Features Agronomy Fertility and Nutrients
The smell of success: manure and high-residue cover crops can boost potato yields, improve soil health

When crops are harvested, they can leave materials in the soil called crop residue. This residue, if incorporated into the soil, can increase the next crop’s yield, and can store more carbon in soil which helps reduce greenhouse gas emissions. Some crops, such as potatoes, leave lower crop residue in soils after they are harvested. As a result, farmers are looking for ways to improve soil health after harvest which can help improve yields in the following crop year.

Manure and cover crops benefit soil health

Agriculture and Agri-Food Canada (AAFC) scientist, Dr. Judith Nyiraneza and her collaborators, are on a mission to help farmers on Prince Edward Island (PEI) increase organic matter in soils and increase potato yield. As co-lead scientist for AAFC’s former Living Lab — Atlantic project, Dr. Nyiraneza recently completed a 2-year study that investigated the use of cow manure mixed with straw and high-residue cover crops in potato production systems. Manure contains a range of nutrients, and if properly applied using a precision low emission applicator along with use of a cover crop, it improves soil structure and water holding capacity that can help plants to grow.

“On Prince Edward Island, manure is available at dairy farms, but most potato growers may not have access to it. We’re aware of its capabilities in improving soil health, and we wanted to see short-term effects of manure application at a moderate rate of 20 metric ton per hectare on potato yield.”

– Dr. Judith Nyiraneza, Research Scientist, Agriculture and Agri-Food Canada

Dr. Nyiraneza sees lots of potential with cow manure when it is added to soil during the planting of cover crops at least 1 year prior to potato planting season. Simply put, a cover crop is a plant grown for the benefit of the soil, rather than to be harvested for food. With recommendations from Living Lab — Atlantic partners including the PEI Potato Board, Dr. Nyiraneza planted numerous field plots and treatments at the Harrington Research Farm that reflected the fields of Prince Edward Island farmers. Incorporating manure into cover crops increased total potato yield by a whopping 28%. With results like this, potato growers who have access to manure will be encouraged to incorporate it into their fields and that could spell good news for cattle farmers. This research is also encouraging producers to adopt mixed farming by integrating livestock production into horticulture fields as well as encouraging potato producers to partner with neighbouring cattle producers to access manure or to have cattle forage in rotational crop fields as part of the new Living Lab – Prince Edward Island.

Super cover crops and looking to the future

While manure may not yet be widely applied in potato production systems, cover crops planted in summer or in fall are gaining popularity on Prince Edward Island due to their ability to provide crop residue and nutrients into the soil for subsequent crops, reduce pests as well as reduce the risk of eroding healthy top soils. Cover crops planted in fall reduce nitrate leaching into waterways, keeping our water clean. As crop residues in soil are lower following potato harvest, Dr. Nyiraneza and her team set out to increase residues by studying eight different cover crops with manure applied and how they impacted potato yield, soil health, soil diseases and nitrate leaching. The cover crops were planted in the spring at least 1 year prior to potato planting season. The research team learned that pearl millet and sorghum Sudan grass were most effective in increasing potato yield and reducing levels of root-lesion nematodes, microscopic worm-like organisms that target roots causing yield loss.

“Pearl millet is a relatively new cover crop for Prince Edward Island, but it is showing great promise in returning high amount of residues in the soil, reducing the risk of nitrate leaching in soil, and increasing potato yield.”

– Dr. Judith Nyiraneza, Research Scientist, Agriculture and Agri-Food Canada

An ancient cereal, millet is considered a super grain. It’s climate resilient and sustainable crop, able to withstand short growing seasons, poor soils, and environmental stress, with low fertilizer and irrigation needs. This versatility also makes millet an excellent forage or cover crop, and it even shows promise as an effective biofuel.

With stats like these, it’s no wonder the Food and Agriculture Organization of the United Nations declared 2023 the International Year of Millets.

Now with the launch of the new Living Lab — Prince Edward Island, Dr. Nyiraneza is continuing her work on manure and its effect on greenhouse gas emissions and ability to store carbon. Starting in 2024, she is working with Prince Edward Island farmers to further develop and trial various liquid manure application methods including broadcasting manure onto soil, injecting it into the soil and mixing it with a natural organic substance called biochar.

While Dr. Nyiraneza is continuing to solidify her data, it already appears that cover crops mixed with manure can provide a good one-two punch for farmers looking to improve soil health and boost potato yield. Just don’t mind the smell!

Key discoveries/benefits

• With input from project partners, scientists at AAFC on Prince Edward Island investigated the use of cow manure mixed with straw and high-residue cover crops in potato production systems to increase soil health, yields and environmental benefits.
• Manure incorporated with cover crop planting at least 1 year prior to potato planting season, increased total potato yield by 28%.
• Pearl millet and sorghum Sudan grass cover crops were most effective in reducing nitrate leaching in soils, increasing potato yield and reducing levels of root-lesion nematodes, microscopic worm-like organisms that target roots causing yield loss.
• Dr. Nyiraneza is continuing her work on manure and its effect on greenhouse gas emissions and ability to store carbon. Starting in 2024, she is working with Prince Edward Island farmers to further develop and trial various liquid manure application methods including broadcasting manure onto soil, injecting it into the soil and mixing it with a natural organic substance called biochar.