Is it time you get started with a cover crop?

Cover crops may not be as simple as we used to think. But they aren’t that complex either

The funny thing about implementing change is that it’s possible to over-think a situation and become mired in the process of simply getting started. A person becomes so concerned with the challenges of the “how” that they begin to lose sight of the value of the “why.”

In other words, getting started can be the hardest thing to do with something new, even though it’s also the most important.

Cover crops are a good example. It’s more than a matter of whether to grow a single-species cover. Some farmers have gone that route and are frustrated by stand issues with red clover after winter wheat. But just because one single-species option doesn’t fare well doesn’t mean there aren’t other options, or that multi-species blends are always better.

For Jake Munroe, what’s important first and foremost is that growers determine what’s best for them and their operations. Should farmers be investing in cover crops? Absolutely, he says. But it’s always a matter of taking the “one-step-at-a-time” approach.

“It’s a case of an individual grower figuring out what makes sense on their operation and what level of challenge or risk they’re willing to accept in taking on that new practice,” says Munroe, field crops soil fertility specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). “Then they can find something simple to start with and build confidence from there.”

Munroe acknowledges the move from the more traditional red-clover-into-winter-wheat standard, agreeing there are those who’ve found a lack of consistency with red clover. In spite of research findings from scientists Bill Deen and Dave Hooker of the University of Guelph that favour red clover, there’s a contingent of farmers who find the species exceedingly frustrating to manage. Instead, they’re trying oats or peas, or multi-species mixes, depending on what they’re looking for.

New fertility paradigm

Among some advisers and agronomists, there’s a growing sentiment that when cover crop blends get more complex, the likelihood that they will need fertilizer also increases.

That can inject a degree of doubt in the minds of potential cover crop users. Should you fertilizer first? But here again comes the benefit of “just getting started.” Munroe sees no clear indication of a “fertility first” requirement.

“You can have success growing a cover crop on lower soil-test soils and have a net positive effect because with red clover or another legume, you’re fixing nitrogen and adding it to the system and for the subsequent crop,” he says. “In cases where you’re growing a non-legume, you’re not having a detrimental effect, unless you’re harvesting it and that needs to be considered in terms of nutrient management and managing soil fertility.”

All of the old clichés apply about cover crops. They’re another tool in the farmer’s toolbox and it takes time to find the fit that creates the most value for your specific farm. And they aren’t a silver bullet.

“Growing a cover crop is not going to automatically increase soil fertility levels,” says Munroe. “With the exception of legumes, you’re not actually adding nutrients to the soil. Instead, you might be helping to scavenge some nutrients left over from the previous crop and help reduce the amount that leaches below the root zone. Depending on the crop and seeding date and amount of growth, you might be helping to capture nutrients from deeper in the subsoil and bring them to the topsoil. You will fix carbon and add organic matter and easily available sugars for soil life, which in time can help to enhance soil structure and rooting access and nutrient cycling, and how well residue is broken down.”

Some growers are getting ahead of themselves, and it’s important not to forget about the fundamentals when adopting any new practice. In Munroe’s view, the fundamentals to a cropping rotation call for diversity, including forages (when possible) and winter wheat as a regular part of the rotation. Another consideration is to look for ways to maintain soil fertility and soil organic matter.

There’s also an added layer of complexity with cover crops in the use of nutrient sources including manure or organic amendments. Some of the nutrients from those sources can be taken up very rapidly in cover crop biomass and held in a form that protects against loss. Munroe states there are growers who plant a cover crop and then build on the fertility, and plenty who address the fertility without adding cover crops at all. But he believes they’re missing out on some benefits from including cover crops in their rotation. Conversely, there are growers who are expecting a lot from their cover crops in terms of adding nutrients.

Ongoing research makes red clover’s impact hard to debate, yet frustration in growing it remains, tempting farmers try something different. photo: Supplied

Researching the impact

Although there’s a wealth of long-term research on the effects of red clover on subsequent corn yields (by Hooker and Deen with the University of Guelph), Munroe emphasizes that Ontario’s agri-food sector is still in its early days with long-term research on other cover crop options. Some growers want to see some type of research data on those. There’s also the argument about cyclically low commodity prices and tightening margins, and the question of whether a grower can really afford to grow cover crops, particularly if more fertilizer is needed for more complex blends.

“The other approach is to look at it from the perspective of ‘Can I afford not to?’” says Munroe. “In that case, you either look at some of the challenges in the situation, and — say, if there’s soil erosion that’s visible in the field, cover crops can be a real tool to help minimize that.”

The erosion aspect has been a large part of the cover crop debate, particularly in the past three to five years. However, part of what complicates that assessment is the difficulty in establishing a definitive dollar value on a volume of soil. Research in the U.S. in 2014 tried to define a value attached to losses in “snirt” — snow and soil combined. However those numbers reflect dollars lost in N, P, and K, not an actual value per unit of soil lost. Munroe states there is a value to the clay particles deposited into the ditch by wind or water erosion but it’s a very difficult measurement, especially on an annual basis.

“Really, you need to look at the entire system in this way, looking at the rotation benefit from wheat, the non-nutrient benefit from organic amendments and that doesn’t happen within a one- or two-year time-frame,” Munroe adds. “We’re looking at five to 10 to 15 years.”

Agriculture is still in the process of understanding the complexity and multiple layers of soil interactions, whether it’s seed-to-soil, soil fertility issues, soil biology or interactions with herbicides and pests. Then there’s another layer when adding cover crops. Yet Munroe emphasizes that regardless of those complexities, keeping the soil covered and protected through the season — and having live roots growing and contributing to the crumb and granular structure in soil — is where a grower can make tangible improvements, such as more even emergence.

Three added considerations

As important as it is to get started in working with cover crops (once the decision is made and the comfort level is set), Munroe believes growers can do more with their choices by keeping three important aspects in mind:

1. A deeper understanding of the soil profile. Munroe advocates growers begin to look at their soils with a different understanding — beyond just six inches of topsoil where fertilizer and nutrient recommendations work well. Although the subsoil is “nutrient dilute,” it makes up considerable volumes.

“There isn’t a high nutrient concentration there, but there’s a lot of volume to access,” says Munroe. “When we’re talking about cover crops and soil fertility, one of the key things to wrap our heads around is what we can do to get access to some of the subsoil that we might not normally get to. And then bring those nutrients up to where they’re more accessible for the following crop.”

At the same time, it provides some preferential pathways for subsequent crops’ roots to follow and gain access, particularly to water in a dry summer.

2. Sometimes, agriculture doesn’t take full advantage of the synergies that come with applying manure or other organic amendments with cover crops. By doing that, Munroe says that we’re increasing the above- and below-ground biomass of the cover crop while capturing some of those nutrients, tying them up in the cover crop for a time and reducing the susceptibility of losses. Fix carbon dioxide and keep it in place with a crop that you’re not going to harvest and add it that way. Cover crops are certainly part of the ongoing trend in adding soil organic matter.

3. A general statement — nutrient uptake is more than just soil test levels and the 4Rs of nutrient application. Granted, they’re key pieces of information in practice, but over time there also has to be an accounting of those practices that improve soil structure and crop rooting, and provide greater access to soil nutrients.

“I understand that it can be more challenging because it’s less prescriptive to think in that way — it’s not a recipe,” concedes Munroe. “But if growers can think of what they can do to provide that crop root the best environment possible to access nutrients in the soil, that’s just going to improve the efficiency of nutrient uptake in our cropping systems.”

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Ralph Pearce

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