Green cover crop plots from the long-term experiment in Ridgetown

Inderjot Chahal, Richard J. Vyn, Danielle Mayers, and Laura Van Eerd. 2020. Cumulative impact of cover crops on soil carbon sequestration and profitability in a temperate humid climate. Scientific Reports. doi:10.1038/s41598-020-70224-6
Research summary by Inderjot Chahal

key messages

  • Surface soil carbon storage was 11 to 22% greater with cover crops than without after 9 years
  • Cover crops improved profit margins in vegetable crop production, but not grain or oilseed production
  • A carbon trading price of $50 per tonne of carbon could offset losses and improve adoption of cover cropping in grain and oilseed cropping systems

While cover cropping is a promising option for increasing soil carbon storage in the long-term, the economic return on cover crops in cropping systems is understudied. Beyond soil carbon storage, another concept which has gained global attention is “carbon trading”. Carbon trading provides financial incentives to practitioners through a market for carbon storage in the soil. Paying farmers for soil carbon storage encourages them to invest in sequestration strategies. A carbon pricing policy exists in Canada; however, a mechanism for compensating farmers is lacking. Therefore, this study was conducted at University of Guelph, Ridgetown Campus, to evaluate the long-term effect of cover cropping on soil carbon storage and economic benefits in a mixed vegetable-grain-oilseed cropping system.

What they found

Results indicated that surface soil organic carbon content was 11 to 22% greater after using annual cover crops 6 times over 8 years than when no cover crops were grown. The amount of surface soil carbon stored with cover crops was 10 to 20 tonnes of carbon per hectare, depending on the species, and was related to the amount of above-ground cover crop biomass. For instance, because oat dies over the winter, it had the least annual above-ground biomass and carbon inputs, and so contributed the least to carbon storage. A mixture of oilseed radish and cereal rye contributed the most to carbon storage, with the most above-ground biomass and carbon inputs.

Profit margins in processing vegetables increased with an oilseed radish cover crop, or a mixture of radish and cereal rye by 5-9% compared to no cover crop use. But in grain and oilseed crops, profit margins decreased by 1-10% with cover crops. This is likely a major barrier in adoption of cover cropping by grain and oilseed producers. With a carbon trading price of $50 per tonne of carbon, the profit margins for including cover crops in grain and oilseed cropping systems were greater than having no cover crop.

Why it matters

Regardless of carbon trading, profit margins were consistently greater with cover crops than without in vegetables cropping systems. A payment of $50 per tonne of carbon is likely needed to encourage cover crop adoption and offset losses in grain and oilseed production systems with cover crop usage. To our knowledge, this is the first report on economic returns from cover cropping with carbon pricing for surface soil carbon storage.

How they did it

This study took place on a long-term cover crop experiment established in 2007 at University of Guelph, Ridgetown Campus. To measure changes in soil organic carbon content, surface soil (0-15 cm) was sampled from each plot in September 2015 and 2016 (after processing tomato harvest). Profit margins were calculated using commodity sale prices and costs of cover crop seed, custom planting, herbicide product and application cost. Costs included in the analysis were conservative and might have resulted in over estimation of actual expense incurred by the growers. Researchers compared the profit margins from cover crops with the control. Additionally, economic returns from cover crops were evaluated at carbon pricing of $20 carbon per tonne (existing carbon price in 2019) and $50 carbon per tonne (projected price for 2022) to account for the soil carbon stored with cover crop usage.

This project is funded in part by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), through the Ontario Agri-Food Innovation Alliance. The Ridgetown Campus is one of 15 Research Stations owned by the Agricultural Research Institute of Ontario and managed by the University of Guelph through the Ontario Agri-Food Innovation Alliance, a collaboration between the Ontario Government and the University of Guelph.

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