recommends producers leave at least 30 per cent residues undisturbed on the soil surface to reduce the risk of erosion – in effect, reverting to minimal tillage instead of intensive tillage.

Bohner says residue management will be key in the years to come as corn residue biomass continues to increase. Corn yields are much higher than they were in the past, he says, while bean yields are relatively low. “Nobody wants soil erosion, and we all have to work on reducing that. One of the ways is minimal tillage versus plowing.

“You have to get a good crop, so some form of residue management is becoming more important in modern soybean
production.”