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Ontario Grain Farmer Magazine

Quantifying changes in soil health over time: Soil organic carbon and nitrogen storage due to long-term tillage system, crop rotation, cover crop and nitrogen fertilization

Principal Investigator: Laura Van Eerd and David Hooker

Research Institution: University of Guelph (U of G)

Timeline: September 2018 – August 2022

Objectives:

  • Using the long-term experiment at Ridgetown, which was initiated in 1995 and is applicable to humid-temperate climates, the objectives are to:
    • Assess the differences in soil health (soil organic carbon and total nitrogen) among crop rotations (Corn-Corn (C-C), Corn-Soy (C-S), Soy-Winter Wheat (S-W), Corn-Soy-Winter Wheat (C-S-W), Soy-Winter Wheat/Red Clover (S-Wrc), Corn-Soy-Winter Wheat/Red Clover (C-S-Wrc)), tillage systems (zone-tillage vs. conventional fall plow with spring secondary tillage), and nitrogen fertility treatments (starter vs. starter + 150 lb N/ac).
    • Determine the influence of time on soil organic carbon and total nitrogen accumulation by identifying sequestration rates and the change in storage from the last assessment (2006) to 2019.
    • Quantify the role of red clover cover crop and nitrogen fertilizer in crop rotation on soil organic carbon and total nitrogen storage and sequestration rates as influenced by tillage.
    • Characterize the relationship of soil health (soil organic carbon and total nitrogen) with crop yield and variability in yield among years (i.e., resiliency).

Impacts:

  • There are very few long-term trials that evaluate so many factors comparing tillage systems, crop rotation, cover crops, and nitrogen fertilizer input on soil and crop attributes. This represents a powerful opportunity to compare the impact of Ontario relevant production systems on soil health.  A significant gap in the scientific literature and knowledge is the impact of red clover cover crop and nitrogen fertilizer on soil health.
  • Most farmers know that winter wheat and red clover can improve soil health, lower fertilizer nitrogen inputs for corn, and increase crop yield stability (lower effects of drought/flooding), but research is needed to quantify how fast these improvements can be made. By comparing differences in soil health (soil organic carbon and total nitrogen) over 13 years and relating it to crop yield, we can answer this question and incentivise changes that could facilitate Ontario grain farmers to make informed management decisions.
  • If carbon trading (or taxing) policy moves forward, it is imperative that accurate Ontario soil carbon storage and sequestration rate data are available from as many different and relevant production systems. Ideally, this will help to ensure that knowledge is available so that farmers can be adequately compensated for carbon sequestration.

Scientific Summary:

Maintaining crop productivity is critical to Ontario farmers for which healthy, resilient soil plays a key role. This is particularly true in extreme weather years where drought or excessive moisture conditions are exacerbated in poor, degraded soils.  A crucial driver of soil health is organic matter and organic carbon. While winter wheat and red clover improvements on soil health and system resiliency have been well documented in Ontario, little is known on how quickly changes to soil health can be made and under which management systems. With Federal and Provincial government policies on carbon trading (or taxing), agriculture may benefit by considering carbon stored in soil. However, meaningful Ontario data are needed.  The quantity of carbon stored and the rate of carbon storage under many current different production systems (i.e., different tillage systems crop rotations, cover crops and synthetic nitrogen fertilizer inputs) may allow for farmers to be compensated for carbon sequestration.  Regardless of policy, having valid Ontario data is critical and the long-term tillage system and crop rotation trial at Ridgetown is well suited to provide this information.  

At Ridgetown, different tillage systems (no-till vs. fall plow), crop rotations (corn, soybeans, wheat with/without red clover), and nitrogen fertility treatments to corn and winter wheat were established in 1995. Previous work has demonstrated that winter wheat increased soil health after 11 years of production. However, soil organic carbon and total nitrogen stocks (two important factors of soil health) have been measured only once (2006), which was prior to when management changes were made (increase fertilizer N rates, include treatment of frost-seeded red clover into wheat, and change from no-till to zone till). Our proposed research is timed to assess the impact of these improvements to the long-term trial and to compare changes from 2006 to 2019 by quantifying soil organic carbon and total nitrogen stores and sequestration rates from 2006-2019 at Ridgetown. The proposed research will identify the combination of Ontario agricultural practices (tillage, crop rotation, cover crops, nitrogen fertility) that (i) improve soil health, (ii) have the highest capacity for sequestering soil organic carbon and total nitrogen over-time, (iii) provide resiliency to the system by relating soil health with crop yield and variability between years.

External Funding Partners:

Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) through the Ontario Agri-Food Innovation Alliance

Mitacs Elevate Program

This project was funded in part by the Ontario Agri-Food Innovation Alliance.