A wet cycle has caused some farmers to rethink zero till

Seeding & Tillage Focus: As the province’s wet cycle appears poised to break, soil compaction is a lingering after-effect

The past few years have been a bit hard on zero till in Manitoba.

Faced with a flood followed by a long wet cycle, more and more farmers in the southwest part of the province were forced to do something they thought they’d left in the past — pull out their tillage implements.

Their aim, says provincial land management specialist and tillage expert Marla Riekman, was to open up the land and warm it and dry it. While some worry this won’t augur well for the long-term success of zero till, it’s not clear farmers are moving away from the system.

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“It’s a bit hard to get a read on whether it has been happening because farmers are less interested in zero till, or because they were facing such severe moisture conditions,” Riekman said in a recent interview. “There was an extremely wet cycle following the flood, and their land never really dried out.”

The best way to dry a wet soil is to have a plant growing in it, of course, but barring leaving the weeds to grow, most farmers struggled with the art of the possible during this wet cycle, mudding in crops to keep the doors open and the bills paid.

Hardpan a risk

One problem that’s hit the radar for a lot of growers as a result of this wet period is hardpan.

The perennially wet soils forced them to sow crops and perform other field operations in less-than-ideal conditions which in turn raised the risk of compaction, Riekman said.

“They were forced to plant their crops and perform other field operations when their fields were wet. When that happens, you have a high risk of compaction.”

That process happens exactly as you would expect. Big equipment — and getting bigger and heavier with each passing season — meets wet soil, damaging the soil structure. Soil particles are pressed closer and closer together with each pass of the equipment under these conditions, eliminating the pore spaces that give soil many of its productive properties.

Suddenly water doesn’t infiltrate the soil as well and doesn’t drain like it once did, especially when it’s saturated with moisture. The exchange of gases grinds ever slower, leading to lack of air for plant roots. Compaction also increases the soil strength, which can be good if you’re building a road, but not if you’re a fragile wheat seedling that needs to punch roots down through it to access moisture and nutrients.

Riekman said it’s fairly obvious there is potential for yield reduction, but “how big the impact is on yield we don’t necessarily know.”

Nathan Gregg, an applied agriculture project manager for the Prairie Agriculture Machinery Institute (PAMI), said there’s also another secondary type of ‘compaction’ that’s a bit more common in Western Canada. It used to be called ‘plow pan,’ now it’s more commonly known as ‘tillage pan.’

“What happens here is that your tillage device moves horizontally through a wet soil and you get a shearing and smearing effect,” Gregg said.

Over time a similar crusted layer will build up a couple of inches below the soil surface, with the key difference that it doesn’t tend to extend for many inches and even feet down through the soil profile. The problem is especially likely where growers are performing field operations to the same depth repeatedly, in wet conditions, and the risk rises when the tillage devices cover more ground.

“The relative risk is lower with a narrow opener, for example, versus say a 12-inch sweep, Gregg said. “Proportionally, the larger tillage tool is covering a larger part of the field with each pass.”

Regardless the source of the problem, he said the end result is similar for growers.

Vertical tillage

Some growers are looking to combat the problem with vertical tillage, but here Riekman says there’s a lot of variability in what people define as “vertical tillage.”

There are shallow vertical tillage implements with rows of vertically mounted coulters designed to slice residue and penetrate the top layer of soil without inverting it.

Other more aggressive versions have angled gangs of coulters and other types of blades which disturb the soil far more, especially as most are designed to be operated at relatively high speeds of seven to 10 miles an hour.

“Some of these implements move quite a bit of soil, almost as much as a double disc in some cases,” Riekman said.

There are a few new types of vertical tillage implements that are fresh on the market and which cut deeper and act almost as a soil aerator. They might play a role in helping with compaction at the six- to 10-inch depth, but most of the others are only going down a couple of inches, maybe four inches at the most, and seem to have a better fit managing crop residue than fixing hardpan problems.

PAMI’s Gregg agreed that there is significant confusion over what vertical tillage really is, and almost all the implements called vertical tillage don’t truly fit that category.

“A true vertical tillage unit cuts the soil deeply, several inches down, causing cracking and fracturing outwards and downwards,” he said. “It does this without inverting the soil. Almost none of the equipment people are calling vertical tillage does this. Really there are only a couple on the market in Canada — Salford has one, for example.”

Cover crops

One other option that might bear consideration is taking a page from North Dakota producers who have adopted cover crops that include species such as tillage radishes which can send large taproots down to break through the compacted layer. Riekman said the practice has become widespread in the southern part of that state for a number of reasons, but growers in the northern portion aren’t jumping aboard yet — if anything that trend is more pronounced on this side of the boundary.

“We’re a bit slow to adopt it here,” she said. “There is some research that’s happening in northern North Dakota that will likely have some applicability here though, so it might be worth watching for.”

In other parts of the province — especially the Red River Valley where more corn and soybeans are showing up — strip tillage is growing in popularity. Farmers are adopting this Corn Belt practice that sees a narrow band of tillage for row-crop applications, a band that’s shifted from year to year using RTK satellite positioning. This gives the benefits of tillage to the crop in the year of production, while leaving the rest of the field undisturbed.

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Gord Gilmour

Gord Gilmour is Editor of the Manitoba Co-operator.

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