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Cover crop considerations

Having a goal and being realistic will help achieve cover crop success.


July 24, 2020
By Sponsored by Mix It Up, Bayer Crop Science

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Cover crops are a hot topic these days, and for good reason: the benefits can range from reduced soil erosion to weed suppression to improved soil organic matter. The tricky part can be figuring out where to start if cover crops are new to you.

Like many parts of the world, Canada has been exploring cover crops in agriculture for many years on both the farm and academic levels. Cover crop research in Eastern Canada started in 2004 with a team of researchers at the University of Guelph’s Ridgetown Campus, with many farmers incorporating the practice into their operations in the years following.

In Western Canada, cover crops are a growing trend, but little research has been done to date.  Yvonne Lawley, assistant professor of agronomy and cropping systems at the University of Manitoba, and PhD student Callum Morrison have been working on a Prairie cover cropping survey. According to the preliminary results from the first year of their survey, the cover crops used most commonly in Manitoba, Saskatchewan and Alberta are: oats, clover, pea, radish, hairy vetch, fall rye, phacelia, sweet clover, sunflower and sorghum.

By comparison, popular cover crop options for Ontario growers include Brassica crops like oilseed radish and oriental mustard, legumes (such as varieties of clover, alfalfa, pea and vetch) and several cereal options.

With so many choices, how do you choose the perfect cover crop? Identifying your goal is the first step, according to Anne Verhallen, soil management specialist, horticulture, with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA).

“It still comes back to some basics,” Verhallen says. “Once you know your goal it’s a little bit easier to choose.”

Verhallen notes the importance of balancing the risks and rewards, emphasizing that cover crops are not an easy cure-all and they do require management. It’s better to start small and simple. Having realistic expectations and recognizing the monetary and time costs involved in cover cropping will help farmers make the decision that is right for their situation.

“You have to consider the rules of agronomy don’t change just because it’s a cover crop,” Verhallen says. “Cover crops are not the panacea for everything – they are a crop and they need to be managed.”

Function of cover crop Best choices for cover crop (in Ontario)
Erosion protection (i.e. wind, water) Winter rye, winter wheat, ryegrass, (well established) spring barley, oats
Nitrogen production Red clover, peas, vetch
Nitrogen scavenging Fall uptake: radish and other Brassicas, oats

Winter/spring uptake: rye, winter wheat

Weed suppression Radish and other Brassicas, winter rye, buckwheat
Nematode suppression

(Note: these are variety- and nematode-specific)

Cutlass mustard

Sudan/sorghums: Sordan 79, Trudan 8

Pearl millet: CFPM 101

Marigold: Crackerjack, Creole

Radish: Adagio, Colonel

Soil structure building Oats, overwintered winter rye
Compaction-busting Alfalfa, sweet clover
Biomass return to the soil Fall: oats, radish

Summer: millet, sorghum, sudan

Table courtesy of Anne Verhallen, OMAFRA.

Soil erosion from water and wind

Verhallen says a cover crop can contribute to a reduction in soil erosion. Discussing a study on phosphorus (P) runoff conducted by the Upper Thames River Conservation Authority, based in London, Ont., she notes, “[Runoff P concentrations] were reduced by up to 80 per cent using the cover crop. And, of course, this changes depending on what your soil topography is. Gentle slopes – not as big a deal; steeper slopes – a huge deal.”

Erosion doesn’t have to result in gullies in a field for it to have a serious impact. “It doesn’t take a lot to lose a fair bit of soil,” Verhallen adds. “Even sheet erosion – where it’s basically taking the thickness of a paper sheet each year – starts to add up.”

Grazing or forage feed

To demonstrate the value of using cover crops for livestock feed, Verhallen points to Mike Buis of Buis Beef in Chatham, Ont. Buis plants cover crops on the majority of his 700 acres, using rye, oats and winter wheat, depending on the other crops included in the field’s rotation. His cattle graze the fields from fall to spring, which has lowered his feed costs while improving the health of his herd, the soil and – occasionally – crop yield. According to Buis, his use of cover crops provides a return of $60 per acre (not including the cost of seed) and reduces feed needs by 280 tonnes.

However, Verhallen quotes Buis, reminding others to be realistic about their operation. “At the end of the day cover crops have to make sense within the whole farm system, from the cost of seed to timely fall planting and spring management. If it doesn’t make sense, it won’t work.”

According to the first year of Lawley and Morrison’s survey, grazing is a major use for cover crops among survey participants in Manitoba, Saskatchewan and Alberta. Lawley says farmer respondents indicated the crops most commonly grown include a good balance of annual forage plant types: oats, pea, hairy vetch, clovers, radish and fall rye. Eastern Canada has seen similar relationships, with some cash crop farmers working with other livestock farmers to take advantage of the forage crop being grown for cover.

Compaction-busting

Breaking up compacted soil is another possible benefit to using cover crops, Verhallen says, noting deep-rooted crops, like sweet clover and alfalfa, that will grow over time are good options.

“Radish also gets tagged as a compaction-buster, and it will – to a point. But if the soil is dry and hard, or if the compaction is severe, radish is just not going to do it.

“You’ve got to be realistic. Radish is only growing for a couple of months, whereas sweet clover and alfalfa – we know that those are long-term, lignified roots that have a whole couple of years to grow and make their way through every time there’s a little bit of a fracture or crack.”

Cover crop challenges

Including cover crops in a rotation can create other challenges, one of which is control.

“As you’re picking the cover crop, you’ve got to think about control,” Verhallen says. “There’s nothing more frustrating than having a beautiful cover crop and looking at it and going, ‘How am I going to get rid of that?’”

Methods of control include winterkill, tillage, herbicide burnoff or desiccation of the crop, and using a roller crimper or mowing the crop. Some cover crops are easier to terminate than others, and the method of control will often be determined by your goal in growing the cover crop and your specific situation.

“It’s very much where you are, and your soil type and what kind of equipment you’ve got. But you’ve got to consider what your options are for control.”

One major issue for farmers in Western Canada when choosing cover crops is canola disease, especially clubroot. While crop rotation and the use of cover crops can have significant benefits in controlling canola diseases, it’s important that the crops used aren’t susceptible to the diseases as well, as that will not reduce disease pressure. Including Brassicas as cover crops should depend on if or how frequently canola is grown in rotation. According to Lawley, “Some farmers are avoiding [Brassica crops altogether], while others who are less reliant on canola still seem to be using them.”

Farmers in Eastern Canada should be on the lookout for similar situations and avoid giving problematic pests, like nematodes, for example, a host to live off.

Know your growing conditions

One thing Verhallen notes is that, while much of the information she shared was fairly general and broadly applicable, her work is focused on Ontario and its growing conditions.

“Another caution I’d like to make is make sure, when you’re looking for information, that you’re evaluating that information based on your own growing conditions,” Verhallen says. She described the eye-opening experience of attending a North Dakota field day and seeing the greater amounts of light and space that get between their rows of corn, which allows North Dakota farmers to interseed corn and cover crops to reduce weed pressure.

“You never realize how differently things grow until you go somewhere else.”

For information on resistance management, visit www.mixitup.ca.