Reducing Soil N20 Emissions in Canadian Agricultural Soils

Image result for n2o molecule
N2O Molecule. Image from: https://fineartamerica.com/featured/nitrous-oxide-laughing-gas-molecule-molekuulscience-photo-library.html

Canada has committed to reducing its greenhouse gas (GHG) emissions to 30% below 2005 level by 2030. In 2017, Canada’s GHG emissions, in CO2 equivalents (CO2e) were 716 Mt – just 2% lower than 2005 emissions. Agriculture represented 8.4% (60 Mt CO2e) of Canada GHG emissions in 2017, 42% (25 Mt CO2e) of which was due to soil N2O emissions (3.4% of Canada’s total emissions). As a GHG, N2O has 300 times the warming, or radiative forcing, potential of CO2.

Even though agricultural soils only represent 3.4% of Canada’s total GHG emissions, soil GHG emissions have increased by 32% since 2005 from 19 Mt CO2e to 25 Mt CO2e. The Government of Canada has identified an increase in nitrogen fertilizer use in the prairies as the main culprit of this emissions increase. Nitrogen is a crucial plant nutrient and farmers rely heavily on synthetic forms of nitrogen to deliver this nutrient to plants.

Although we are looking here at soil N2O emissions through a Canada-based GHG emissions and climate change lens, it is actually a much more complex issue than that:

  1. While synthetic nitrogen clearly results in enhanced plant growth, it does not contribute to soil health and, in fact, can be quite detrimental to soil health over time.
  2. Studies suggest increases in fertilizer use could be due to decreased soil health from excessive nitrogen fertilizer use, requiring farmers to apply more fertilizer to simply maintain yields – but at an increased cost.
  3. Excess nitrogen applications can result in excess emissions (e.g., fertilizer off-gases before being absorbed by plants) and leaching into waterways which can cause eutrophication – anoxic conditions in waterways which suffocate marine organisms.
  4. The manufacture of synthetic nitrogen fertilizer alone is responsible for approximately 1.1% of global GHG emissions (~410 Mt in 2017) and reducing its use will reduce its production.

While addressing and reducing soil N2O emissions in Canada may make a relatively small impact on overall GHG emissions in Canada, it will make a big impact on agricultural emissions and, with the right strategies, improve soil health for Canadian farmers.

We thus proposed two approaches, based on IPCC recommendations, to reducing soil N2O emissions in Canada. which will have multiple positive impacts and address the points above:

  1. Improved Nutrient Management
  2. Improved Soil Conservation Practices
Image result for variable rate nutrient application
Graphic showing how VRNA works. Image from: https://www.pinterest.ca/pin/316448311289440455

A key approach to improving nutrient management and reducing nitrogen use, without affecting crop yields, is through variable rate nutrient applications (VRNA). In short, by using already existing technology, which many farmers have already integrated into their farming systems, farmers can apply nitrogen fertilizer more precisely using soil nutrient data (from comprehensive farm soil tests). This allows farmers to apply more or less fertilizer at various points in their fields based on the needs of that specific area. Studies have shown this can reduce nitrogen fertilizer costs for farmers while maintaining or improving crop yields – all while reducing soil N2O emissions – a win-win-win for farmers! Our basic calculations (see below) suggest this could reduce soil N2O emissions by 1.5Mt CO2e/year (6% reduction).

Soil conservation practices include activities such as crop rotation – changing which crops grow in fields each year; and, cover cropping – the practice of growing crops which farmers then turn back into the soil to increase soil organic matter and microbial activity. Several cover crops, such as alfalfa and fava beans, also form symbiotic relationships with soil bacteria and can actually “pull” nitrogen out of the atmosphere (which is 78% nitrogen) and make it available to plants for uptake. This nitrogen “fixing” property of these cover crops can actually add more nitrogen to the soil than is required by most primary prairie crops on a seasonal basis. These practices could reduce soil N2O emissions by a further 2.2 Mt CO2e/year (8.8%).

With these two approaches combined, farmers could reduce soil N2O emissions by close to 15%, and over time, reduce emissions even more due to increased soil health which, with increased organic matter content and microbial activity due to cover cropping, will be further reducing atmospheric CO2 and storing it in the soil.

Such approaches to reducing N2O emissions may not come cheap (especially in the beginning), but the federal government already has numerous grant and loan programs in place to support such initiatives and through its global obligations to reduce GHG emissions has a strong incentive to support such approaches to reduce GHG emissions. Further, because of the numerous on-farm (yield and cost savings) and bigger-picture climate (reduced emissions) and ecological health (reduced runoff and leaching) benefits, and with financial and training support through government funding, the likelihood of adoption of these technologies and practices by farmers is quite high.

While the soil GHG emissions reductions gained in this approach may seem low as a percentage of Canada’s total emissions, by addressing soil N2O concerns, the numerous complementary benefits that arise speak strongly in support of this approach to not only lessen Canada’s impact on the climate but also improve the health of our agricultural system.

 

Chris

 

While I have taken advantage of the blog format to avoid adding numerous tedious in-text citations I have included an annotated reference (with calculations) below along with the names of my group partners who contributed so much to this research.

 

 

Annotated Bibliography 

Reducing N2O Emissions from Agricultural Soils in Canada

Natalie Rivlin, Ryah Rondolo, Georgia Stanley, Chris Thoreau

 

Balafoutis, A., Beck, B., Fountas, S., Vangeyte, J., Van Der Wal, T., Soto, I., Gómez-Barbero, 

M., Barnes, A., Eory, V. (2017). Precision agriculture technologies positively contributing 

to GHG emissions mitigation, farm productivity and economics. Sustainability, 9(8), 

1–28.

  • Detailed paper on the different precision agriculture technologies for more efficient use of nitrogen in an effort to reduce N2O emissions from agricultural soils, while also accounting for farmer costs. It provides scientific evidence and background for the potential effectiveness of variable rate nutrient application as a mitigation strategy.       

Dorff, E., & Beaulieu, M. S. (2014). Feeding the soil puts food on your plate. Statistics Canada. 

Retrieved from: 

https://www150.statcan.gc.ca/n1/en/pub/96-325-x/2014001/article/13006-eng.pdf?st=FfR

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  • Statistics Canada report showing increased use of nitrogen fertilizer in Canada, as well as stating national lime and nitrogen costs to farmers in 2010 as $3.6 billion, which we used to calculate potential cost saving for farmers using VRNA.

Eilers, W., MacKay, R., Graham, L., & Lefebvre, A. (2010). Environmental sustainability of 

Canadian agriculture: Agri-environmental indicator report series–report #3. Agriculture 

and Agri-Food Canada, Ottawa, ON.

  • This article examines the impact of synthetic nitrogen fertilizers on ecosystem health. It informed the “Impacts” section in our infographic. 

Environment and Climate Change Canada. (2019). National inventory report 1990–2017: 

Greenhouse gas sources and sinks in Canada, Canada’s submission to the United Nations 

framework convention on climate change. Retrieved from: 

https://www.canada.ca/en/environment-climate-change/services/climate-change/greenho

use-gas-emissions/inventory.html

  • This was our primary statistical source for agriculture related GHG emissions in Canada, which attributed the rise in agricultural soil emissions to increased nitrogen fertilizer use in the prairies.

FAO. (2017). World fertilizer trends and outlook to 2018. Food and Agriculture Organization of 

United Nations. Retrieved from: http://www.fao.org/3/a-i6895e.pdf

  • Source for world nitrogen fertilizer use statistics. 

Gunningham, N. (2007). Incentives to improve farm management: EMS, supply-chains and civil 

society. Journal of Environmental Management, 82(3), 302-310. 

  • This text informed and shaped our recommended policy strategies. It explores challenges Australian farmers face in adopting environmentally sound practices, and emphasizes the need to use multiple strategies simultaneously to support positive outcomes in environmental management systems in agriculture. 

Le Quéré, C., Andrew, R. M., Friedlingstein, P., Sitch, S., Hauck, J., Pongratz, J., Pickers, P.A., 

Korsbakken, J.I., Peters, G.P., Canadell, J.G. & Arneth, A. (2018). Global carbon budget 

  1. Earth System Science Data (Online), 10(4).
  • Source for 2018 total global GHG emissions. 

Mulvaney, R. L., Khan, S. A., & Ellsworth, T. R. (2009). Synthetic nitrogen fertilizers deplete 

soil nitrogen: A global dilemma for sustainable cereal production. Journal of 

environmental quality, 38(6), 2295-2314.

  • This article suggests that synthetic nitrogen fertilizers deplete organic soil nitrogen and lead to crop yield stagnation or decline over time. 

Reay, D. S., Davidson, E. A., Smith, K. A., Smith, P., Melillo, J. M., Dentener, F., & Crutzen, P. 

  1. (2012). Global agriculture and nitrous oxide emissions. Nature climate change, 2(6), 

410.

  • This article examines the impact of synthetic nitrogen fertilizers on global climate change. It helped inform the “Impacts” section in our infographic. 

Signor, Diana, & Cerri, Carlos Eduardo Pellegrino. (2013). Nitrous oxide emissions in 

agricultural soils: A review. Pesquisa Agropecuária Tropical, 43(3), 322-338. 

  • This article provides a summary of nitrous oxide mitigation practices for agricultural soils. It helped inform the selection of our strategies (e.g., improving fertilizer use efficiency).

Skiba, U. M., & Rees, R. M. (2014). Nitrous oxide, climate change and agriculture. CAB 

Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural 

Resources, 9(June 2015).

  • This IPCC report documents the estimated mitigation potential of multiple strategies, which we used to calculate potential emissions savings.

Smith, P., D. Martino, Z. Cai, D. Gwary, H. Janzen, P. Kumar, B. McCarl, S. Ogle, F. O’Mara, C. 

Rice, B. Scholes, O. Sirotenko. (2007). Agriculture. In Climate Change 2007: Mitigation. 

Contribution of Working Group III to the Fourth Assessment Report of the 

Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R. Bosch, R. 

Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge, United Kingdom and 

New York, NY, USA.

  • This IPCC report documents the estimated mitigation potential of multiple strategies, which we used to calculate potential emissions savings.

Statistics Canada. (2019). Table 32-10-0039-01 Fertilizer shipments to Canadian agriculture 

markets, by nutrient content and fertilizer year, cumulative data (x 1,000). Retrieved 

from: https://doi.org/10.25318/3210003901-eng

  • Statistical data for nitrogen fertilizer usage in Canada by province. 

Stuart, D., Schewe, R. L., & McDermott, M. (2014). Reducing nitrogen fertilizer application as a 

climate change mitigation strategy: Understanding farmer decision-making and potential 

barriers to change in the US. Land use Policy, 36, 210-218. 

  • This article explores factors impacting American farmers’ decision-making surrounding the adoption of inorganic nitrogen fertilizer reduction practices. It informed our recommended policies, and provided context surrounding barriers to adoption of fertilizer reduction practices, including reasons for fertilizer overuse, and the role of additional policies to support the effectiveness of financial incentives. 

Ward, M. H. (2009). Too much of a good thing? Nitrate from nitrogen fertilizers and cancer. 

Reviews on environmental health, 24(4), 357-363.

  • This article examines the impact of synthetic nitrogen fertilizers on human health. It helped inform the “Impacts” section in our infographic. 

Wood, S., & Cowie, A. (2004). A review of greenhouse gas emission factors for fertiliser 

production. IEA Bioenergy Task 38. Retrieved from: 

http://large.stanford.edu/courses/2014/ph240/yuan2/docs/wood.pdf

  • This report states the production of inorganic fertilizers contributes 1.2% of global emissions and helped with our calculations on N-manufacturing emissions

 

Calculations

 

Potential GHG Reductions from Proposed Strategies

From Skiba and Rees (2014), Table 8.4, p. 512 – Data for Warm-Dry Climate 

Part I: GHG Mitigation Potential for Agronomy and Nutrient Management

    • Agronomy
      • Includes: Cover cropping; crop rotation strategies; legumes
      • Potential Mitigation (tCO2e/ha/year):
        • Low: 0 
        • High: .20
        • Mean: .10 (used for Agronomy mitigation calculation below)

 

 

    • Nutrient Management
      • Includes: VRNA; time release fertilizers
      • Potential Mitigation (tCO2e/ha/year):
        • Low: .01 
        • High: .32
        • Mean: .07 (used for Nutrient Management mitigation calculation below)

 

 

Part II: Calculations with Select Major Prairie Crops

 

  • Crops: Canola, Wheat, Barley, Oats
  • Area (Ha) in AB, SK, and MB: 22,199,000 (~⅛ Canada’s farmland)

 

    • Mean Agronomy mitigation potential = 22,199,000 Ha * .10 tCO2e/ha/year = 2.2 Mt/year mitigation
    • Mean Nutrient Management mitigation potential = 22,199,000 HA * .07 tCO2e/ha/year = 1.5 Mt/year mitigation

 

  • Total = 3.7 MtCO2e/year mitigation

 

 

Cost Savings Potential to Prairie Farmers from Variable Rate Nutrient Application 

Various studies cited by Balfoutis et al., (2017) show the following range of farm cost savings using VRNA:

    • 4 – 7% N $ savings with VRNA
    • 6 – 46% N $ savings with VRNA 
    • 21% N $ savings with VRNA
    • All are usually accompanied by increased yields

We used 10% as an estimated cost-saving value for calculations
Lime and N fertilizer in 2010: $3.6 Billion in expenses to farmers (Dorff & Beaulieu, 2014)

  • Using 10% savings as an estimate from above = $360,000,000 in total savings (Lime and N)
  • Conservatively reduced estimate to $250,000,000 in annual N savings as lime use is almost non-existent in prairies and they also account for 85% of fertilizer use

 

Canada’s Share of Global Nitrogen Manufacturing Emissions

1.2% of global emissions come from fertilizer production, 93% of which is nitrogen, equating to 1.1 % of global emissions (CO2e) from N production (Wood & Cowie, 2004)

  • For 2018, N-production would account for 1.1% * 37.1 Gt of CO2e GHG (Le Quéré et al., 2018) = .411 Gt of CO2e or 411 Mt CO2e
  • Estimated 2018 world N use: 115,376 Mt (FAO, 2017)
  • Canada N use 2017/2018 = 2600 Mt (Statistics Canada, 2019)
    • 2600 Mt (Canada)/115,376 Mt (Global) = 2.2% of global N fertilizer use
    • 2.2% * 411 Mt CO2e globally from fertilizer production = ~9Mt CO2e

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