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LL-Atlantic: Environmental and yield benefits of cover crops

May 10, 2023  By Agriculture and Agri-Food Canada

Judith Nyiraneza stands in a field of sorghum sudangrass at the AAFC Harrington Research Farm. Photos courtesy of Agriculture and Agri-Food Canada.

On Prince Edward Island, where weather is often unpredictable, one thing you can almost guarantee is a windy day. Surrounded by the Atlantic ocean, winds often whip across the island, which could have unintended effects on farm fields through soil erosion. Bare soil is highly susceptible to wind and water erosion from rain and melting events.

Over time, farms lose valuable topsoil that is rich in organic matter, making the soil less fertile and less resilient to extreme weather conditions. Additionally, bare and water-logged soils are also much more likely to have excess nitrogen leak or leach into groundwater or be lost as nitrous oxide, a greenhouse gas, to the atmosphere.

As farmers continue to focus their efforts on sustainability, for P.E.I., that means preserving soil health and water quality. This is why Living Lab – Atlantic, a four-year, collaborative innovation project on P.E.I. between researchers, farmers and other partners, tested cover cropping as a management practice to enhance soil health.

Simply put, a cover crop is a plant grown for the benefit of the soil, rather than to be harvested for food. With Living Lab – Atlantic, local farmers have been at the forefront of co-developing the practices and research activities they see as most beneficial, like cover crops. They have experienced first-hand the impact of planting cover crops in their fields and in real-time since 2019.

Judith Nyiraneza, a research scientist with Agriculture and Agri-Food Canada (AAFC), co-leads the cover crop activity that involves several farmers and other researchers, including P.E.I. Potato Board research and agronomy specialist Ryan Barrett and Brandon MacPhail from MacSull Farms Ltd.

“Cover crops offer many benefits like reducing soil erosion, gathering valuable nutrients into its roots, reducing soil diseases and acting as a good source of carbon, a key indicator of soil health.”

– Judith Nyiraneza, Agriculture and Agri-Food Canada

Nyiraneza, Barrett, MacPhail and other participating farmers recently completed Living Lab – Atlantic research activities that set out to “uncover” the ideal use of cover crops within potato cropping systems and how they can be planted several times throughout the year, with varying benefits to farmers and their soil.

At AAFC’s Harrington Research Farm, Nyiraneza studied full-season cover crops that are planted over an entire growing season then plowed into the soil in the fall, prior to planting a potato crop the following spring. She tested a broad range of crops, including grasses, legumes, and a mixture of legumes and grasses, and found that pearl millet returns the highest carbon input into the soil. Pearl millet and sorghum sudangrass were associated with lower risk of soil nitrate leaching and higher total potato yield.

In another study, Nyiraneza evaluated winter cover crops planted in early to mid-September prior to planting potatoes the following spring. She found that winter cover crops, such as winter rye or winter wheat, reduced both soil erosion and nitrate leaching. Not only do winter rye and winter wheat recover quickly in early spring, they can provide additional protection during snow melt when risk of soil erosion is very high. Plus, farmers can also harvest them as a second cash crop. If harvested, winter wheat yield ranged from 4.5 to 7.6 tons per hectare and winter rye ranged from 3.2 to 5.1 tons per hectare.

An on-farm research field covered in full season cover crops.

Barrett has spent the last four years working with farmers, like MacPhail, across the island to study fall-seeded cover crops. These cover crops are planted after harvest of a cash crop or after tillage to prepare for next year’s crop. They include common grain crops like barley or oats, as well as newer crops to P.E.I. like daikon radish. MacPhail and other participating farmers contributed to cover crop testing and research by supplying the land, seed, equipment, time and staff to undertake the crop management practice.

Along with researchers, they determined which crops to plant as cover, in which fields, and for which production crops to follow. Barrett used splash pans in cover crop fields to measure the soil’s vulnerability to be moved through erosion. Splash pans were introduced by Nyiraneza and tested in previous studies. They are a simple way to measure the soil particles splashed by raindrops. Nitrates in the soil were measured at different times throughout the fall, and soil health tests were performed before and after cover crops were grown.

The data that Barrett and participating farmers unearthed was a huge endorsement for cover crops. Over four years, he found a 25 to 30 per cent decrease in topsoil collected in the splash pans, even in fields that had the slightest emergence of cover crops – solidifying their potential to reduce soil erosion. There was also a 30 to 40 per cent reduction in soil nitrate amounts in the root zone where cover crops were planted. The cover crop is sequestering those nitrates and preventing them from leaching into groundwater and waterways.

Cover crops not only have farmers seeing green in their fields for most of the year, they are also putting more green in their wallets. In the year following a fall cover crop, participants saw a 10 per cent yield improvement in the potato crop averaged across more than 20 fields loaned by farmers for this project. Ryan says a $25 to $50-per-acre investment in cover crops could lead to a more than $500 per acre return on investment from increased potato yields, according to these results.

Nyiraneza, Barrett and MacPhail now see fall-seeded cover crop adoption as a “no-brainer” and “win-win” for farmers.

“Seeing the results of Living Lab – Atlantic research take place directly through our production methods, on our fields is, to put it simply, ‘the best type of research.’ The cover crop research in our own fields, by our own means, gave our farm confidence that this method was quite beneficial across the board. As a result, other farmers now see strong trends that cover crops are worth the time and investment for our farms and for our communities.”

– Brandon MacPhail, MacSull Farms Ltd.

Other farmers on P.E.I. are getting on board with the trend. The ability to farm more sustainably while boosting yields is what makes cover crops so enticing to potato farmers on the Island. At the start of Living Lab – Atlantic in 2019, less than 24 per cent of potato acres were planted with cover crops in the fall before planting potatoes. According to P.E.I. Potato Board statistics, by the end of 2022, that number doubled to nearly 50 per cent and is expected to grow through Living Lab – Atlantic-led peer-to-peer knowledge transfer as well as funding available to farmers through AAFC’s On-Farm Climate Action Fund.

Barrett believes that P.E.I. is not an isolated case when it comes to fall season, winter fall and winter cover crop adoption and hopes that the team’s findings and knowledge transfer activities encourage more producers across Canada to adopt this practice.

“Every region is a little different, but these cover crop methods are definitely applicable to most potato-growing provinces across Canada. Grain and oilseed farmers also have lots of opportunities and time to plant cover crops in the fall after harvest. There is certainly room for growth, along with evaluation in different regions, according to their local climate and production practices.”

– Ryan Barrett, P.E.I. Potato Board

Nyiraneza notes that reducing rates of erosion for agriculture is one of the best things for farmers to do for their field. Over the long-term, it holds on to valuable top soil and increases soil organic matter while also increasing potato yields. However, the work on cover crops isn’t finished. Agricultural Climate Solutions will study cover crops’ potential to reduce greenhouse gas emissions as Canada continues to work towards net-zero emissions by 2040.

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