heresy? Shallow plowing once every seven years could help rather than hurt soil quality
It’s still possible to catch a glimpse of a moldboard plow now and then on the Prairies.
Usually, they can be seen rusting away peacefully in the bushes near an abandoned farmyard, or taking one last ride on the back of a scrap metal truck.
That’s where the older plows belong, said Pat Lynch, an independent certified crop adviser based in Ontario.
“Many of the older plows should be melted down into swords. They’d do less damage,” Lynch said in an interview.
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If that’s the case, why did he agree to moderate a demonstration of proper plowing techniques with modern, updated equipment at the recent Outdoor Farm Show in Woodstock, Ontario?
The demonstration was so controversial that at one point, Lynch says an extension agent from Ontario’s ministry of agriculture half-jokingly threatened to chain himself to the plow in protest.
But Lynch went ahead anyway for two reasons. First, many eastern farmers still use moldboard plows routinely, and he wanted to show them how to plow shallow, and secondly, to point out specific cases in which it might be a good idea. Older tractor plows typically use a 16-inch share measured across its width. In most cases, that means they only work well at about an eight-inch depth.
“We don’t have eight inches of topsoil that we can plow,” he said, adding that optimum depth to avoid bringing up subsoil is about four inches. To measure the depth of the furrow, he advises placing one foot on the bottom and the other on the top, and checking the distance between the soles with a tape measure.
Hitting that sweet spot even with modern plows is tricky, he said, adding that most farmers would find that a disc or other vertical tillage tool would work better.
Tillage has become anathema to many with the advent of no-till. But Lynch believes that no-till doesn’t mean “never till.”
That may sound heretical, but he argues that responsible farming methods should be based on rotation of crops, chemicals, and even — gasp — tillage methods.
“I’m talking corn stalks and possibly alfalfa,” he said.
“I’m not sure about using moldboard plows on cereal ground in Western Canada. Vertical tillage tools do a pretty good job of incorporating residue into the top four to five inches. ”
Plowing and other tillage methods are all about managing the three kinds of organic matter in soil. These include the bulk proportion — “the 100-year-old stuff” which is well mixed in with the soil, and the 1-10 per cent fraction called the “raw” organic matter that is made up of this year’s and last year’s crop.
Mix it up
The third component, called “active” organic matter, could be up to 30 per cent of the total matter. It is especially valuable because it is made up of residues anywhere from three to 10 years old in the process of breaking down into plant-available nutrients.
“If you’re in continuous no till, that fraction just stays on the top of the ground,” said Lynch. “It should be mixed into the top six inches.”
Using a moldboard plow or other tillage tool once every seven years or so, could be just the ticket for incorporating all of the valuable nutrients into the top six inches. Also, he argues that plowing on that schedule wouldn’t destabilize the soil aggregates and leave it vulnerable to erosion.
Ideally, a field would be shallow plowed in fall, with one pass of secondary tillage in spring before planting to avoid “beating up” the soil.
Many farmers think that good plowing should leave no residue showing, just like in the plowing matches. But in Lynch’s opinion, having some trash poking out of the ground helps to reduce the risk of erosion. With the growth in corn acres across the western Prairies, he expects that more farmers will take tentative steps towards using tillage again.
“With lower commodity prices, we went to no till knowing that we were giving up a bit of yield but making more money,” he said.
“Now, with higher commodity prices, that extra yield that we get with tillage makes it worthwhile.”
Lynch was a firm proponent of no till as far back as the 1970s, and still believes that on many land types there is no other way of preserving the soil.
“But now, on some of that flat level ground, we can do some tillage,” said Lynch.
