For some, cover crops come from anything available to keep things green through the shoulder season. For others, they’re a carefully curated recipe to make specific improvements in a field.
The blend demonstrated in late July at the Melfort Crop Diagnostic School was closer to the second option.
A full season mix from southwestern Manitoba company Covers & Co., the 16 species included forage oats, forage barley, forage peas, yellow peas and smaller percentages of purple top turnip and spring triticale. It was intended as forage for haying or grazing.
“Diverse mixes like this are really great for forage production or soil health,” said Austin Baron, an agri-environmental specialist with the Saskatchewan agriculture department. “But it’s all dependent on what you want to do on your farm.”
Why it matters: Cover crops for both forage and grain systems are based on promised soil health benefits, crop nutrition and beneficial insect support.
Cover crop blends aren’t always straightforward. Speakers on the subject often stress that the design depends on the specific gains a producer seeks.
“I was always looking for how many species do I need to make this great. No one can ever give me a straight answer,” said Baron. “Which is too bad. I like a solid line, like ‘this’ is how many species you need.”
The general advice is to pick from different families such as brassicas, cereals and legumes, based on what is known to grow well in an area, but some options provide little benefit when included in a cover.
For example, Baron questions inclusion of flax or sunflowers. There are better feed options with better roots and, in the case of sunflowers, less problematic residue. However, she acknowledged that sunflowers are powerful pollinator attractants.
For crop production, she recommends a simple intercrop mixture of two or three species, such as oats and peas, to ensure easier cleaning. If the goal is soil health and forage stand production, a greater plant diversity is better.
“Lots of our brassica species, like turnips and radishes, have a really strong taproot or tuberous root and they can get down into those deeper layers and open up that soil and really help with that water infiltration,” she said. “So having different rooting systems in there really allows for different channels of water to penetrate your soil horizons.”
Biomass and soil organic matter gains are also possible compared to monoculture crops.
“We saw … a significant gain in the organic matter content at the five to 20 centimetre depth over only two years,” said Jeff Schoenau, a Saskatchewan government soil scientist and strategic research program chair in soil nutrient management.
“By the time it dries down, you may not see a really impressive dry matter yield. But below ground, if you’re looking for improvement in the soil health, I think that’s where these kinds of polycrop systems, as a cover crop, are really going to come in, especially when they’re grazed or hayed and then swath grazed.”
Cover crops have also gained attention for their potential to include nitrogen-fixing crops, potentially lowering fertilizer requirements. Most nitrogen from a legume-heavy cover crop is released the following year from old root nodules, Schoenau said.
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