CFCRA Cropping Systems Cluster: Activity 4 – Cover crops and 4R strategies to mitigate GHG emissions

Objectives:

• Determine the impact of cover crops and combined urease & nitrification inhibitors under no-tillage and conservation tillage treatments from 6 sites (4 provinces) on growing-season nitrous oxide (N₂O) & carbon dioxide (CO₂) emissions over 4 years and on agronomic performance data, including nitrogen (N) uptake and corn yields over 5 years.
• Increase carbon sequestration and active carbon (C) fractions using cover crop and inhibitor treatments.
• Model the 24 site-years of data using the Canada DeNitrification-DeComposition (Canada DNDC) model and scale up to the provincial level in Manitoba (MB), Ontario (ON), Quebec (PQ), and New Brunswick (NB) to understand integrated agronomic and environmental impacts.
• Evaluate how the microbially-mediated C and N cycling processes that underpin soil health are altered by combined cover crop and inhibitor treatments.

Impacts:

• Increased N fertilizer availability to corn by reducing ammonia (NH₃) losses by over 90% and by reducing N₂O losses by at least 30%.
• Increased corn yields by at least 7-8% with improved cover crop and N management strategies including improved N placement and use of urease and nitrification inhibitors.
• Increased C sequestration with the improved management of cover crops and corn.
• Improved ability to predict the effect of nutrient management strategies on N losses and yields in MB, ON, PQ, and NB.
• Improved knowledge of the impacts of N placement, urease and nitrification inhibitors and cover crops on microbial activity of the representative soils from MB, ON, PQ, and NB.

Scientific Summary:

Two environmental challenges for Canadian agriculture are: 1) reduced carbon (C) inputs with annual cropping, and (2) environmental N losses, including nitrous oxide (N₂O) emissions, nitrate leaching, and ammonia (NH₃) volatilization associated with nitrogen (N) fertilization. Increased planting of soybean and less frequent growing of cereal and perennial forage have lowered soil organic C (SOC) levels in Canada. The need to reduce global and national greenhouse gas emissions requires finding ways to reduce direct (from soil) and indirect (from ammonia volatilization and leaching) N₂O emissions from fertilizer use by at least 30% by 2030. Corn is a major agricultural commodity in Canada with recent increases in yields and area planted. Nitrogen inputs are high relative to other crops and are expected to increase with genetic improvement, thus, it is important to find ways to improve N efficiency and reduce N losses without compromising farm profits. Cover cropping and 4R nutrient management are the most strategic technologies that can increase soil organic C, by increasing annual primary production and C capture while reducing N₂O emissions from fertilizer use. This project will investigate practices that both reduce N₂O emissions as well as enhance C sequestration and soil health in the major corn growing regions in Canada. There will be 8 core treatments evaluated in 6 regions (South Central Manitoba; Elora, ON; Woodslee, ON; Ste. Anne de Bellevue, QC; Quebec City, QC; and Fredericton, NB). These treatments include using a fall over-winter non-legume cover crop as well as a side-dress injected urea ammonium nitrate (UAN) fertilizer solution with combined urease and nitrification inhibitors. We propose to use a cereal rye cover crop following soybean harvest to add a cereal crop to the 2-year corn-soybean rotation and thereby provide additional C to the soil.

Experimental Approach: Each location will include both phases of a corn-soybean rotation (corn-field pea in MB). The soybean/pea field will have an over-wintering non-legume cereal rye cover crop planted in the designated plots following harvest. The cover crop biomass/N uptake will be measured in the spring and corn planted into the standing terminated cover crop. Gas samples will be collected from static chambers at a minimum of 30 times over the growing season and episodic and seasonal N₂O and CO₂ emissions determined. GHG measurements will start by May 1st and, where feasible, start earlier to capture spring thaw N₂O emissions before the cover crop is terminated in the spring. Corn emergence, above-ground biomass/N uptake and grain yields/N uptake will be measured on all 6 sites. Nitrogen fertilizers will be injected to reduce NH₃ volatilization in designated plots on all sites. Baseline soil C levels and stocks to 1 m depth will be collected and compared to C levels after 5 years to assess the C sequestration of each treatment. The data will be modelled using the Canada DNDC model. An overall agronomic and a modelling paper will be produced in addition to site-specific publications.

Benefits: Field crop producers will obtain information on the yield, soil health and environmental benefits of growing cover crops in a corn-based rotation. Cover crops and combined urease and nitrification inhibitors could increase crop yields by 7-8%, reduce GHG emissions by at least 30% and reduce NH₃ losses by 90%.

Farmland Impacted: At least 50% of the grain corn (1,420,000 ha), soybean (2,300,500 ha), and field (dry) pea (1,650,000 ha) acreages in Canada (based upon 2022 data) could benefit from these management practices.

External Funding Partners:

This activity was funded in part by the Government of Canada under the Sustainable Canadian Agricultural Partnership’s AgriScience Program, with industry support from the Canadian Field Crop Research Alliance (CFCRA) whose members include: Atlantic Grains Council; Producteurs de grains du Quebec; Grain Farmers of Ontario; Manitoba Corn Growers Association; Manitoba Pulse & Soybean Growers; Saskatchewan Pulse Growers; Prairie Oat Growers Association; SeCan; and FP Genetics. Funding support was also provided by Diageo.