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Evergreen farming in southern Ontario: more effective use of cover crops in rotations involving corn, soybean, or winter wheat

Principal Investigator: Xueming Yang and Dan Reynolds

Research Institution: Harrow Research and Development Centre, Agriculture and Agri-Food Canada (AAFC)

Timeline: April 2017 – June 2021


  • To develop recommendations for using cover crops in corn-soybean-winter wheat and corn-soybean rotations grown in medium and fine textured soils (e.g., Brookston clay loam) in the lower Great Lakes watershed. The specific project objectives include:
    • Determine the most suitable legume cover crops for seeding into wheat stubble after winter wheat harvest in summer.
    • Assess the amount of nitrogen accumulated in legume cover crop aboveground biomass.
    • Evaluate methods for cover crop termination, cover crop incorporation, and cover crop effects on root-zone-available nitrogen concentrations and corn yield.
    • Determine if there can be reductions in nitrogen fertilizer inputs for corn as a result of the cover crop “nitrogen (N) credit.”
    • Determine the impacts of cover crops on soil physical quality such as soil hardness, water storage and aeration and soil organic carbon content.


  • The successful communication of how to effectively integrate cover crops into field crop rotations will assist farmers in improving their stewardship of the land by increasing nutrient use efficiency and improving the soil’s resilience to water excesses (temporary flooding) or water deficits (droughts).
  • Successfully maintaining year-round soil cover may lead to measurable improvements in the water quality of the lower Great Lakes, which are critically important sources of water, fish and recreation for both Canada and the United States.
  • Successful incorporation of legume cover crops into soybean – winter wheat – corn rotations may significantly reduce corn dependence upon fertilizer N.
  • For heavy textured soil in southwestern Ontario, summer-seeding legume cover crops can accumulate substantial biomass N by late fall, and they are winter-hardy and regrow well in the following spring.
  • If fall termination of the cover crop is desired, summer-seeded hairy vetch or white/crimson clover mix are recommended because they accumulate more biomass relative to red clover. If strong spring re-growth is desired, clovers appear to be less desirable than hairy vetch because clovers tend to be more difficult to spray-kill in the spring and they can reduce grain yields by delaying corn emergence and reducing corn stands.
  • Hairy vetch can generate large amounts of biomass both in the fall and in the following spring. Hairy vetch is also easy to terminate, and it can reduce N fertilizer requirement by providing as much as 100 kg N ha-1 to a following corn crop.

Scientific Summary:

Soil and water quality in southwestern Ontario is important to maintain in order to achieve improvements in field crop yields, reduce sediment in streams and lakes, and limit appearance of dead zones and algal blooms in the lower Great Lakes, especially Lakes St. Clair, Erie, and Ontario. Water quality is of national and international importance because the Great Lakes represent about 20% of the world’s freshwater reserve, which is shared and relied upon by more than 40 million Canadians and Americans for drinking water, field crop irrigation, commercial and sport fishing, and general recreation. Agriculture has an acknowledged role in the soil and water quality of the Great Lakes watershed. Farmers recognize that intensive crop production systems can lead to the degradation of the soil by decreasing soil structure, permeability, and soil organic carbon content. Cover crops may play an important role in maintaining soil health and can influence carbon and nitrogen stores. Although there are many anticipated agronomic, economic, and environmental benefits to using cover crops, they can be difficult to implement in crop rotations with long-season crops such as corn and soybean as there are not sufficient growing degree days left in the fall for successful establishment when the cover crop is planted after harvest. Preliminary work on a sandy soil suggested that seeding certain cover crops (e.g., hairy vetch, red clover, white/crimson clover mix) after winter wheat harvest can significantly reduce losses of nitrogen from agricultural lands by: 1) scavenging “left-over” nutrients after harvest from the crop root zone and storing the nutrients; and 2) by increasing the soil’s ability to store air and water, sequester organic carbon, and retain and recycle nutrients within the crop root zone.

The overall objective of this 4-year field study was to determine the feasibility of using legume cover crops to improve the economic and environmental performance of soybean – winter wheat – corn rotations on a fine-textured Brookston clay loam soil in southwestern Ontario. Specific objectives were to determine the efficacy of selected cover crops for: i) accumulating plant-available N in aboveground biomass; ii) providing an economically viable N credit to corn; and iii) improving soil physical quality and health. The cover crops were planted after winter wheat harvest in late July to early August, including hairy vetch, red clover, a white/crimson clover mix, and a non-cover crop control. The clovers were broadcast on the surface (at a seed rate of 12 kg/ha for red clover and 12.5 kg/ha each for white/crimson cover mix) and then the planter and chains lightly raked the soil, so the seed was just under the surface. The hairy vetch was drilled in about 180 mm apart and 10-15 mm deep at a seed rate of 25 kg/ha. Cover crop termination and corn planting included: 1) fall moldboard plow-down after first killing frost (mid to late November), then spring seed-bed preparation and corn planting; 2) spring herbicide burn-down followed by no-till corn planting; and 3) spring herbicide burn-down followed by spring strip tillage and corn planting. Crop measurements and calculations included: cover crop biomass N and carbon; soil root zone plant available N; corn stand and yield; corn leaf chlorophyll level; and apparent corn N credit. Soil quality/health measurements included: soil bulk density; soil macro-porosity; plant-available water and air capacities; soil saturated permeability; soil temperature; and soil organic carbon content.


1. On average, hairy vetch, red clover and white/crimson clovers were planted soon after winter wheat harvest and all legumes exhibited good establishment and growth, good over-winter survival, and strong spring re-growth. The amount of above-ground biomass N accumulated by winter freeze-up averaged 186, 89 and 145 kg N/ha for hairy vetch, red clover, and white/crimson clover mix, respectively. The amount of above-ground biomass N accumulated in spring re-growth before termination averaged 148, 159 and 142 kg N/ha for hairy vetch, red clover, and white/crimson clover mix, respectively.

2. Corn emergence and establishment were affected by presence-absence of cover crop, and by cover crop termination/tillage method. Relative to the no cover crop check, corn stands were 8% less for hairy vetch, 11% less for white/crimson clover mix and 15% less for red clover. Relative to cover crop termination by fall moldboard plowing, spring herbicide termination had 23% lower corn stands for no-till, and 7% lower corn stands for strip-till.

3. The annual corn grain yields varied and were affected by tillage system, by presence-absence of cover crop, and by cover crop type. Three year average corn grain yields by termination and tillage system were: fall moldboard plow (11.2 Mg/ha) > spring strip-till (10.3 Mg/ha) > spring no-till (9.2 Mg/ha). Three-year average corn grain yields by cover crop presence-absence and type were: no cover crop check (11.7 Mg/ha) > hairy vetch (10.6 Mg/ha) > red clover (9.4 Mg/ha) = white/crimson clover mix (9.2 Mg/ha).

4. Apparent legume N credits to corn varied with cover crop type and tillage system.  High and stable N credits occurred for fall moldboard plow treatments, which provided an average of 83 (62-92) kg N/ha relative to an average 48 (35-92) for no-till, and 63 (28-104) kg N/ha for strip tillage. The highest N credits occurred for fall plow hairy vetch and white/crimson clover mix (85 kg N/ha) relative to 29 to 70 kg N/ha for all other cover crop and termination combinations.

5. Soil physical quality and health improved to a generally good level under the cover crop and/or winter wheat phase of the rotation but degraded again to a generally poor level under the following corn phase. The change was about the same regardless of cover crop type and tillage system; and it appeared to be due primarily to generation of large soil pores (>0.3 mm equivalent diameter) under cover crop / wheat, followed by loss of the large pores under corn. It is speculated that this cyclic improvement-degradation pattern will gradually decrease over time, and net improvement in near-surface soil physical quality/health will eventually occur.


Although hairy vetch, red clover, and white/crimson clovers seeded after winter wheat harvest can all fix considerable amounts of N by fall freeze-up and in the following spring, the legume N credit to a following corn crop varies with legume cover crop type, how/when the cover crop is terminated, and when corn is planted. We recommend use of hairy vetch in combination with fall moldboard plow termination or spring spray-kill and strip-till, given that red clover and white/crimson clovers often provide less N than hairy vetch, and given that spring cover crop termination can delay no-till corn planting and result in poor corn emergence and corn yield.

External Funding Partners:


Project Related Publications:

Yang XM, Drury CF, Reynolds, WD Reeb, M. 2019. Legume Cover Crops Provide Nitrogen to Corn During a Three-Year Transition to Organic Cropping. Agronomy Journal. 111(6):3253-3264.

Yang XM, Drury CF, Xu W, Reeb M, Oloya, T. 2019. Rapid determinations of dissolved inorganic and organic nitrogen in soil leachate using mid-infrared spectroscopy. Canadian Journal of Soil Science. 99(4): 579-583.

Yang XM, Drury CF, Reynolds WD, Philipps LA. 2020. Nitrogen release from shoots and roots of crimson clover, hairy vetch, and red clover. Canadian Journal of Soil Science. 100(3): 179-188.

Yang XM, Reynolds WD, Drury CF, Reeb, MD. 2021. Cover crop effects on soil temperature in a clay loam soil in southwestern Ontario. Canadian Journal Soil of Science. 101: 761–770.

Yang XM, Reynolds WD, Drury CF, Reeb, MD. 2022. Impacts of summer-seeded legume cover crops and termination-tillage method on nitrogen availability to corn. In “Cover crops and green manures: providing services to agroecosystems,” editors W. D. Carciochi, J. L. Gabriel, N. Wyngaard. Frontiers in Soil Science. Invited paper and in preparation.