Researchers praise the many benefits of cover crops

University of Manitoba plant science researcher says farmers need to think more about what happens below a field’s surface and how they can improve soil health

It’s time for farmers to stop treating soil like dirt.

“The role of a farmer is to manage a complex ecosystem to produce food, feed, fibre and fuel,” University of Manitoba plant science researcher Yvonne Lawley said at the recent Ecological and Organic Farming conference.

“Millions of ‘moving parts’ need to work together, both above and below ground. I want to challenge you to think about how what we do above ground is influencing what happens below ground.”

Lawley’s presentation was on cover crops, and she described them as multi-tasking wonders whose jobs include “keeping the soil covered, creating soil organic matter, fixing nitrogen, scavenging leftover nutrients, keeping live roots growing, creating food and habitat for soil micro-organisms, (and providing) residue management and weed management.”

Lawley paid special attention to one role — providing active carbon to soil health.

“Total soil organic carbon should have a large part passive carbon, which stays in the soil for a long time,” she said. “But active carbon, which breaks down readily, is also really important — it provides rapid cycling of carbon. Active carbon, also called bioavailable carbon, decomposes quickly and feeds soil micro-organisms.”

Winter cereals also boost levels of active carbon, as do plants with extensive root networks, such as perennial crops. Harvesting above-ground plant tissues also helps, she says.

“Make it a point to feed the soil, by decreasing the carbon-nitrogen ratio of cover crop residues, and leave plant residues to decompose in the field,” said Lawley.

Additionally, growers can increase soil porosity by growing more plants each year and for a longer part of the year, and by covering the soil surface to prevent crusting.

Reducing tillage

without glyphosate

Attendees were also told about research into using cover crops for weed control by agroecology student Kristen Podolsky.

Podolsky and her team conducted two projects, one on using hairy vetch as a green manure with no tillage, and another on using pea and barley green manure combined with reduced tillage.

In the first experiment, the crop was rolled to create a high-biomass mulch. It provided effective weed control, and resulted in good yields in the subsequent crops, flax and wheat, she said.

A variety of methods was employed in the reduced tillage experiment, including rolling, mowing and undercutting with a wide-blade cultivator.

“Every time you eliminate a tillage pass, you’ll have more residue,” said Podolsky. “When we completely eliminate tillage we have reduced nitrogen ability and greater weed pressure.”

While hairy vetch provided adequate biomass for mulch without tillage, the pea-barley cover crop was slightly less effective.

“The answer to whether we can reduce tillage without glyphosate is yes — you can eliminate tillage with hairy vetch as a cover crop,” said Podolsky, but adding “you can only reduce, not eliminate, tillage with pea-barley.”

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