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Interseeding cover crops options for grain corn and their effects on soil health in Southern Ontario

Principal Investigator: Mehdi Sharifi and David Hooker

Research Institution: Trent University and University of Guelph

Timeline: April 2015 – May 2018


  • Assess the most common cover crop species and their mixture for their establishment rate, biomass production, and competitiveness with grain corn in three major Southern Ontario corn growing regions.
  • Evaluate the effect of interseeding cover crops on a range of soil health parameters with short-term turnover including soil pH, total soil organic carbon (C) and nitrogen (N), particulate organic matter C and N, readily mineralizable soil N, soil mineral N (NO3+, NH4), microbial biomass C and N, and soil enzyme activities (beta-glucosidase and dehydrogenase).


  • The adoption of interseeded cover crops has the potential to increase soil organic matter, which may lead to several benefits such as enhanced soil water holding capacity, water infiltration rate, soil health, and nutrient cycling.
  • The adoption of interseeded cover crops has the potential to improve long-term soil productivity, profitability and environmental sustainability for Ontario grain production.

Scientific Summary:

Long-term crop rotation research in Ontario (University of Guelph) has shown that a corn-soybean rotation has lower productivity compared to more diverse rotations that include wheat, especially during growing seasons with a shortage or excessive rainfall. Lower productivity is associated with poor soil structure and lower soil organic carbon (C) compared to more diverse rotations. The importance of building resilient soils and best cropping practices is evident, but convincing grain farmers to grow perennial crops or incorporate cover crops in crops other than wheat has been a challenge. One promising option for extending corn-based rotations benefits to ensure long-term profitability in cool temperate climate is to introduce interseeding cover crops in corn. Establishing a cover crop into corn has the potential to build resilience in short rotations with improvements in soil health. It is therefore important to investigate interseeding cover crop options, benefits, risks and uncertainties.

This project investigated impacts of interseeding cover crops into grain and silage corn on yield and soil health. At three locations in Ontario (Ridgetown Campus, Elora Research Station, and Trent University Experimental Farm in Peterborough), corn was interseeded (using interseeder equipment by InterSeeder Technologies Inc. from Penn State) with four cover crop treatments at the V5 developmental stage: 1) red clover, 2) annual ryegrass, 3) 1:3.3 mixture of red clover and annual ryegrass, and 4) broadcast mix of red clover and annual ryegrass. Plots without interseeded cover crops were included as controls for comparison, bringing the total number of plots (including 4 replications of each treatment) at each site to 20. The experiment was repeated for three seasons from 2015 to 2017; however, not all site-years were available. The final outcome of the project was a ranking of the interseeding cover crop treatments in terms of establishment, biomass production, competitiveness with grain corn, and effects on sensitive indicators of soil health and residual soil nitrate at harvest. The soil health and soil nitrate reduction benefits were linked with long-term environmental sustainability.


  1. Cover crops can be interseeded into grain corn at the V5 stage without detriment to grain and silage corn yield or N uptake.
  2. Soybean yield was not affected by the previous interseeded cover crops treatment in corn.
  3. Cover crop biomass in an interseeded system will vary widely depending on climatic conditions and the competitiveness of the corn crop cultivar. Annual ryegrass was more resistant to drought and performed better in dry seasons compared to red clover. However, annual ryegrass control in the spring of the following year is difficult and should be done before stem elongation stage, which is early in the spring. Moreover, annual ryegrass is high risk for developing herbicide resistance.
  4. Drilling the interseeding cover crops was more effective than broadcasting for early season establishment and growth, especially when precipitation was limited around seeding time.
  5. At the end of the growing season (November), greater cover crop biomass was observed following silage corn when compared to grain corn.
  6. Weed biomass is suppressed by successful cover crop stand establishment. In grain corn plots, interseeded cover crops reduced weeds by up to 50%.
  7. The cover crop establishment and growth at the time of grain harvest might have been inadequate to reduce residual soil N levels in Southern Ontario; however, the average of residual soil N values in annual ryegrass treatment across sampling date and sites was 48% and 27% lower than control treatment, and average of red clover and mixture treatments, respectively.
  8. Interseeded cover crops accumulated 15-860 kg C ha-1 and 1.3 to 77 kg N ha-1 to soil each season. The high end of the range for C and N was associated with successful establishment of cover crops and favorable growth conditions.
  9. Community-level physiological profiling showed significantly greater microbial diversity with annual ryegrass compared with control.
  10. Cover crop residues did not change the corn stover decomposition rate (C and N mineralization); although, there was a trend towards greater rate of corn stover (C and N) decomposition with addition of cover crop residues.
  11. Overall, the combination of annual ryegrass or red clover with corn did not enhance net C mineralization relative to corn alone.
  12. Compared to soil without residues, corn residues did not significantly change the size of the labile C pool, but when corn was added in combination with annual ryegrass and red clover residues, labile C increased by 25% and 27%, respectively.
  13. N immobilization lasted about 60 days, and was highest in the soil amended with corn residues due to their higher C:N ratios.
  14. The addition of annual ryegrass and red clover residues did not reduce N immobilization in soil amended with corn residues. This may be due to the corn residues accounting for ~90% of added residue C.
  15. Seasonal effects of interseeded cover crops on soil health indicators were not detectable. The lack of cover crops effect on selected soil health indicators can be attributed to short-term nature of the experiment, larger amounts of corn stover residues compared with cover crops residues or high environmental variability which might have masked the cover crop effects.
  16. Further investigation of a wider range of interseeding cover crops in grain corn over multiple rotation cycles may allow detection of long-term effects on yield, N uptake, N dynamics in soil, and soil health. Effect of this practice on crop residue decomposition and soil C and N dynamics in the next crop (soybean) is also important and requires further examination.

External Funding Partners:

This project was funded in part through Growing Forward 2 (GF2), a federal-provincial-territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario.

Project Publications:

Clark, J.C., Deen B., Hooker, D., Sharifi, M. 2018. Opportunities for the Inclusion of Cover Crops in the Corn-Soybean Rotation in Ontario. MSc thesis. Department of Plant Agriculture, University of Guelph, Guelph, ON.

Katanda, Y., Hutchinson, T., Thompson, K., Van Eerd, L., Hooker, D., Sharifi, M. 2020. Soil Health, Nitrogen Supply, and Residue Decomposition in Interseeded Cover Crop-Grain Corn Systems in Ontario. PhD thesis. Trent University, School of Environment, Peterborough, ON.

Katanda, Y., Hutchinson, T., Sharifi, M., Van Eerd, L., Hooker, D. 2018. Can cover crop residues reduce nitrogen immobilization during corn stover decomposition? CGU-CSSS-CIG-ESSSA-CSAFM Joint Annual Meeting, June 10-14, Niagara Falls.

Katanda, Y., Sharifi, M., Hooker, Deen, B., and Messiga A.J. Interseeded cover crops, soil health and nitrogen supply for grain corn in Ontario.2018. Soil and Crop Conference, March 6-7, Saskatoon, SK, Canada (Poster)

Katanda, Y., Sharifi, M., Hooker, Clark, and Messiga A.J. Interseeded cover crops, soil health and nitrogen supply for grain corn in Ontario. 2018. Soil and Crop Conference, March 6-7, Saskatoon, SK, Canada (Oral)

Katanda, Y., Sharifi, M., Van Eerd, L. L. Hooker, D.C. 2017. Interseeded cover crops effects on dynamic indicators of soil health. ASA-CSSA-SSSA 2017 International Annual Meeting. Oct. 22-25, Tampa FL., USA. (Oral presentation; #29-14)

Katanda, Y., Sharifi, M., Hooker, D.C. Van Eerd, L. L,. Clark, J., Deen, B., Messiga A.J. 2017 Interseeded Cover Crops and Soil Nitrogen Supply for Grain Corn in Ontario. 2017 Canadian Society of Soil Science Annual Meeting, June 10-14, Peterborough, Ontario. (Oral)

Clark, J., B. Deen, D. Hooker, M. Sharifi., L. Van Eerd, Y. Katanda. 2016. The potential of interseeding cover crops into corn to address issues in the corn-soybean rotation. ASA-CSSA-SSSA 2016 International Annual Meeting. Nov. 6-9, Phoenix AZ., USA. (Poster presentation; #328-418)

Interview: Karen Dallimore. 2015. Can cover crops benefit a corn-soy rotation? Interview with Today’s Farmer Magazine. August 11.