Hairy vetch cover crops provide mulch, control weeds

The key to organic rotational no-till lies in the amount of mulch cover, said a research technician.

The key is also understanding that tillage will be necessary at some point to control weeds, said Keith Bamford of the Faculty of Agricultural and Food Sciences at the University of Manitoba.

Since 2007, Bamford has been studying organic no-till using in-field methods in Manitoba that look at weed control, equipment, crop nutrition, crop rotation and agronomy.

Similar to conventional no-till, the goal of organic no-till is to reduce soil erosion, and soil moisture loss (after mulch is formed), improving biological activity, preserving organic matter, improving soil physical properties and reducing energy costs.

Bamford’s research uses a hairy vetch system to control weeds and 4,000 to 6,500 pounds of dry matter biomass is needed per acre in the spring. That same amount of cover crop biomass would double in the fall.

“Those are pretty big numbers to have growing out in the field,” he said.

Controlling perennial weed control in a rotational no-till is different from what is generally used on the Prairies in terms of organic perennial weed control.

“It’s that idea of doing that perennial weed control in the spring and then turning around and growing a mulch on that material at the end of the summer. That’s not something we’ve done in a zero-till setting and it’s not something that’s been done in research on the Prairies.”

“So it’s not a giant leap to think that we can grow some really heavy mulches on top of that type of control and get some Canada thistle control,” he said.

It’s also important to use suitable hairy vetches that are true winter annuals (planted in August to produce seed the next year).

“There’s a danger of planting hairy vetches that are closer to being annuals in our climate than winter annuals.”

“If we plant hairy vetch that starts to behave as an annual, we will have a problem very quickly because our hairy vetch will become a weed,” he said.

Managing mulches is necessary so there’s enough to seed into or at the very least covering soil over winter.

Keith Bamford models a hairy vetch and barley mulch beard pulled from between the rows in a no-till flax field. The mulch had been grown the summer before the flax crop was planted. | Anne Kirk photo

“It’s really about managing the mulch as much as anything because you can then take those principles and apply them against any number of other things that you would want to grow,” he said.

“Every farmer is going to have to look at this and go, ‘How am I going to produce that mulch or how am I going to incorporate some of those techniques into a system that will at the very least allow me to do less tillage out in the field?’ ”

The blade roller proved to be an effective tool during his research on practising zero-till organic farming.

“It allows you to essentially stop the growth of the mulch or control the growth of the mulch,” he said.

He said no-till should be rotated through the system and recommends trying a short-term scenario of 15 to 16 months verses a long-term commitment to zero till.

Using that 15- to 16-month cycle, he plants hairy vetch and barley in the spring and lets the hairy vetch grow in a vegetative state so it doesn’t sour or go to seed and grows all summer.

“With the blade roller, we’re rolling down the barley, we stop that growth and/or kill the barley before it sets seed and then we let the hairy vetch continue growing. Rolling does not kill the hairy vetch,” he said.

But producers must decide what benefit they’re after from their mulches and if they’re gradually managing them using the roller to achieve zero till.

Seeding early is another factor to make the most of the dead mulch and reduce weeds.

Katherine Stanley, left, Amie Bartley and Keith Bamford use a plot seeder to seed oat/pea green manure plots at Carman in early May. | Joanne Thiessen-Martens photo

“It’s the idea that we plant a crop as early as possible so it occupies that space where weeds would otherwise grow. It’s as simple as that,” he said.

No-till should also be part of a green manure year because it’s an opportunity to grow as much mulch as possible.

“It’s important partly because it’s an opportunity to grow the amount of mulches we want. It gives us a choice of a whole bunch of different green manure species that we wouldn’t normally grow in a crop production year. This allows us to focus on managing that green manure towards producing a mulch,” he said.

However, while no-till saves time and energy, tillage is still necessary at times to control weeds in organic agriculture.

“It’s one of our main methods for controlling weeds. Even if we were to grow enough annual crops to take the place of annual weeds, perennials are still going to become a problem. Nature is always going to go down that succession road one way or the other and probably growing annuals is part way down that road. The next step is to grow winter annuals and things like thistles or perennial grasses followed by trees if you have enough moisture,” he said.

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