Cover crops help reverse soil organic matter loss

The benefits may not show up immediately so farmers need to be patient

In Ontario, where the loss of soil organic matter is a long-standing problem, cover crops and other cultivation strategies designed to improve soil structure are playing an increasingly important role in cropland sustainability.

However, a variety of factors are limiting how quickly Ontario farmers are adopting cover crops, even as soil organic matter in the province continues to decline, albeit more slowly than in previous decades, and with rates varying from county to county.

Still, experts say improvements in extension and a growing understanding of cover crop management are bringing ever-more opportunities for soil improvement.

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Why it matters: Average soil organic matter levels continue to decline across much of Ontario. That decline can be reversed through more active soil management, diverse crop rotations, organic amendments, and cover crops. The key for the latter, however, is to start slow.

Making an intensive cover crop system work

Blake Vince, a Merlin-area grain farmer, has been incorporating multi-species cover crop mixtures in a no-till system since 2011. He plants into living greenery each spring — a handful of the species within his 18-species seed mixture can successfully overwinter — using a standard seed drill modified to cut through the cover crop. The remaining cover is treated with herbicide.

The system is designed to mimic the natural diversity of wild plants and one that he says improves the overall health of his soil.

Blake Vince uses cover crop mixtures as part of his no-till farming system.
photo: Mel Luymes

“We are really starting to see the system come to life in terms of the resilience of our crops in subsequent crop years,” says Vince.

“We’ve seen a proliferation of beneficial insects. We have slugs like everyone else, but most times it’s not an issue because of all those beneficial insects…. There’s been an increase in rare or endangered species like the bobolink and meadowlark.”

Vince says the decomposition rate in his fields has skyrocketed, meaning he’s seeing a much higher level of microbial activity. He also says he’s seen noticeable improvements in water and nutrient uptake, carbon sequestering and significantly more consistent crop growth, at least in normal years.

“Our ultimate observation is we’re seeing a huge improvement in water infiltration.”

However, Vince has also experienced setbacks. Near-drought conditions in the past two summers and wet spring planting conditions caused less-than-ideal corn yields, although he was able to harvest a decent crop despite those issues.

He also noticed large swings in yields in adjacent rows of the hybrids he had planted. He believes this happened because those hybrids were not genetically designed with intensive cover cropping systems in mind.

Jake Munroe, field crop soil fertility specialist for the Ontario Ministry of Agriculture, Food and Rural Affairs, says the perception that cover crops hurt yield can prevent farmers who work with tight margins from considering them, largely because there is usually no immediate payback. Perceptions of other risks, such as producing too much surface residue, also serve as barriers to more widespread cover crop adoption.

As well, farmers may not see the need for drastic changes to soil management, if they lack awareness of organic matter decline.

“Organic matter decline is one of those things that kind of creeps up on you. People get used to how soils perform regardless of its state…. Once you’re used to crusting, you just start to deal with it,” says Munroe. “Short-term rental situations are not conducive to long-term soil strategies.”

Adding fertilizer in a strip till system.
photo: OMAFRA

Munroe emphasizes that cover crops can address soil management challenges ranging from low organic matter to compaction and soil erosion, when used alongside other sound management practices.

Starting slow

While Vince continues to make his 18-species cover crop system work, both he and Munroe say those interested in cover crops should start slow.

Munroe says growers can start with one or a simple mixture of cover crops seeded after winter wheat. This could include oats, peas, or radishes; such plants do not overwinter, and so are easier to manage in spring.

“For those who have success with underseeded red clover in winter wheat, it is still an excellent cover crop that can be killed in the fall or spring,” he says.

Ultimately, which cover crop is used is determined by the grower’s goals. If generating a nitrogen credit is the focus, legumes are the best option. Reducing erosion might require species that provide more winter cover. Reducing compaction could start with species that produce deep taproots or fibrous root systems, radishes and cereal rye, for example.

Those with greater cover crop experience, Munroe says, may want to add more species, such as sunflowers, warm-season grasses like sorghum-sudangrass, or alternative legumes such as hairy vetch. They may also include species that can successfully overwinter, although he reiterates the importance of having a clear management plan to deal with the spring growth.

In addition, Vince adds that farmers interested in delving into cover crops do not have to spend large sums of money on equipment. He suggests modifying pre-existing equipment where required.

Other ways to build soil organic matter

Christine Brown, field crops sustainability specialist with the OMAFRA, says the ideal way to build soil organic matter is through a combination of cover crops and organic amendments such as manure.

In Ontario’s most southern counties, where livestock and manure are comparatively hard to find, other organic amendments such as digestate fertilizer can work.

Brown says work conducted by her and other colleagues showed a combination of digestate fertilizer and oats have the potential to increase organic matter by one per cent in 25 years, a substantial amount.

Applying livestock manure or digestate fertilizer are ways farmers can help build organic matter.
photo: OMAFRA

“Cover crops add organic matter. (Organic fertilizer) adds organic matter. It’s kind of a one-plus-one-equals-three thing. They have a synergy when used together,” she says.

Munroe adds that municipal compost and biosolids can also serve as a valuable source of organic material, particularly for grain fields that don’t receive manure. He also says producers should not underestimate the importance of soil microbial activity in building soil organic matter, and should use both cover crops and organic amendments, not to mention diversified crop rotations, to promote soil life.

Don’t judge success from the surface.

Roots are also more effective at building stable soil organic matter than green shoots, and Munroe encourages farmers to measure their cover crop’s worth by more than surface appearances.

Vince expresses a similar sentiment.

“As farmers, we are visual learners. So much of the detail of soil health requires our other senses and a microscope.

“The only thing we have to invest in is a change of attitude.”

About the author

Contributor

Matt is a freelance writer based between Essex County and Chatham-Kent. He is interested in all things scientific, as well as rock n' roll, hunting and history. He also works with his parents on their sixth-generation family farm.

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