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Ontario Grain Farmer Magazine

Long-term vs. first-time cover crop use: Can cover crops enhance nitrogen availability to corn and organic nitrogen and carbon storage at the same time?

Principal Investigator: Laura Van Eerd

Research Institution: University of Guelph

Timeline: July 2022 – June 2024  

Objectives:

The proposed research will establish long-term vs. first-time cover cropping to:

  • Quantify nitrogen (N) availability to grain corn by using the 15N tracer technique.
  • Enhance understanding of the mechanism of N availability under cover cropping by delineating the profile distribution of soil organic N and carbon (C) within soil organic matter (SOM) fractions (i.e., POM-particulate organic matter and MAOM-mineral-associated organic matter).
  • Evaluate economics of cover cropping (i.e., partial profit margins: cost of cover crop seeds and planting, revenue from crop yield, soil organic N and C storage).

Impacts:

  • The estimation of N availability to grain corn by comparing long-term vs. first-time vs. no cover cropping will help farmers to adjust (i.e., reduce) the application rate of mineral N without crop yield loss. The improvement of N use efficiency with the time since the introduction of cover crops (CCs) also can reduce N loss from croplands to groundwater (e.g., nitrate leaching) and atmosphere (e.g., nitrous oxide emissions).
  • The analysis of soil organic N and C across SOM fractions (i.e., POM and AMOM) within soil profile will help scientists understand N availability and soil organic C storage response to cover cropping with time. Especially, it provides an opportunity to predict the capacity of long-term cover crops to mitigate climate change by soil organic C sequestration.
  • The comparison of N availability, soil organic C store, and economical returns among long-term vs. first-time vs. no cover cropping will improve farmers’, consumers’, and the government confidence in the adoption of cover crops.

Scientific Summary:

Cover crops have been widely touted to increase soil organic nitrogen (N) and carbon (C) storage. However, these benefits are expected after long-term use while additional costs of planting cover crops are immediate. This is the main barrier to cover crop adoption. To reduce this risk, we will comprehensively investigate the economic and environmental performance (e.g., N availability and soil organic C storage) of long-term and first-time and no cover cropping in the same fields. In 2007, Prof. Van Eerd established the cover cropping experiment in a vegetable-grain rotation at Ridgetown and repeated it in 2008. In this experiment, cover crop plots had about 17% greater soil health score in 2015/2016, and >30% greater corn yield in 2020/2021, compared to no cover crop plots. We hypothesize that N availability to the following crop has been enhanced, due to greater SOM (i.e., greater C and N storage) under long-term cover cropping. Grain farmers probably are more interested in “How much N fertilizer I can save from the long-term cover cropping?”

The proposed research will test our hypothesis and answer the farmers’ question above. We will quantify N use efficiency by grain corn and identify possible mechanism of N availability enhancement in long-term vs. first-time cover cropping. We will sacrifice part of the no cover crop plots where selected cover crops will be planted for the first time. However, it is a challenge to accurately calculate the amount of plant available N from cover crops to the following crop. Hence, the 15N tracer will be employed to follow the 15N-enriched fertilizer applied to cover crops after emergence and transferred to the grain corn. Meanwhile, we will explore the distribution of N and C within SOM fractions to determine soil organic N and C stores and their relationship with N availability. Additionally, the economic impacts of grain corn with and without cover crops will be analyzed to assess the economic returns to cover crops with time (i.e., 15-years vs. 1-year).

External Funding Partners:

Matching funding was provided by the Fresh Vegetable Growers of Ontario and the Ontario Agri-Food Innovation Alliance, a collaboration between the government of Ontario and the University of Guelph.