Trying to Make Sense of Canada’s Greenhouse Gas Reduction Plans for Agriculture

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This overview has been written for those in Canadian agriculture trying to understand what recent announcements and new funding commitments from Ottawa on net greenhouse gas (GHG) emissions mean for Canadian farmers. The subject is quite confusing; indeed, it’s tempting for agriculturalists to just ‘tune out.’ However, because of the combination of anticipated obligations and the impending availability of financial incentives, I believe progressive farmers need to be well informed. In the following, I’ll try to make the complex as simple as I can while not missing critical details:

  • Agriculture GHG emission accounting has been managed in a confusing manner ever since member countries like Canada began submitting annual ‘Net Inventory Reports’ (NIR) on GHG emissions to the United Nations Framework Convention on Climate Change (UNFCCC) sometime during the 1990s. These NIR calculations are based on reporting protocols specified by the Intergovernmental Panel on Climate Change. What’s classed as ‘Agriculture’ actually includes only a portion of agriculturally related net emissions – specifically, emissions associated with livestock farming, manure, nitrogen fertilizer application, carbon dioxide (CO2) released during urea and lime applications to soil, rice paddy nitrous oxide (N2O) emissions, and a few others. But fossil fuels used in agriculture, energy used for fertilizer manufacturing, CO2 credits for biofuels produced from farm crops and processing byproducts, and net CO2 emissions from the creation and breakdown of farm soil organic matter are not included. Nor is any credit given to agriculture for the carbon contained in farm products sold off the farm – including crop exports to other countries. The oft-quoted ~8% of total national emissions attributed to agriculture – or about 59 M t/year of CO2 equivalent out of the 730 Mt Canadian total according to the most recent data (year 2019, data accessible here) – is an artifact of the calculation procedure. The number would be larger or smaller if various other items were included. I have discussed the significance of this elsewhere (here).
  • In a partial attempt to address this, Environment and Climate Change Canada (ECCC) in preparing NIRs and related reports combines emissions classed by IPCC as agriculture with fossil fuel usage on farms to calculate the ‘Sectoral’ contribution from agriculture. The most recent number is 73 Mt/yr CO2e. However, this summation does not include other agricultural-related net emissions, especially the critical CO2 exchanges between soil and atmosphere that are highly dependent on both type of farming and differences in farm management. CO2 exchanges with farm soils are combined with similar ones from forestry, peat and wetland management and others in a category called Land Use, Land Use Management and Forestry (LULUCF). In the most recent Canadian NIR, agricultural land was a sink (negative net emission) for CO2, equivalent to 4 Mt/yr CO2e, even though the total LULUCF for Canada was positive because of larger emissions contributions from the other components.
  • The Government of Canada added significantly to the confusion with its publication in December 2020 of a major climate change document, A Healthy Economy and a Healthy Environment. In it, ECCC created a category called Natural Climate Solutions (NCS) that is similar to LULUCF but also involves additional agricultural items, including emissions from fertilizer application to farm soils. The choice of the term, ‘Natural Climate Solutions,’ and the high profile given to it were likely political; the term has received strong support in recent years from many NGOs and others. There was a major national ‘summit’ on this in Ottawa in early 2020, funded partly by ECCC. However, the decision to diverge from the IPCC/UNFCCC approach and place several farm-related items in NCS and not ‘Agriculture’ was most confusing to those of us in agriculture.  See the following Table extracted from an appendix to the report (available here), where ‘Natural Climate Solutions’ is relabelled as ‘LULUCF, NBS and agriculture measures,’ with NBS standing for ‘nature-based solutions.’

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  • This brings us to the 271-page 2030 Emissions Reduction Plan issued the Government of Canada on March 29, 2022 (available here) which includes separate sections for both Agriculture and what was earlier called Natural Climate Solutions, now called Nature-Based Solutions (also sometimes referred to in the report as ‘Nature-Based Climate Solutions’). The Agriculture section features the ‘Agricultural Sector’ emission of 73 Mt/yr CO2e (mainly livestock, manure and N fertilizer, plus farm fuel, as stated above), but then says, “Agricultural soils are also a significant carbon sink. In 2019, agricultural soils stored slightly more than 4 Mt, offsetting approximately 6% of total annual agricultural emissions.” The implication is that the 4 Mt amount is included in the Agricultural Sector sum of 73 Mt – which it is definitely not. Indeed, if the agricultural community were to increase the soil sink carbon storage to twice the 2019 amount – say 8 Mt/yr – the Agricultural Sector sum of 73 Mt/yr as calculated by ECCC would not change.
  • Perhaps less critical but still misleading is this statement a few paragraphs later: “Canadian agricultural soils have transformed over the last 20 years from a carbon source to a carbon sink.” That is true if any year before 2000 is used as the base. However, as this graph extracted from the March 2022 document shows, the annual carbon sink storage of Canadian farm soils has mostly decreased in recent years – largely as a result of a declining national beef herd size, and a consequent shift of perennial forages into annual crops. Those who advocate for reduced beef production/consumption in Canada are not allies of efforts to increase the size of the agricultural soil carbon reserve.

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This brings us to the Government of Canada (GoC) commitment for GHG reductions: 

  • In its December 2020 report, the GoC called for no reduction in Agriculture emissions by 2030 – and actually a small increase of 2 Mt CO2e/year to 74 Mt CO2e/year – compared to base year 2005. (See Table above). The projection was also for a 27 Mt/yr CO2e reduction in net emissions in ‘LULUCF, NBS and agriculture measures’ with about 17 Mt of this to come from changes in LULUCF and 10 Mt/yr of the reduction to come from the combination of reduced nitrogen fertilizer use in agriculture and ‘nature-based solutions.’ Based on data in the Canadian NIR (see above; also see here), it appears that reduced fertilizer usage represents about 4 Mt of the 10 Mt/yr.
  • These projected targets for 2030 from the 2020 report were altered only slightly in the document released in March 2022 (here). The 2030 goal for Agriculture was reduced to 73 Mt/yr CO2e for Agriculture from 74 Mt. The 2030 goal for Natural Climate Solutions (aka, LULUCF, NBS and agriculture measures) was reduced to -30 Mt/yr CO2e from -27 Mt. On first glance, Agriculture appears to be targeted for almost no reductions. However, the real agricultural reductions are in the LULUCF, NBS and agriculture measures section, including N fertilizer use reduction and carbon sequestration in farm soils.
  • If you check the fine print in the March 2022 document (See page 214 to 219 in an appendix section called, Modelling and Analysis of Canada’s Emissions Reduction Plan for 2030), you’ll find that the 2022 numbers actually differ substantially from those in the December 2020 report and/or the most recent NIR. For example, the 2030 reduction goal for the LULUCF portion changes from -17 Mt/year to -11 Mt, and the NBS and agricultural measures portion almost doubles, to -19 Mt/yr from -10 Mt.
  • To add to the confusion, the March 2022 document gives almost no guidance as to what is classified as a reduction in LULUCF, or NBS or agricultural measures (the exception being that the 4 Mt reduction for N fertilizer usage is clearly an ‘agricultural measure’). To read the text, it would imply that C sequestration associated with no-tillage and changes in cropping and crop cover would be a ‘nature-based solution’ and/or an ‘agricultural measure.’ However, the Canadian NIR documents make it clear that these are captured in LULUCF. So what’s to be changed and how will the GHG accounting occur? Who knows?
  • Bottom line: The 2030 Emissions Reduction Plan is for a reduction of 30 Mt/yr of CO2e by 2030 for LULUCF, nature-based solutions and agricultural measures, but the document provides almost no information as to what this means beyond vague generalities.
  • There is obviously more to come. For example, note this excerpt from a paragraph on Page 66: “Going Further – the Government of Canada commits to explore additional opportunities, including: …..Advance a Green Agricultural Plan for Canada, in consultation with the agriculture and agri-food sector, Indigenous Peoples, and other stakeholders, to establish a long-term vision and approach to agrienvironmental issues in order to advance the sustainability, competitiveness, and vitality of the sector.”
  • Those who interpret the March 2022 document as meaning little change for agriculture are very mistaken. 

Finally, let’s take a look at programs and funding: 

  • In December, 2020, the GoC initiated an ‘umbrella’ Natural Climate Solutions Fund, committing $3.16 billion to Natural Resources Canada over 10 years to plant 2 billion trees, $631 million to ECCC to “restore degraded ecosystems, protect wildlife, and improve land and resource management practices,” and $98.4 million in new funds to Agriculture and AgriFood Canada to be added to ~$85 million in reallocated money to created a new, $185 million Natural Climate Solutions for Agriculture Fund (NCSAF) (see here and here).
  • In March 2021, AAFC announced more details for NCSAF (including the Living Labs research and outreach program) and added $165.7 million for the Agricultural Clean Technology Program (ACTP) “that supports research, development and adoption of clean technologies.”
  • In the April 2021 Budget, the GoC added $200 million to the now renamed Agricultural Climate Solutions (ACS) Fund – bringing the total to $385 million – and allocated $50 million of ACTP funds for purchase of more efficient farm grain dryers (reference).
  • In December 2021, AAFC clarified that $185 million of ACS will be used to fund Living Labs research over 10 years and $200 million would go to a new 3-year, Agricultural Climate Solutions – On-Farm Climate Action Fund (ACS-OFCAF) “that will support farmers in adopting beneficial management practices (BMPs) that store carbon and reduce greenhouse gases in three areas: nitrogen management, cover cropping and rotational grazing practices” (reference).
  • In February 2022, AAFC announced that $182.7 million of ACS-OFCAF would go to 12 organizations to reduce GHG emissions by up to 2 million tonnes. (This is about double the cost per tonne compared to a recommendation from Farmers for Climate Solutions on which the ACS-OFCAF program was based. No explanation for the doubling was provided.) Usage of the remaining $17.3 million, out of the $200 million, remains unknown.
  • In March 2022, as part of its 2030 Emissions Reduction Plan, the GoC announced another $270 million (to a total of $470 million) to ACS-OFCAF to “allow the program to top-up funding for some current successful applicants, broaden support to additional key climate mitigation practices, extend the program past its current end date of 2023/24, and support adoption of practices that contribute to the fertilizer emissions target and Global Methane Pledge.” The Canadian fertilizer emission reduction strategy is described here. The Global Methane Pledge is an international pledge made in late 2021 with few, if any, details released as of yet for Canadian agriculture.
  • An additional $150 million was announced in March 2022 “for a resilient agricultural landscapes program to support carbon sequestration, adaptation and address other environmental co-benefits.”
  • In its April 2022 Budget, AAFC added “$329.4 million over six years to triple the size of the Agricultural Clean Technology Program” and another “$100 million over six years to the federal granting councils to support post-secondary research in developing technologies and crop varieties that will allow for net-zero emission agriculture.”
  • There is a listing of programs and expenditures for both Agriculture and Nature-Based Solutions, in a final chapter of 2030 Emission Reduction Plan, but it provides no details on delivery plans and expected achievables for the specific programs/expenditures.

Some summary conclusions/opinions: 

  • A substantial amount of money has been committed by Ottawa since late 2020 for reductions in net GHG emissions in agriculture and related areas.
  • There appears to be large expenditures for cover crop establishment for which the underlying scientific support is weak (in my opinion) and for which it will be almost impossible to measure changes in soil carbon storage for many years.
  • I am more comfortable with the approach recently announced by AAFC for nitrous oxide emission reductions associated with fertilizer usage.
  • The steps announced to date for reductions in methane emissions in agriculture (largely related to ruminant animals) are vague and apparently minimal.
  • Curiously, and disappointingly at least for agriculture, none of the federal announcements or commitments refers to opportunities to increase albedo reflectance (the portion of incoming short-wave radiation reflected back into space). Practices such as no tillage and the use of land for annual cropping versus forest cover can mean important increases in albedo percentages. For example, in this recent paper, AAFC researchers concluded that albedo changes caused by no tillage in Prairie Canada have been more important than the associated soil carbon sequestration in reducing atmospheric warming potential.
  • The split of agriculture into two distinct compartments, Agriculture and Natural Climate Solutions (aka, Nature-Based Solutions) is likely to lead to future strategic difficulties for Canadian agriculture. Firstly, the 2030 Emissions Reduction Plan calls for essentially no reductions in net emissions for what it terms as Agriculture, but 30 Mt/yr of CO2e for it calls NCS/NBS. A recent reaction by one prominent Canadian agricultural groups (check here) is an example of what’s ahead. All major reductions proposed for the agricultural/farming sector show up in the main category of NCS/NBS instead of Agriculture, including farm-soil C sequestration and reduced emissions from N fertilizer usage. If Canada increases beef production, the increased methane emissions from ruminant digestions and manure management will show up in the Agriculture leger, while the increased soil carbon storage caused by increased perennial forage production will show up as NCS/NBS. In this recent paper from ECCC and AAFC scientists, soil carbon sequestration from the associated increased perennial forage production was calculated to offset nearly 2/3 of methane and manure emissions caused by Canadian beef cattle.
  • If farmers increase input usage to increase crop photosynthesis, any added emissions from increased input usage show up as Agriculture; increased soil carbon storage shows up as NCS/NBS.
  • To expand on this point, I see future difficulties in two areas – one being journalists, NGOs and public researchers doing quick Internet searchers to see “what Canadian agriculture us doing to reduce GHG emissions” without being aware of the major NCS/NBS component. Another concern involves international ag emission comparisons based on use of data listed in GoC documents like the 2030 Emissions Reduction Plan.
  • I would welcome increased efforts by AAFC and others in the GoC to explain, clarify and (hopefully) correct this source of confusion. A change in reporting to include all of agriculture under Agriculture in future reports would be far better, though I don’t see that as likely, given the dominant role of ECCC and its many eNGO friends. (Any weakening of the scope of NCS/NBS is likely to be viewed unfavourably by them.)
  • Also welcomed would be considerably more detail on how all the money committed to GHG reduction in agriculture, since late 2020, is to be used.

Please notify me of any errors – typos (which are my specialty) and other errors – at . Thanks.

2022 Update: What are the Realistic Opportunities for Reducing Greenhouse Gas Emissions in Canadian Agriculture?


About a year ago, I posted an analysis about why and how Canadian agriculture might reasonably reduce greenhouse gas (GHG) emissions. Because of some notable events and advancements during the past year, I am providing this update. I start with an overview of what’s happened internationally and then focus on soil fertility and nitrous oxide (N2O) emissions, and on soil management and soil carbon/CO2 sequestration. There are promising opportunities to reduce GHG emissions via the former, but enthusiasm likely exceeds reality with the latter.  I add a very small amount at the end on agricultural methane and on developing trade in GHG agricultural credits.

Intergovernmental Panel on Climate Change, and Glasgow Conference

  • Working Group I (WG I) of the Intergovernmental Panel on Climate Change (IPCC), responsible for summarizing scientific information on the physical basis of climate change, issued its Sixth Assessment report in October 2021. The WG I full report is about 1300 pages and will likely be read in its entirety by very few people. However, a 40-page Summary for Policy Makers (SPM) is available (accessible here). The SPM is dominated by discussion on models of expected temperature changes using various assumptions about future greenhouse gas (GHG) emissions. A middle-of-the-road WG I model predicts a global average temperature about 2.0 to 3.5 C higher in 2100 compared to the average for years 1750 to 1800. A weakness in the projections, in my view, is uncertainty in the extent to which the measured global temperature increase of 0.8 to 1.3C to date (two-thirds certainty) since 1750-1800 is the result of planetary heating caused by GHG gases in the lower atmosphere, and/or cooling by emissions of particles and other gases into the upper atmosphere. WG I says it is two-thirds certain that human-caused GHG emissions have been responsible for a 1.0 to 2.0 C increase in average temperature to date, with upper-atmosphere contaminants causing a cooling of 0.0 to 0.8 C. Despite that uncertainty, WG I concludes, “It is unequivocal that human influence has warmed the atmosphere, ocean and land.”
  • The other big international event in 2021 was the United Nations Climate Change Conference in November, commonly referred to as COP26. One conference outcome was a series of long-term government commitments for achieving zero net GHG emissions several decades in the future. Because of the vagueness in how these reductions are to be achieved, there are many doubts about the value of these promises by politicians. (The Government of Canada has yet to meet any of its previous commitments for GHG reductions.)
  • Most media reporting, so much of which focuses on abnormal (often labelled “extreme”) weather events, has not been very helpful in advancing public understanding of the fundamentals of climate change. Climate change is usually measured by scientists as changes in 30-year averages and related long-term trends, not short-term peaks. However, media exuberance has probably been effective in encouraging many people to demand that governments ‘do something.’

Nitrous Oxide (N2O)

  • Discussion about total Canadian agricultural GHG emissions can be found here and here. About 42% of what are counted as Canadian agricultural GHG emissions using IPCC calculation protocol involve direct emissions of N2O from soil. Half of that comes from the application of synthetic nitrogen fertilizer (mostly) and farmyard manure. Further, the release of N2O from Canadian soils fertilized with synthetic N has increased by about 60% since 2005 – the biggest increase over that interval among all identified Canadian agricultural sources of GHG. The Government of Canada in a broad policy statement on climate change and GHG in December 2020 announced a 10-year commitment to reduce N2O emissions from fertilizer usage by 30% . (See also here.) This has prompted lots of discussion on how to do this and the implications of doing so. A national media campaign by Fertilizer Canada promoted a message that implementation of the 30% reduction would mean a $48 billion loss in Canadian farm income over eight years (see here and here).
  • The IPCC GHG calculation protocols offer three routes for countries to calculate emissions from N2O usage (or indeed any GHG emission source). These are labelled Tier 1, 2 and 3, with a higher number meaning an increasingly detailed calculation procedure. The Tier 1 calculation for N2O involves the simple assumption that every kg N fertilizer applied to soil results in an emission of 0.01 kg of N2O-N. The 0.01 ratio is termed an emission factor. With Tier 1 calculation, the only way to achieve a 30% N2O reduction is to reduce total domestic N application by 30%.
  • Canada uses a Tier 2 calculation procedure (see Section A3.4.5,Part 2, Government of Canada National Inventory Report, accessible here), which to date has been based largely on a review of literature published by Rochette et al (2008). The current N2O Tier 2 calculation for Canada divides Canada farmland into three main zones (two for the Prairies and one for Ontario and Quebec) each with a base emission factor, and then further into 405 ‘ecodistricts.’ Within each ecodistrict, the emission factor is adjusted for differences in predominant soil texture (higher emission factor for fine-textured soils), topography (higher for lower-lying soil), and the calculated ratios between use of manure versus synthetic N fertilizer. There are other adjustments for use of irrigation, for N2O emissions during the non-growing season, for use of biosolids, land in summer fallow and no tillage. (No tillage means more N2O release in the East compared to conventional tillage, and less in the West – a function of the effects of soil moisture.)
  • Recent follow-up papers by Rochette et al (2018) and Liang et al (2020) suggest changes are likely in Canada’s Tier 2 emission factors for N2O. However, there is no specific reference in these papers to adjustments for timing of N application, differences in fertilizer placement, or the use of urease and nitrification inhibitors – i.e., three-quarters of the ‘4R’ N2O reduction strategy promoted by Fertilizer Canada.
  • An obvious farm management option is to reduce total N application rate per acre/ha. Research and extension articles by Dr. Weersink, De Laporte and colleagues at the University of Guelph have indicated that N application rate could be reduced most years without notable loss in income. (See here and here.) However, long-term research by Dr. Bill Deen and colleagues at the Elora Research Station (see here) shows that the optimal N rate can vary by 70% from year to year. And some of the analyses by Weersink and De Laporte involve using crop yield data for a given year to calculate the amount of N that should have been applied to the same crop a few months earlier. That’s only possible in computers. Also, calculations based on small plot data generally don’t take into account within-field variation in N fertility needs for those farmers (i.e., most) who apply a single rate of application for the whole field.
  • Variable rate N application could address both problems. Data from US research (see, for example, here, here and here) shows that optimum N requirement decreases with increasing soil organic matter amount. The extra N in high OM parts of the field comes from greater ‘mineralization’ (OM breakdown) which releases plant-available N. The concept can be difficult for a farmer to grasp – more N fertilizer needed in ‘poorer’ parts of the field (‘poorer’ meaning lower yield expectation because of lower soil OM content) – but it may be a means for farmers to reduce average rates without visible N deficiency symptoms in greater-need parts of the field. The US data suggest a reduction in N applied of 15-20 kg N/ha for every 1% increase in percent SOM.
  • Another equally large problem is the seemingly impossible task of adjusting springtime N application rates for subsequent annual differences in corn yield (usually the result of differences in summer rainfall). Banger et al (2020) express the challenge well: “Results of this study further suggest that farmers need to adjust N rates depending on the weather in a growing season.” But how?
  • To this end, analyses summarized by Nasielski and Deen (see slides 10 to 12) show high correlations between seasonal rainfall from mid-June to mid-July and optimal seasonal N need. It should be possible to vary the rate of N application with split applications, with the second half of the split occurring after July 15 – and with less N applied in July when rainfall is below normal during the previous month. Data from Nasielski et al show that the late split application should not affect crop yield compared to normal June side-dress application.
  • The most important practice for reducing N2O emissions from fertilizer application without hurting yield is the use of urease and nitrification inhibitors. Data such as those summarized by Dr. Tom Bruulsma here show that the use of these inhibitors alone could reduce N2O emissions from fertilizer usage by 20 to 40 percent. See also, this paper from Wagner-Riddle’s team at the University of Guelph. Hopefully, future Canadian policy designed to reduce N2O emissions from fertilizer usage will include this technology, even if the effect does not show up in Tier 2 NIR calculations as they exist now. In the United States, the Environmental Protection Agency has indicated that it is considering including inhibitor reductions in future versions of its Tier 3 estimates of N2O emissions associated with soil fertility (see here). While N2O emissions are very important for GHG calculations, they are generally too small to have implications for farm profitability (reference here).

Soil Carbon Sequestration

  • There continues to be a major gap between the opinion of many farmers and agronomists that cover crops increase the organic matter content of Canadian soils, and hence are valuable for carbon sequestration – versus the scarcity of supporting data. For example, Morrison and Lawley, 2021, in a survey of Ontario cover-crop users, found that 68% of the 530 Ontario famers who responded to survey on cover crop usage considered cover crops to be an important method of ‘building soil organic matter.’ In contrast are data reported by Chahal et al (2021) for 36-year and eight-year research studies at Elora and Ridgetown ON, respectively, showing zero effect on soil organic matter (SOM) content from the inclusion of red clover in corn-soybean-wheat crop rotations.
  • Van Eerd, Chahal and colleagues have two adjacent long-term cover-crop experiments at Ridgetown featuring horticultural crops, and have reported substantial increases in SOM. See, for example, this statement in a recent issue of Ontario Grain Farmer magazine, “So far, we have found cover crop species had 11 — 22 per cent greater soil organic carbon storage when compared to the no cover crop control”. The published research data are here. However, these researchers also collected soil samples from the same plots at the same time and sent them to a lab at Cornell University for analysis. Those data published here show a range of increased SOM from minus 3% to plus 11% increase across cover crop treatments and tests, with the 11% increase in one test – the only one statistically significant – being a comparison involving cereal rye cover. There were no significant differences with the use of oats or oilseed rape alone as cover crops. Despite this discrepancy between data sources, the overall numbers do support their conclusion that cover crops can increase SOM in a horticultural crop rotation. With some horticultural crops, the length of the cover crop growing season is substantially longer than with corn or soybeans. However, this explanation does not explain the lack of a SOM benefit with red clover seeded into winter wheat in early spring.
  • Part of the differences reported for effects of cover crops on SOM may involve differences in definition. The most common international definition is this from the Soil Science Society of America, “A cover crop is defined as a close-growing crop that provides soil protection, seeding protection, and soil improvement between periods of normal crop production.” However, a broader definition (see, for example, here) is used sometimes in Western Canada, “A cover crop is grown to cover the soil, at times when the soil would otherwise be left bare.” This would mean ‘green-manure crops’ (crops grown by themselves for the full season) grown to replace summer fallow and perhaps supplying some summer/autumn grazing would be classed as cover crop. While summer fallowed ha are far fewer in number now in Canada compared to years past, I note that nearly half of the respondents to a survey of Prairie farmers by Morrison and Lawley (2021) involved cover crops where no other crop was grown the same year. Finally, an even broader definition seems inherent in this statement from the Ontario Cover Crop Strategy, “[Cover crops are] plants seeded into agricultural fields, either within or outside of the regular growing season, with the primary purpose of improving or maintaining soil quality.” This would seem to include all green manure crops and even multi-year forage crops (eg., perennial legumes grown in ‘ley’ years to accumulate soil nitrogen reserves on organic farmers)  Hence, the extent to which cover crops increase SOM likely depends on definition.
  • For more discussion on the uncertain value of cover crops for increasing SOM, check here, here and here. Doubts about the value of cover crops for increasing SOM do not extend to their other proven benefits. These include reducing soil erosion, improving rainfall penetration, creating deep soil channels for improved drainage and crop root penetration, storing soil nitrates during off seasons when they might otherwise cause off-site pollution, and, in the case of legume cover crops, fixing atmospheric nitrogen (extensive review here).
  • The Government of Canada announced in its 2021 federal Budget the creation of a new $200 million Agricultural Climate Solutions program. One of the three target areas is expanding cover crops as a means of sequestering soil carbon. The rational for doing so, explained here, is based on a relatively small number of Canadian measurements, several of which involve green-manure crops. I would love to be proven wrong, but must respect available research findings, and am skeptical that this expenditure will result in much C sequestration. I am not opposed to encouraging expanded cover crop usage because of all of the other contributions to farm well-being as listed above. (Note that a February 22 news release from Agriculture and AgriFood Canada provides more detail – $183 million to be distributed via agreements with 12 Canadian agricultural organizations – with more information to come in the weeks ahead.)
  • Debate continues on the value of no-tillage in increasing SOM. This benefit is quite consistent in data from the Prairie Provinces (references here). As a result, no-tillage is recognized in calculations of Canada’s soil carbon sequestration in National Inventory Reports (see reference above). However, the data are far less consistent for Ontario and east; typical results often showing yield reductions with no-tillage – primarily because of cooler spring soil temperatures, especially for corn – and no improvement in SOM. (Extensive discussion can be found here.) However, Shi, Drury and colleagues at Agriculture and Agri-Food Canada, Harrow ON, found no yield reduction and a 12.5% increase in SOM after 16 years with the use of pre-plant ‘zone tillage’ (aka ‘strip tillage’) in a 21-cm zone centering on each corn row. This subject requires more research but may provide a means for extending Western Canadian-type SOM benefits to ‘partial no-tillage’ for Ontario and provinces east. It’s worth emphasizing, too, the importance of deep soil sampling when assessing the true SOM benefit from no tillage, given that research almost always shows that no tillage increases the SOM in near-surface soil, but reduces it at depth.


  • I’ve little of value to add on methane from ruminants other to than to applaud progressing strategies for reduced methane production using feed additives and genetics. I note that Verra, a major US carbon credit certifying organization, has initiated steps to issue ‘carbon credits’ for using methane-reducing feed additives (reference here).

Trade in Carbon Credits

  • This is a rapidly developing marketplace, with the potential for major economic benefit to farmers employing new practices to sequester soil carbon and/or reduce GHG emissions. However, it also represents potential danger in that cash paid for miscalculated benefits may need to be paid back at some future date – even decades into the future. Here is a great review and analysis by the Environmental Defense Fund in the US.

Thank You

Many people have contributed to the information and/or thinking expressed above (though I alone take responsibility for errors and omissions). I thank Dr. David Burton, Dr. Tom Bruulsma, Dr. Inderjot Chahal, Dr. Bill Deen, Dr. Aaron De Laporte, Dr. Ray Desjardins, Dr. Craig Drury, Dr. David Hooker, Ken Janovicek, Dr. Joshua Nasielski, Caleb Niemeyer, Greg Stewart, Dr. Laura Van Eerd, Dr. Claudia Wagner-Riddle, Dr. Alfons Weersink and others whom I’ve neglected to mention.

Please notify me at if you spot errors – typographical and other – in this posting. Thanks.

A Brief History of Corn in France: How the Church Suppressed Corn Expansion for More than 250 Years


A little over 45 years ago, equipped with not much more than strong curiosity, a list of contacts and my inadequate high-school French, I spent 3 weeks visiting corn researchers, farmers, and the Association Générale des Producteurs de Maїs (AGPM) in France. At that stage in my career I had spent 10 years in corn research and agronomy in Canada and the United States. But I had come to realize that the Canadian growing season for corn is actually more similar to France than most of the United States. It was time to learn more from our cross-Atlantic colleagues.

That trip was highly rewarding and four years later, I spent additional weeks there.

Not only did I experience an agriculture and corn culture notably different from that in Ontario, I was also seeing a French corn industry – as I realized years later – in the midst of major change.

I also met Jean-Pierre Gay, a corn geneticist/breeder and agricultural historian, who later gave me a copy of his new book entitled Fabuleux Maїs, histoire et avenir d’une plante, published by AGPM in 1984. It’s a history of corn from its very beginnings in Mexico to the early 1980s in France.

I was busy at the time, and still had only a rustic ability in French, so the book was skim-read briefly and put on a shelf. Now, almost 40 years later, I’ve had time to read Gay’s book completely – parts of it several times – and what I’ve discovered is one of the best chronicles of corn history I’ve ever read.

Fabuleux Maїs is full of details on the beginnings of corn in Meso-America, and its rapid establishment throughout many parts of Europe and Africa after Columbus’s journey in 1492. The history of corn in France is especially intriguing.

The book is available from Amazon, but only in French and only in non-electronic form (no option for Google Translate). So, for the benefit of those with no French language skill or who lack the time to read the full 296 pages, I’m providing the following brief summary. I’ve also added a small amount on corn advancement in France after the book was published (or at least the part with which I am personally familiar).

Corn Comes to Europe

Metallic gold was what the early Spanish explorers sought during their visit to the New World in 1492 and the years immediately thereafter. But the real gold they discovered is what we in English-speaking Canada and the United States call ‘corn’ – and ‘maize’ in other Anglophone countries, ‘maїs’ and ‘maiz’ in French and Spanish,  Zea mays by scientists, and by dozens of other names around the world. Apparently, the original name in Europe might have been ‘mahiz,’ a name used by Cuban indigenous people who were likely the first corn growers that Columbus encountered.

(I am using the term ‘corn’ in this article for the simple fact that that’s the name with which I’m most familiar, and probably the term used by most of my readers, as well.)

Columbus brought corn back to Spain, and there is good evidence that white Caribbean flint corn was grown near Seville in southern Spain in 1494 AD.

Though Seville is far south in Europe, it’s still well north of Cuba, and given corn’s  high photoperiodic sensitivity, it would have been very late in maturity (and quite tall). But that it was a success is shown by the rapidity with which its culture expanded through much of Mediterranean basin, and into Balkan countries to the north and east a few decades later.

Though the details are beyond the scope of this article, corn was also spreading rapidly elsewhere at the time. There is record of it in Indonesia in 1496, with early arrivals in India, The Philippines, South-east Asia and China). Portuguese traders and slavers were responsible for the first spread into Africa about 1550.

Gay says in Fabuleux Maїs that the original Caribbean flint corn was infused relatively quickly with imported corn varieties from Mexico including shorter-season varieties from the highlands, but no details are provided.

Interestingly, one of the first European visitors to what’s now known as Canada and the United States was a Frenchman, Jacques Cartier, who in 1535 travelled as far west present-day Montreal and reported encounters with corn-growing people along the St. Lawrence River including well east of the present Quebec City. However, there is no record of Cartier bringing back corn seed to grow in Europe. Of note, those St. Lawrence River farmers were all gone when Samuel de Champlain and other French explorers arrived again after 1600. (They are believed to have been members of the Mohawk and/or Onondaga nations who by 1600 were located near Lake Champlain and lands to the south and west.)

The spread of corn through the Old World was remarkably rapid though with few or no formal records kept of details, so that there was later confusion as to its origin. Corn was often referred to, in various languages, as ‘Turkish wheat’ with that country assumed to have been its original home. Some authors claimed there are references to corn growing going back to the ancient Egyptians and also in the writings of Homer (Greece) and Pliny The Elder (Roman). The assumption of an Old World origin was not that uncommon for a century or more to follow Columbus’ travels.

Corn Arrives in France

2022-02-04 16_36_13-MAP OF FRANCE CITIES - France map with cities and towns

Map of France

With France, the story is a little different. The first record of corn there dates to 1523 in the Basque country, near the towns of Bayonne and Biarritz and in nearby French Béarn (extreme southwest, near the Atlantic, a few km from Spain). But the spread beyond there was slow and largely through the rugged poorer farmlands to the east and north-east of Toulouse.

There is also a lot of confusion about the early progress of corn growing in France as it was commonly referred to as millet, and confused with the grain of African origin with the same name – and sometimes with sorghum too. Thus, unless accompanied by a drawing or some reference to grain size, there is no way of being sure which species is being referred to in sporadic records from the south of France for a period of 100-150 years or more.

Corn did enjoy early popularity in extreme southwestern France. There is a record of 1000 tonnes being exported from this area to Spain in 1774. It formed about 70% of the local human diet – commonly accompanied by pellagra, a deficiency disease caused by the low content of the amino acids lysine and tryptophan in grain corn. (Indigenous American nations were subject to the same disease though generally countered it with co-consumption of beans, meat and fish.)

But beyond very southwestern departments, corn was very slow to become a common crop in most of France.

Corn did spread as far as Alsace in 1637 where it was called, interestingly enough, “Welsch korn.” There is some evidence (though not in Gay’s book) that this was the result of a second early entry of corn into southeastern France from northwestern Italy.

But French corn production remained tiny. The reasons for the slow spread were several:

One was that corn was not considered healthy to eat – perhaps linked to the pellagra problem, but also the generally impoverished and unhealthy condition of most people who lived in what was then regarded as a very backwards part of France. Unless humans were forced to eat corn, it was generally reserved for livestock feeding, with humans opting for foods produced from wheat (mainly) but also other small-grain cereals.

The more productive lands for grain production in France are generally in the west, north-central and north, where wheat and similar cereals reigned supreme.

By far the biggest obstacle seems to have been the church and a practice called ‘la dîme.’ (I don’t know the equivalent English name, if there is one.) La dîme was an historic practice by which farmers (mostly tenant farmers) paid a set amount per unit of land area to the church for the right to grow various crops. There were fixed per-ha rates for wheat, rye, barley, all the common food crops, but none for the ‘new’ crop corn. In return, the church discouraged the production of corn in various ways. The discouragement included spreading misinformation about its unhealthiness and association with poverty.  Because much of the land was owned by large landowners who wanted to be assured of ultimate salvation, many of them inhibited corn growing on rented lands.

There were efforts made to pay the church amounts in lieu of the dîme. And though this might seem like an obvious solution, efforts to introduce a dîme for corn did not prove popular (one reason being that some farmers and landlords saw corn as a legal – though frowned-upon – way of avoiding the payment to the church).  The dîme was one reason why those in agriculture many have deliberately confused corn with millet and sorghum  – though I am not sure of the historic status of true millet or sorghum as dîme-requiring crops.

The result was that peasant farmers were allowed, generally, to grow a small amount of corn without hassle, but when it came to represent a substantial portion of cropped land, a visit from a church official was inevitable.

I have not seen information as to which ‘church.’ Though French Protestant  Hugenots were still common in southern France for part of that era, I assume the dîme was a Roman Catholic practice.

My understanding is that the practice of dîme payments pretty much disappeared during the French Revolution in 1789, but the die was cast: grain corn was not considered a proper crop to grow in much of France – much less to eat – for up to four centuries after its first arrival in 1523. That continued well into the twentieth century.

Hence, land surface area devoted to corn did not grow consistently. According to author Gay, in 1840, 532,00 ha of corn were grown in France. But by 1943, that had declined to 217,000 ha, with half of that grown in two (out of a total of 96) French departments in the extreme southwest.

Beginning of  the Modern Era for Corn in France

An important event occurred in 1930 in Pau, France – the Congrès International du Maїs, organized by a railroad company, la Compagnie des Chemins de Fer du Midi. (Why a railroad company sponsor? Author Gay says he does not really know.)

The Congress that emphasized the revolution on corn breeding then underway in the United States was a major success. Two years later, a corn genetics/breeding research station was established at Saint-Martin-de-Hinx (near Bayonne), and two years after that, in 1934, the Association Générale des Producteurs de Maїs (AGPM) was founded, based at Pau.

Although breeding efforts at Saint-Martin-de-Hinx continued through World War II, most other Congress-related activities including further development of AGPM stopped. AGPM was revived again in 1947 and a second international AGPM-led congress was held at Pau in 1949. This time the emphasis was mostly on hybrid corn and its success in the United States.

As a result, the production of hybrid corn and number of planted ha of grain corn grew rapidly, reaching 300,000 ha in 1948-50, with an average yield of 1.8 t/ha, to 600,000 10 years later and an average yield of 2.8 t/ha. (For those who think in bushels and acres, that’s about 45 bu/acre.)

The hybrids grown initially were exclusively of US origin, which led to two issues: 1) they were very late in maturity and adapted only to extreme southwestern departments, and 2) they were American.

There were many debates about whether corn grown from US hybrids was safe for the soil or to eat. There were complaints that US was actually foreign territory for corn and that emphasis should be on corn varieties from what locals considered to be its locally assumed ‘centre of origin’ – the Basque country and nearby Spain. There were also debates on whether the higher productivity with hybrids was a good thing. Hybrids took more skill to grow (less vigorous at the beginning than local open-pollinated varieties and required more fertilizer), and produced more corn than some farmers needed. (“After all, farmers have been able to grow enough feed for their animals using the older varieties,” some said. “Why change?”)

Nevertheless, corn continued to expand – at least in warmest parts of the country. The hybrids were too late in maturity to be grown on the better France farmlands generally in the north, north-central and western parts of the country.

The first use of the herbicide, simazine, occurred in 1958 and this also encouraged corn expansion, especially with other herbicides to follow.


Rugged farmland (and small town) north-east of Toulouse near where the flint variety, Lacaune originated

Major breakthroughs occurred soon after World War II. The first involved an obscure open-pollinated flint variety called Lacaune developed by farmers in the high-elevation (and comparatively cool) department of Tarn northeast of Toulouse. Successive generations were grown at high plant densities, resulting in a population of corn that was cold hardy, early maturing and tolerant to high plant densities.

Some seeds of Lacaune found their way to the INRA research program at Versailles (INRA stands for Institute National de la Recherche Scientifique), where a few generations of selection resulted in two inbreds, F2 and F7, that were released in 1946-47. The single cross, F2 x F7, was a flint hybrid with the same characteristics as Lacaune and good yield in its own right, but also of high heterotic vigour when crossed with early-maturing dent inbreds from the United States.

INRA released several flint-dent hybrids beginning in 1957, starting with INRA 200 and followed by INRA 258. Both were double-cross hybrids involving pairs Wisconsin inbreds and their single-cross, crossed with F2 x F7 (or F7 x F2, female parent listed first). INRA 200 and 258 were early enough in maturity to be grown as far north as Paris – permitting corn to mature for grain on these better French soils.

The Famous Hybrid, LG11, and Even Better Ones to Follow

This, in turn, led to the release of hybrid LG 11 in the late 1960s, by the cooperative Groupe Limagrain, based at Clermont-Ferrand. LG11 had the same Wisconsin-inbred/F7 x F2 parentage. LG 11 proven to be immensely popular and, along with the INRA hybrids, was responsible for a major expansion of corn production into the Loire River region of France, and northward, beginning in about 1970. Though I don’t have precise data, my understanding is that LG 11 may have represented 40% of French corn hectares during the mid 1970s.

I grew LG 11 myself and some other early-maturing French hybrids during the late 1970s in cooperative trials across Canada and France. We were interested in how the two groups compared in different environments. The flint-dent French hybrids generally had more cold tolerance in spring but were notably slower to dry-down in autumn. Some of these French hybrids were promoted for use on Canadian farms but the slow dry-down proved to be a major obstacle to farmer acceptance. The cold hardiness was attractive in Canada, but not so much as in Western Europe. (Canadian spring weather goes from cold to hot quite quickly, compared to the long, cool springs common across the Atlantic.)

The success of LG 11 in France prompted other French and American companies to consider related ventures and what followed were a number of joint ventures including France Maїs, a partnership with Pioneer based near Blois on the Loire River, and RAGT, a partnership with DeKalb, based at Rodez, north of Toulouse. One of the major developments was the hybrid Dea, a single-cross between a North American dent inbred and F2, released by France Maїs/Pioneer in 1981. Dea represented a large improvement in productivity (yield and stalk quality) and was widely popular, securing a major presence for Pioneer in France as well as continued expansion of corn production to the north.

One company that did not partner much with any North American partner was Groupe Limagrain. It continued to expand in France and then into North America. The former King Grain corn program based at Paincourt Ontario, marketer of Pride Seeds in Canada, is now part of AgReliant Genetics owned by Groupe Limagrain and Germany-based KWS.

(One of my most pleasant memories was that of serving as external examiner for a doctoral thesis defense of a Limagrain agronomist at the Université Clermont-Ferrand in about 1982. I don’t remember much about the thesis but I sure do remember the party to follow.)

My history stops here because I am not as familiar with the details of French corn development after I left the University of Guelph and joined the fledgling Ontario Corn Producers’ Association (OCPA) in 1983-1984.

It’s worth noting that my experience with AGPM was one of the reasons why I was so keen on the establishment of OCPA.

My impression is that French hybrids have become more dent like, and less flinty, with time – driven no doubt by a desire for faster dry-down in autumn and greater use of North American germplasm in corn breeding programs.

And French corn hectares have continued to grow, reaching 2 million ha in 1988 though with a gradual decline to about 1.5 million since then. The decline may be partly attributable to the inability of French farmers to grow transgenic hybrids with genes added for insect control and tolerance to glyphosate herbicide (very valuable in no-till agriculture).

I’ll close my brief history with an anecdote. When I visited France in 1975, I spent one late-August evening meal with an INRA corn breeder and his family in Montpellier. Before we left his research plot area for the day, he went to the very back of the research field and collected some ears of sweet corn – well hidden by taller corn nearby. At his home, he carefully closed the shutters before they boiled the ears for eating. It sure tasted good, but they didn’t want any neighbours to know we were eating corn.

Now you can buy sweet corn for eating anywhere in France. I saw several recent tweets from France promoting ‘popcorn’ (same word in French as English).

And I haven’t seen anything of late from the Catholic church condemning corn eating and corn farming.

Times change.

I express my deepest appreciation to Jean-Pierre Gay and his outstanding book Fabuleux Maïs, histoire et avenir d’une plante, which is the source of 99% of the information presented in this article. Thank you also to Mr. John (Jack) Watson of Des Moines Iowa, formerly of Pioneer International, who established the Pioneer/France Maïs corn breeding program near Blois and provided some information on the post LG 11 era. I thank l’Association Générale des Producteurs de Maїs for sponsoring Mr. Gay’s book and for its leadership in corn advancement.


Le Mont-Saint-Michel, Normandie, not a corn picture but one of my favourite views in France

Do Canadians Really Lose or Waste 58% of Food and Food Ingredients? A Critical Look at the Calculations Says No

20211017_134748Food wastage has become a hot topic with everyone from the United Nations to numerous NGOs decrying the size of the loss and promoting opportunities to do better. Though I have been critical of some of these reports which usually don’t include any analysis of what a major reduction in food wastage would mean for the entire food system (smaller processing and retail industry sales and employment, as examples), I agree that less wastage would be beneficial in many ways.

There have been some excellent studies. To cite one, Dr. Mike von Massow and colleagues at U Guelph measured the quantity and composition of weekly food wastage for 94 Guelph households that had at least one child. An average of about 3 kg of food per week was found in their household garbage or 230 kg worth an estimated $936 per year. About two-thirds was fruit and vegetables. If an average household had three people, that’s about 80 kg and $312 per person/year. If multiplied by 38 million Canadians, that’s about 3 million tonnes and $12 billion – with almost all of that going to landfills or composting.

The United Nations estimates than 17% of global food is lost or wasted, 14% of that post harvest, and about 11% of the 17% in households. Reference here. If Canadians consume about 26 million tonnes of food per year (reference here), the measurements of wastage by von Massow et al equate (albeit calculated crudely) to about 12% of that – essentially the same percentage as the UN figure.

Though I’ve not provided more references, my impression is that other studies also show food wastage percentages to be in the range of 10-20% with the majority of this being perishable fruits and vegetables.

So it was a real surprise to me when I saw a couple of high-profile reports from University of Guelph researchers in past months stating that Canadians lose or waste about 58% of all food and food ingredients. That includes this recent publication from researchers whom I hold in highest regard.

The 58% figure seemed away too high for me, and inconsistent with the other reports. I decided to dig deeper.

It turns out that it comes from a study done by the consulting company, Value Change Management Inc (VCMI), for Second Harvest, a food bank in Toronto. There are two publications – a shorter summary written by Second Harvest staff – and a 118-page full technical report written by VCMI. Both are accessible here. The following comments pertain mostly to the latter.

Two key tables in the technical report are these (FLW means food loss and wastage, HH means household and HRI means hotels, restaurants and institutions):

2021-09-08 08_50_38-Window

2021-09-08 08_54_50-Window

From Table 3.2 we see that, unlike in the other studies, most of the loss (21.89 million tonnes, or nearly two-thirds of the calculated total 34.89 million tonnes of annual food loss and wastage) involves field crops – mainly grains and oilseeds. It’s not fruits and vegetables as in other studies. And only about 5 million tonnes (2.76 + 2.38), or 15%, is at the consumer level.

Table G enlarges on this, showing that a total of 65% (5% + 8% + 30% + 6% + 5% + 10% +1%) of field crops are loss or wasted in the food chain process.

The technical report is rather vague as to where all these numbers come from. But, it appears that in the case of grain corn that I am most familiar with – they have first taken a crude estimate of the percent of total Canadian grain supply used directly for feed – 60% for corn (also 30% of wheat and 80% of barley) using base figures rounded to the closest 10% provided by this feed industry source. Then they have assumed that all the rest of the corn is used to manufacture food. Hence, they assumed that the difference in weight between the 40% of non-feed corn (adjusted for imports and exports) minus food products produced from corn is all loss or wastage. It’s true as they’ve noted that Statistics Canada does not segregate annual data on corn usage for food and industrial processing, but it seems very incorrect to assume that it’s all (or even mostly) food. And if the same was assumed for usage/processing of all other grains and oilseeds, the error could be huge.

To check further, I had a telephone conversation with two principal researchers at VCMI and it appears that this is only partly right. In the case of soybeans, for example, where about 80% of processed weight ends up as livestock protein feed, they did not assume the 80% is loss or wastage. But in the case of corn, it looks like they did. Other grains are partly in between.

For corn, the 40% for processing produces non-food products like fuel and industrial-grade ethanol, carbon dioxide (which has a surprisingly strong market demand despite greenhouse gas concerns), paper coatings, protein byproduct feeds and more. This is not food loss or wastage.

The authors take some pains to differentiate between planned (or unavoidable) losses and unplanned (or avoidable) losses. See the red columns in Table 3.2. However, this does not really correct for the original flaw. And in the higher-profile material released from this study (see the adjectives like “staggering,” “depressing” and “enormous” used by Second Harvest), it’s the 58% total figure that gets most play.

In summary, I believe that 58% wastage or loss is grossly misleading.

There are three other questionable assumptions in the report that I’ll mention briefly.

  1. In the production of processing crops (good examples being tomatoes and fresh peas in Ontario), it is standard practice to plant more crop than is needed for processing in an average year. This is to ensure that there is still enough crop for processing in years with poor growing conditions – or years when high temperatures mean crops in the field reach and pass the harvestable stage (eg., peas, sweet corn) too quickly for the processing plants to accommodate. Without this allowance for excess in average or better years, there would not be enough crop to meet processor needs in unfavourable years. There are processes in place – for example, crop insurance – to ensure that farmers are compensated financially in years when their crop is ‘bypassed.’

There is, at best, a vague reference to this practice in the technical report. In the summary written by Second Harvest, it states ‘thousands of acres of produce are plowed under due to cancelled orders’ which likely includes this practice. Labelling this as wastage or loss seems misleading as it implies that a societal goal should be its reduction. One could obviously eliminate it if farmers were only to plant enough crop to meet processor needs in better-than-average years. But that would mean plant shut-downs and insufficient food supply in all other years – hardly an appropriate or responsible solution.

  1. The technical report makes an estimate of the value of the food loss or wastage by dividing total value of food produced/marketed in Canada by total tonnes of food. Hence, all wastage and loss is assumed to be worth $4,351 per tonne (the figure is about 10% higher for losses in the HRI sector). That includes agricultural product losses at an early stage of processing and lower-value byproducts like ethanol, paper starch and livestock feed protein. That does not seem realistic.

 Also, the report implies that if this calculated wastage and loss did not occur – meaning that total food supply were    100%/(100% – 58%) or 2.4 times (240%) as large as at present – the value of Canadian food would be 240% higher too. This ignores obvious questions like “Who would eat the additional supply?” It also ignores the basic economics of supply/demand balance.

To the suggestion that it could be mostly sold for export, my response is “At $4351/tonne, I don’t think so.”

  1. My third point seems trivial by comparison, but in the technical report it refers to a 10% loss in onion production attributable to moisture loss during conditioning for storage. However, the same process occurs with several grains including grain corn. Corn dried from about 24% moisture at harvest to 15.5% or lower for storage also endures a weight loss of at least 10%. If the onion calculation was applied to field crops, the calculated Canadian loss and wastage percent would be even higher than 58%.

In summary, I’d recommend that reviewers and others not use 58% as a meaningful estimate of loss and wastage in the Canadian food system. The United Nations figure of 17% seems more appropriate. The 17% loss is still in serious need of reduction, for a world faced with feeding 10 billion by about 2050, but it’s not nearly the 58% calculated in the Second Harvest reports.

A History of the Ontario Corn Producers’ Association, 1982 – 2009

For me, this story starts at a farm meeting at Lindsay Ontario in January 1983. As a University of Guelph-based corn agronomist, I had become convinced Ontario corn farmers had major need for an effective organization to represent them. I had seen what equivalent organizations had accomplished in France, Manitoba and various US states, and wondered, why not the same for Ontario?

Marmora-area farmer Doug Brunton spoke at that farm meeting about fledgling efforts to create just that, and I soon became involved in speaking out in support of the new group at other farm meetings – usually as backup to Dunnville-area farmer, Max Ricker, who chaired the founding committee.

But the story actually begins much earlier. The Ontario Corn Producers’ Association (OCPA) was the culmination of about 40 years of unsuccessful efforts until then to create a marketing board – or marketing board-like organization – to represent Ontario grain corn growers. (More on that history here.)

Details of the initial process leading to OCPA are a bit sketchy, but the process seems to have started with an ad hoc corn marketing committee of the Ontario Federation of Agriculture (OFA) in 1978. The OFA made a formal request to the Ontario Minister of Agriculture and Food for the creation of a marketing board or equivalent in September 1979, supported by a petition signed by 1500 farmers, and another in April 1980, but both requests were denied.

Then in March 1982, another OFA-led committee developed a proposal for a corn association with no marketing board powers but which could administer an Advance Payments for Crops program under the authority of Agriculture Canada, provide information to farmers, and represent them on public issues involving corn. A formal proposal for creation of the Ontario Grain Corn Producers’ Association – later dropping the word, ‘Grain’ – was developed and presented to the Minister of Agriculture and Food, Dennis Timbrell. He supported it and OCPA was created formally on December 29, 1982 with five founding directors, Max Ricker; Doug Brunton; John Cunningham, Thamesville; Seldon Parker, Woodville; and Martin Schneckenberger, Morrisburg.

This achievement was followed by a hectic period of selling individual farmer memberships at $25, election of founding regional directors, and a founding convention on March 28, 29 in Toronto. Doug Brunton was elected first president. The initial OCPA office was with the OFA in Toronto and OFA staff researcher, S. Verraraghavan, was the first secretary. I became unpaid secretary-treasurer in July, replacing ‘Verra,’ though I was still employed full-time in the Department of Crop Science, University of Guelph.

In September 1983, OCPA leased an office and hired its first two paid employees, Judy Sweeney as office manager and Don LeDrew as program coordinator. Don was hired initially to develop and run an Advance Payment for Crops program for grain corn (interest-free money loaned to farmers at harvest time, to be repaid when the corn is later sold or fed; loans guaranteed by Agriculture Canada – later Agriculture and AgriFood Canada). Don quickly assumed other management responsibilities.

Terry switched formally to a one-quarter-paid time with OCPA in mid 1984 and then full-time with OCPA in January 1985 with various position titles including that of executive vice president.

OCPA was initially funded by annual memberships of $25 plus lots of volunteer effort. But Minister Timbrell announced at the OCPA annual meeting in March 1984 his intention to introduce check-off funding for the 1984/85 grain corn marketing year and an interim grant of $60,000 to cover some costs in the interim. The Grain Corn Marketing Act was introduced in the Ontario Legislature and approved in three readings, all on the last legislative sitting day of June 1984. OCPA had good political support from all three Parties in the Legislature. A mandatory-but-refundable-upon-request checkoff of 10 cents per tonne of corn sold to commercial corn buyers was initiated on October 1, 1984. There was no producer vote, which led to initial concerns that the request-for-refund ratio would be large. But to my knowledge, it never got as high as 1%.

The early-to-mid 1980s were a very difficult time for North American corn farmers, the result of plunging grain prices and extremely high rates of interest on borrowed money – all made worse by a preceding decade of mostly high grain prices, high inflation and interest rates often below rate of annual inflation. This combination had encouraged farmers to increase their debit obligations to finance expansion – making the financial blood bath to follow that much more severe.

From the beginning OCPA was focused on grain farm income. An early achievement involved finding an error in a federal calculation of whether Ontario corn farmers were eligible for a federal grain stabilization payout on sales in 1982/83 marketing year sales. The resulting corrective payment of $4.48/tonne went a long way in establishing the credibility of OCPA among corn growers.

The insolvency of Niagara Grain and Feed of Smithville in autumn 1983 led to a major campaign by OCPA that resulted in affected farmers recovering almost all of their lost funds for corn deliveries and sales to the elevator. That exercise led directly to the creation of the Ontario Grain Financial Protection program – a combination of buyer licensing for financial reliability and the building of a compensation fund using a checkoff on commercial grain sales. This program continues to work well in Ontario.

OCPA played a major role in the creation of two ‘Special Canadian Grains Programs’ in 1986 and 1987 to compensate Canadian grain farmers for a portion of financial losses experienced as the result of a then-intense international subsidy and trade wars. OCPA also initiated a successful corn countervailing duty trade action on Canadian imports of most forms of grain corn from the US from 1986 through 1991, which both boosted corn farm income in years when Canada was a net corn importer, and also highlighted the injurious nature of US grain subsidy programs at the time. The Canadian countervailing duty was very effective in reducing the damage to Canadian corn growers for five years. When it was eliminated by a World Trade Organization decision in 1991, the rationale for its existence had diminished substantially.

Likely because of this experience, OCPA became an active member of advisory committees to the Government of Canada during the development of the Canada-US Trade Agreement, then NAFTA (North American Free Trade Agreement – including Mexico) and then the Uruguay Round of the World Trade Organization negotiations.

Crop insurance reform was another early priority for OCPA. The organization playing a major role in reforms that led to better coverage and, especially the ‘floating price option’ that meant that farmers were compensated at close to harvest market price when they lost crops because of insurable weather perils. This was of major benefit in encouraging pre-harvest corn delivery contracts.

OCPA played a major role in the creation of several successive national grain farmer income protection programs that followed in the two decades after 1990.

In addition to farm income support/protection, OCPA was very active on other fronts:

A meeting of Ontario farm groups chaired by OCPA in 1986 led to the creation of what became AGCare (Agricultural Groups Concerned about Resources and the Environment) with leadership provided on safe pesticide usage and the establishment of Environmental Farm Plans in Ontario. A formal request from AGCare led to the establishment of Ontario’s Ontario Pesticide Education Program with its mandatory training and certification of farmers for pesticide usage. AGCare and OCPA played major roles in the early approval of genetically enhanced crops for use in Canada. OCPA lobbied aggressively for early Canadian approval of usage of genetically enhanced ‘Bt’ corn hybrids.

AGCare was headquartered in the OCPA office, with OCPA providing free rental and secretarial service for a number of years. AGCare later became part of Farm and Food Care Ontario.

OCPA played a major role in government approvals for and industry development of a biofuel industry in Canada. Terry Daynard served as an early president of the Canadian Renewable Fuels Association, to be succeeded in that position in 1989 by Lambton County farmer, Jim Johnson (also an early OCPA president).

OCPA was driven by a marketing philosophy that, while Canadian corn exports were important, more important were opportunities to increase the usage of home-grown crops to manufacture new food and industrial products. This led to strong organizational interest in other bioproducts such as bioplastics, and in support for domestic corn processors who produced feedstocks for those innovative companies.

OCPA was also active in communications. A monthly newsletter to members was one of its earliest contributions and this led to a partnership agreement with Cash Crop Publications in Delhi, Ontario and the transformation of its former monthly Cash Crop Farming into the Ontario Corn Producer magazine (now known as the Ontario Grain Farmer magazine).

OCPA was one of the first Canadian agricultural organizations or businesses to use a fax machine (in 1986 or 1987) and this followed by purchases of fax machines for all directors. I well remember the discussions with other farm groups attempting to persuade them to also “get faxes” so we could send paper copies of material to them immediately rather than by day, or multi-day, courier service as was the norm at the time.

The same happened with email and Internet. OCPA and its directors all made this transition in the early 1990s and the OCPA web site won early Canadian national recognition (about 1995) for its innovative approaches.

OCPA was one of the earliest farm groups to hire a full time communications coordinator with his time being spent mostly on ag awareness activities as well as promotion of OCPA objectives such as biofuels.

OCPA was an active supporter of farm coalitions playing major roles in the early creation of the Ontario Agricultural Commodity Council (actually a transformation from an earlier OFA committee), the Agricultural Adaptation Council, ACC Farmers Financial, the Grain Growers of Canada, the Ontario Field Crops Research Coalition and others. These activities were largely the result of initiatives of OCPA directors and delegates, with support by OCPA staff.

I left OCPA in early 2002 and am not as familiar with association activities from then until formal amalgamation eight years later with Ontario soybean and wheat groups to form the Grain Farmers of Ontario. That transition occurred over several years with the three groups sharing a common office location but separate organizations at 100 Stone Road West, Guelph from 2005 to 2010. OCPA continued to be very active on farm income support programs and championed another (this time unsuccessful) trade action against imported US corn. OCPA was part of the coalition of farm groups responsible for creating, in 2007, the Risk Management Program currently used for farm income support in Ontario.

OCPA offices beginning in September 1983 were at 292 Speedvale Avenue West, then 190 Nicklin Road (September 1986), then 90 Woodlawn Road West (September 1991) and then 100 Stone Road West (September 2005). Formal amalgamation of the three groups, and the end of the Ontario Corn Producers’ Association, occurred on January 1, 2010.

Presidents of OCPA were:

Max Ricker, Dunnville, chair of founding committee

Doug Brunton, Marmora, 1983-1984

Ed Kalita, Eagle, 1984-1987

Cliff Leach, Paris, 1987-1990

Frank Anthony, Limehouse, 1990-1993

Jim Johnson, Alvinston, 1993-1996

Bob Down, Exeter, 1996-1999

Anna Bragg, Bowmanville, 1999-2001

Dennis Jack, Thamesville, 2001-2003

Matt Menich, Vanessa, 2003-2005

Doug Eadie, Ripley, 2005-2007

Dale Mountjoy, Oshawa, 2007-2009

A special thank you to Brenda Miller-Sanford, member of the staff of both OCPA and the Grain Farmers of Ontario, for her help in assembling information used in this column.

My Comments on 2021 Report of Intergovernmental Panel on Climate Change, Working Group I


The 48 hr media cycle for the latest IPCC AR6 WG I) report is well past, but for anyone interested, here’s a short column with a few highlights in the Summary for Policymakers that caught my attention. The Summary plus full report are available here,

The Summary for Policymakers is 42 pages long and not that difficult to read for those with some science education.

The conclusions in the report are generally the same as in previous IPCC reports though with greater confidences for stated conclusions on climate change, and narrower projections of future temperature ranges. We’ll have more hot days, fewer cold ones, more intense rainfall events and higher evapotranspiration. Fewer tropical storms but more intense ones.

Global average temperature is now back up to the same peak reached about 6500 years ago. That agrees with what E.C. Pielou reported for Canada in her classic book, “After the Ice Age.” Of interest, Pielou also presented strong evidence that Western Canadian mountain glaciers largely melted at that time; what’s melting now with the current global warming are glaciers that mostly formed after peak temperatures 6500 years ago. (This is not to diminish the significance of present glacier loss to modern society.)

The new IPCC report places more emphasis than before, I think, on the cooling effect of aerosol compounds in the stratosphere (upper atmosphere). IPCC authors are quite confident that average temperature has increased about 1.1C since 1850-1900, but surprisingly uncertain on the extent to which this has been caused by GHG heating in the troposphere (lower atmosphere) and/or cooling by these upper atmosphere aerosols.

This part-sentence in Section A.1.3 is key, “It is likely that well-mixed GHGs contributed a warming of 1.0°C to 2.0°C, other human drivers (principally aerosols) contributed a cooling of 0.0°C to 0.8°C.” (“Likely” means 66% probability.)

This uncertainty also shows up in the IPCC WG I estimate of the warming caused by specified amounts of CO2 released into the atmosphere. In Section D.1.1, authors say, “Each 1000 GtCO2 of cumulative CO2 emissions is assessed to likely cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C.” That’s a 2 1/2 times range in temperature response to given amount of CO2 emission, with a confidence level of just 66%.

IPCC projections on aerosol cooling also merit emphasis. If sulfur dioxide emissions decline with less coal burning and less air pollution, that could mean increased global warming because of less stratospheric cooling.

The net effect of the above, in my view, is some doubt about the precision of the IPCC’s projections of future temperature increases for given future amounts of GHG emissions. This is not to detract its overall message that human activities are causing global temperature changes and changing precipitation patterns compared to what would be expected solely from natural causes – and that a human priority should be to limit these changes to the extent possible while focusing also on adaptation.

I’ve one other comment: The IPCC report features five models of future climate changes to be expected with different levels of GHG emissions. But two of the five involve future rates of CO2 emissions far greater than what are being projected by most credible analysts – i.e., a 50% increase in rate of CO2 emissions by 2050 for one model and a near 100% increase by 2050 for the other. Discussions in the report of future climatic conditions with global warming are based too much, in my view, on these two unlikely models. Dr. Roger Pielke Jr. makes the same point though more eloquently and completely in a column here.

For those seeking more, here is one Twitter thread that I found very helpful: . You should also consider following @Peters_Glen who posts meaningful analyses almost daily. The Breakthrough Institute ( also has published several good articles on climate change, of particular interest to agriculture.

As for what this means for global agriculture and food supply, I offer three conclusions:

  1. Agriculture must devote more effort to technological changes, which reduce or even eliminate net GHG emissions, while still ensuring adequate supplies of nutritious food at reasonable costs for consumers.
  2. Plant breeding and the use of advanced genetic technology, to produce new cultivars more resistant to heat and drought, will be even more important in years ahead.
  3. Cultural techniques to store more water, including soil moisture reserves, from periods of intense rainfall for use during dry periods/seasons will become even more important than they already are.

The Many Unsuccessful Attempts to form an Ontario Grain Corn Marketing Board


Typical Ontario corn crib, circa 1975

This column was published originally in 2005 in the Ontario Farmer and is reproduced here with permission, for the interest and convenience of those interested in Ontario corn history.

Among the mostly forgotten chapters of Ontario corn history are many unsuccessful attempts to form an Ontario grain corn marketing board.  The following description of these efforts is far from complete, but the best I could manage using various written records – often sketchy – and the living memories of individuals involved in the corn industry more than a half century ago.

The Ontario Corn Growers’ Association (OCGA) described in an earlier column was born in Essex County in 1908, in part because of a desire to promote the sale of seed of locally grown open-pollinated varieties, and died within a year or two after the formation of the Ontario Seed Corn Growers’ Marketing Board (OSCGMB) in 1940.  The latter was created to represent growers of hybrid corn seed.  Many of the farmers who were active in OCGA during the late 1930s became initial directors of the OSCGMB. The early history of the OSCGMB is described in Leonard Pegg’s “Pulling Tassels: A history of seed corn in Ontario,” published in 1988.

There was a parallel effort to create a marketing board for commercial grain corn. I know relatively little about the Essex-Kent Corn Producers’ Cooperative Association created in 1940 with Charles O’Brien of Roseland as president.  However, a file in the Archives of Ontario describes how this organization promoted a proposed “Ontario Corn Growers’ Marketing Scheme.” The Essex-Kent cooperative group was created apparently to act as a central selling agency for marketing all commercial grain corn in southwestern Ontario. The group sought single-desk selling and compulsory government grading of all corn. There was major concern over low prices (40 cents/bushel), large harvest-time fluctuations in price, and a view that these were caused by inadequate competition. However, there is no record of a producer vote or widespread support.

Minutes of the Ontario Corn Committee (OCC, more detail here) show that representatives of the Essex-Kent cooperative group met with it in 1943 and 1947, mainly to discuss the importation of US seed corn and seed quality. Darrel Jubenville of Tilbury was a key spokesperson at these meetings.

The Ontario Archives also contain a proposal in 1946 by a group called the Commercial Corn Growers of Ontario to create “Corn Negotiating Committee” which would have the powers to negotiate minimum prices, grade standards, and associated shelling, elevation and handling fees with corn dealers and processors. The proposed membership of this Committee is similar to that of the earlier Essex-Kent cooperative association though the 1946 listing also includes representatives from Lambton, Middlesex, Norfolk, Elgin and Waterloo counties.  The Archives contain copies of a ballot and draft letter to be sent to up to 7000 growers in April 1946. However, I can find no evidence that this mailing happened or that any vote occurred.

Darrel Jubenville and a few other farmers made group representations at various meetings of the OCC from 1948 through 1951.  While they refer to the “association” which they represent, this association is not named in the OCC minutes.

More intriguing are Archive files from 1962 that include a March 6 letter from the secretary of the Ontario Farm Products Marketing Board to Deputy Minister Everett Biggs detailing procedures for a “recent Corn Vote.” The vote supposedly occurred between January 15 and 30 on the question: “Are you in favour of the proposed plan to be known as The Ontario Corn Producers’ Marketing Plan?” The Plan was to “1) provide a voice for growers, 2) develop markets and new uses for corn, and 3) promote corn for Ontario and Canada and ward off the inroads made by imports.” The vote was apparently championed by the Commercial Corn Growers Association led by Armould Mulcaster of Essex, with the support of the Ontario Federation of Agriculture, but was opposed by “The Five County Grain Corn Committee” led by Darrel Jubenville.

I can find no record of results of this vote or any indication other than the letter to Biggs that it even occurred. Certainly, no marketing board structure was created as a result.

In the late 1960s and early 1970s, agitation arose again among corn farmers for a marketing board to address low corn prices, then near $1/bushel. I recall meeting Jim McGuigan of Cedar Springs, then a director of the Kent and Ontario Federations of Agriculture and later the Member of Provincial Parliament for Kent-Essex.  He told me of unsuccessful efforts by himself and many others to generate the support needed for a marketing board.  “They’ll support marketing boards for nearly every other farm commodity,” said Jim in frustration, “but not for grain corn.”

However, because of producer discontent, Bill Stewart, the Ontario Minister of Agriculture and Food, called for a meeting of corn industry representatives to be held at the Ridgetown College of Agricultural Technology in September 1971. I was privileged to be present. (Darrel Jubenville and Mac Best from Fingal were also there representing the Canadian Commercial Corn Growers Association – the last written reference I’ve found to that organization.)

Delegates at the Ridgetown meeting recommended that an Ontario Corn Council be formed. The Ontario Grain Corn Council (OGCC) was officially created by Minister Stewart in December 1971 with Ken Patterson of Middlesex County serving as chairman, and eleven other appointed members. Ken served as chairman until 1986 and during this time the council effected a number of improvements including reduced rail shipping rates and tax incentives for new grain storage.  The council actively promoted improved corn quality and the increased industrial processing of Ontario corn.  It organized several export trade missions and helped create a Winnipeg Board of Trade futures market for grain corn with Montreal being the “delivery point.” (This market ended after about two years because of a lack of business.) Most importantly, the council portrayed corn as a major Canadian crop, and not just a regional grain grown mainly for on-farm feeding – the previous image. The council continued until about 1990 when the Ontario government ended its funding.

Creation of the OGCC did not end the pressure for a producer organization. Indeed, a group called the Corn Producers’ Investigating Committee from Kent County (chaired by Stuart Shaw but with Darrel Jubenville also present) met with the OGCC and representatives of the Ontario Ministry of Agriculture and Food (OMAF) in April 1972 seeking an “Ontario Corn Industry Act” and an associated board to provide much greater regulatory control over marketing and pricing.  This proposal received no support from the council nor Minister Stewart.  Dramatic increases in corn prices beginning in late 1972 were probably why pressure for a marketing board ended at that time.

Finally, in 1979, some corn growers began to work on plans for a new producer organization.  The Ontario Corn Producers’ Association (OCPA) was founded in December 1982.  Passage of the Ontario Grain Corn Marketing Act in 1984 gave OCPA checkoff collection powers, and it persisted until 2010 – then becoming part of the amalgamated group, the Grain Farmers of Ontario. OCPA was created without a producer vote, but with benefit of a refundable checkoff on producer grain corn sales to commercial buyers. It had no regulatory power over any aspect of marketing, only the power of lobbying and rational advice to governments. A more detailed column on the history of the Ontario Corn Producers’ Association will follow.

What are the Realistic Opportunities for Reducing Greenhouse Gas Emissions in Canadian Agriculture?

No-till soybeans planted in between rows of corn stalks

This overview is intended for those in Canadian agriculture interested in using proven, or partially proven, technologies to reduce net greenhouse gas (GHG) emissions through changes in farming practices.

If you don’t want to read further, my conclusions are:  Opportunities look greatest for reductions in nitrous oxide (N2O) emissions. Further reductions in carbon dioxide (CO2) emissions through more usage of no tillage are possible, and the potential to sequester soil organic carbon through increased perennial forage production exists, but it’s questionable that these will lead to sizable futures decreases in national GHG emissions. Cover crops, with a few exceptions, probably represent limited opportunity for soil C sequestration in Canada with our long winter and short off-season growing intervals, but may prove more valuable for reducing spring-time N2O emissions. Future reductions in methane (CH4) emission are dependent on the extent to which promising research on rumen additives can be implemented in practice.

Carbon Dioxide

Let’s start with CO2 because, globally and nationally, it’s the most important of the three major GHG gases.

(The three gases are CO2, N2O and CH4. When GHG emissions are reported as CO2, that means only the one gas, but when reported as ‘CO2 equivalent,’ or CO2e, that means the collective warming potential of all three gases – plus a few more gases unrelated to agriculture that have smaller effects – all weighted for their relative potential to affect global warming. N2O has about 298 times the warming potential of CO2 on a per-kg basis; for methane it’s about 25, calculated as the average 100-year effect.)

According to GHG accounting protocols specified by the International Panel on Climate Change (IPCC), agriculture represents 8.1 % of total Canadian emissions, but with CO2 only representing 4% of that. These stats are as reported by Environment and Climate Change Canada (ECCC) in its latest National Inventory Report (NIR) to the United Nations Framework Convention on Climate Change (UNFCCC). I’ve summarized Canadian data for 2018 here; the numbers for 2019 are virtually the same – ECCC 2019 summary here – entire report available here.

However, CO2 emissions associated with on-farm fossil fuel usage, biofuel manufacture/usage and net CO2 exchanges between farm soils and the atmosphere are not included in the NIR/UNFCCC calculations for agriculture. If these were in, the Canadian net agricultural emissions would represent 8.5% of the Canadian total (calculations here). Even with these additions and subtractions, CO2 still represents a very small percent of total net agricultural emissions.

If we go further and add GHG emissions associated with fertilizer manufacture (mainly N), the 8.5% grows to about 12%, with most of the increase being CO2, but with CO2 still being a relatively small portion of the Canadian agricultural total.

Finally, if the amount of carbon contained in products that leave Canadian farms and are exported were to be included, the total net GHG emission from Canadian agriculture would actually be negative – removal of CO2 from atmosphere exceeding all forms of ag GHG release. But that calculation remains far from IPCC calculation plans, at least as it appears now.

For the following discussion, I’ll focus only on two categories, net GHG exchanges for ‘Agriculture’ as reported by NIR/UNFCCC, and the agricultural soil portion of another category called, ‘Land Use, Land Use Change and Forestry,’ or LULUCF.

The Canadian NIR recognizes three sources/sinks for CO2 in its LULUCF calculations for agricultural soils. These are: land converted to continuous crop production from periodic summer-fallowing, land converted to reduced tillage and no tillage from more intensive tillage, and land converted into perennial forage production from annual crop production, as well as the reverses.

Emission factors for these land-use changes reported in the Canadian NIR are shown in Table 1 (taken from Table A3.5-8 in Part 2 of Canadian 2020 NIR).

Table 1. Effective linear coefficients of soil organic carbon for land management changes (LMC); for the opposite changes – eg., no tillage to intensive tillage – the linear coefficients are negative of the values shown in column 3.

Of the three factors, the largest effect by far comes from a conversion of annual crop to perennial cropping. Unfortunately, the trend in recent years has been more of the reverse – perennial to annual – a result of better prices for annual crops and declining beef production in some provinces.

An increase in perennial crop acres, ideally as part of crop rotations with annual crops, would be very beneficial for soil organic carbon sequestration, but it is difficult to see how this will happen – given increasing public interest in plant-based (that generally means annual-crop-based) alternatives to ruminant meat. A fledgling cash-crop industry is developing in Ontario and perhaps other provinces for the production and export of high-quality alfalfa hay, but the scale is still too tiny to permit conclusions on whether this will grow to represent a significant means for increasing SOC on a national scale.

The shift from intensive to no tillage provides the smallest per-ha annual change. Table 1 may over-estimate the no-till benefit in Atlantic Canada, Ontario and Quebec. Available research data are inconsistent as to whether there is a net positive no-till effect on soil organic carbon in this part of Canada. Research data show a more consistent increase in soil organic carbon with tillage elimination in the Prairie Provinces. But the biggest shift in Prairie crop acreage to no tillage may already have occurred.

A reduction in summer fallowing causes a larger per-ha annual effect than no tillage, but this is largely limited to the semi-arid Prairies where summer fallowing is still practiced to a significant extent – and this benefit declines as the portion of Prairie farm land available for summer-fallow elimination continues to shrink.

It must also be noted that the annual SOC sequestration provided by these changes in land management declines each year as shown below in Fig 1, extracted from the 2020 Canadian NIR. After 20-25 years, about 50% of the total GHG sequestration potential from a change in land management practice has been achieved.

Fig I. Changes in SOC sequestration with time after implementing changes in land management practices (from Fig A3.5-14 in Part 2 of Canadian2020 NIR). The dashed line denotes an annual sequestration of 25 kg/ha of SOC; once the estimated sequestration falls below this, the values are not included in Canadian LULUCF totals.

A popular means of sequestering soil organic carbon may be cover crops – at least as expressed at farm meetings and as featured in ag media of late. A number of global research publications also make this claim. However, in a recent review of the published evidence, I concluded that the likelihood for such is very limited in short-growing-season environments like Canada. There are exceptions – for example, red clover spring seeded into winter wheat, or for some horticultural crops where the off-season available for cover crop growth may be unusually long. Though I’d love to be proven wrong, I personally don’t see cover crops as a nationally significant option for CO2 sequestration. That may be the reason why cover crops are not included in the listing shown above in Table 1 taken directly from the Canadian NIR.

There is a strong alternative opinion to what I’ve expressed above. For one example, see this backgrounder written by the respected Dr. Brian McConkey (formerly with Agriculture and Agriculture Canada – AAFC – and now chief scientist with Viresco Solutions) for Farmers for Climate Solutions (available here, check Chapter 2). Dr. McConkey’s view is that a portion of any organic matter addition to the soil, no matter how small, contributes to SOC enhancement. That includes cover crops which may only produce a few hundred kg/ha of organic matter per season. His perspective may stem from this article written by Dr. Fan and a number of AAFC researchers including Dr. McConkey who conclude, based on computer models, that more organic matter addition to soil automatically means increased SOC content. However, the Fan article includes a series of graphs (Fig 5 in the paper, if you are looking) that predict, based on this perspective and these models, that the SOC percentage in farm soils of Southern Ontario should increase anytime the annual organic carbon addition exceeds about 3-4 tonne/ha.

But the annual organic matter addition to soil with a typical corn-soybean or corn-soybean-wheat rotation is about 12 t/ha – which equates to 5 t/ha (assuming organic matter is 42% C) and yet the SOC content of Ontario farm soils in principal cash crop areas of the province is in decline. See following graph courtesy of Christine Brown, Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), that is based on thousands of soil samples tested in Ontario labs.

There has to be more to SOC enhancement than just more added organic matter (not that the latter is not also important).

This paper containing results of a 10-year, multi-site study in Iowa provides an explanation. While the addition of organic matter including cover crops to soil will add additional organic matter, it can also increase the rate at which soil organic matter is respired – often resulting in no net gain in SOC.

McClelland et al 2020 in a meta-review found that SOC enhancement with cover crops was generally only significant when the annual cover crop dry matter accumulation was 7 t/ha or higher. Many cover crops in Canada produce only about a tenth of that.

In brief, while cover crops in certain situations may increase SOC, it is doubtful that collectively these represent an important opportunity to increase the carbon dioxide sequestration in Canadian farm soils. This is not to detract, at all, from other cover crop benefits, including important reductions in soil erosion.

Nitrous Oxide

The quantity of nitrous oxide (N2O) emitted each year, globally or nationally, is small compared to CO2, but the warming potential of a tonne of N2O gas is about 298 times greater. N2O represents about 5.2% of total Canadian GHG emissions measured as CO2 equivalents, but agriculture represents 76% of that according to the Canadian NIR.

Although some of the agricultural N2O comes from manure storage before field application, about 86% comes from the application of N fertilizers to farm soils, both synthetic N fertilizers and manure. There are some excellent reviews including this one done by a group of researchers at the University of Guelph as well as  this, this, this and this.

The research results are extensive and quite consistent:

  • Increased N application rates mean more N2O loss. Indeed, the simplest IPCC calculation protocol for estimating national N2O soil losses expresses loss as a fixed percentage of N applied. Research suggests that N2O loss actually increases exponentially with N application rate, meaning the last 10 kg/ha of applied N causes the biggest N2O loss on a per-kg basis. There have been numerous agronomic/economic studies of the most economical rate – complicated by large annual variations in both actual N losses and crop yields caused by differences in amount and intensity of rainfall. Rapidly increasing yields over time for some crops – corn and canola are examples – also complicate these calculations. How to provide the additional N without increasing N2O losses?
  • Fertilizer additives that slow the transformation of urea and ammonium forms of N fertilizer will reduce N2O emissions. The literature suggests an average of about 30% reduction with the combined usage of a urease inhibitor (slows urea transformation into ammonium) and a nitrogenase inhibitor (slows ammonium transformation into nitrates) for treatment of urea or UAN (urea plus ammonium nitrate) fertilizers. The reduction is also sizable, though less, with the usage of polymer-coated fertilizers.
  • Partial side-dress application of fertilizer N, as compared to full application of N at or before planting, does not appear to reduce N2O losses consistently as a percent of N applied. But because side-dressing reduces the total N application need, this means a reduction in N2O loss. A lot depends on when intense rainfall events occur relative to time of application.
  • In a recent paper, Eagle and several co-authors from across the North American Corn Belt concluded that N2O losses are more closely related to the difference between N applied minus N removed in harvested crops, than to N application rate per se. This means that variable application rates based on within-field differences in measured late-spring soil nitrate levels or historic differences in within-field yield represent another good option for reducing N2O losses.
  • For a given rate of soil N addition, any practice that reduces soil nitrogen losses for other reasons, eg., reduced ammonia volatilization with fertilizer incorporation or reduced leaching loss of nitrate will often tend to increase N2O losses, so there are management tradeoffs.
  • N2O loss also tends to increase with Increases in soil organic matter content, so a tradeoff once again.

So what does all this mean? With the use of N fertilizer inhibitors, and adding combinations of partial side-dress N application and within-field variable N applications, it should be possible to reduce N2O losses by 30-50% or more with synthetic N fertilizer usage – with the cost for added technology being offset, at least in part, by lower average N fertilizer application rates.

Manure N seems more complicated. IPCC Tier 1 guidelines (the approach countries are to use in calculating GHG emissions when they lack the data or expertise to permit more sophisticated calculations) calculate a lower percent conversion of available N into N2O with manure compared to synthetic fertilizers. However, that is not well supported by North American research results that show that, on average, the two loss ratios are about equivalent. See references cited above.

To that, add the complication that manure is often applied to fields in the late summer or autumn – after wheat harvest, for example – to provide fertility for the crop to be planted the following spring. In provinces/states/countries – like Ontario – with substantial autumn and early spring rainfall, that can mean major N off-season losses via leaching, and N2O emissions.

Data summarized by OMAFRA indicate that 50 to 80% of the N content in late-summer/autumn–applied manure may be lost in off-season months. (The percentage varies across types of manure and whether incorporated or not.)

One solution is to apply manure in spring before or after crop planting but that can be logistically difficult in years with wet springs. Manure additives may reduce the problem though that’s a subject on which I have no knowledge.


Cover crops may sequester limited CO2 in Canada but could be very valuable for reducing early-spring N2O losses.

Cover crops are an opportunity to reduce emissions but this is a source of uncertainty. Research by Dr. Wagner-Riddle and colleagues at the University of Guelph (see publication here, and personal communication) has shown that early spring N2O emissions are significantly lower with a cover crop like winter rye. A substantial portion of the year’s total annual N2O emissions can occur during this short period; the cover crop effect seems to be one of reducing the depth of frost penetration, or maybe the number of early-spring freeze-thaw cycles.

However, other researchers at the University of Guelph hold a different opinion. “Conservation tillage, [and] cover cropping … increase N2O emissions,” state Ashiq et al (2021) as a highlighted conclusion in a recent review. My read of the literature indicates such an unqualified conclusion is probably inaccurate, though it likely reflects any effect of cover crops, if present during the main growing season, in preserving soil moisture and, hence, increasing the likelihood of anaerobic soil conditions for N2O formation.

Non-legume cover crops are well recognized for their value in reducing soil nitrate levels in autumn, and the expectation is that this will reduce the potential for autumn-winter-spring leaching losses. Cover crops may thus reduce the amount of nitrate available for N2O formation in early spring. But if the cover crop dies quickly following late-fall-early-winter frosts, thus releasing nitrates back into the soil profile in weeks to follow, this may mean more nitrate available for N2O formation in early spring – maybe even more than with no cover crop at all. Legume cover crops mean more soil nitrate availability and the potential for more N2O formation, especially at time of cover-crop death.

A very informative meta-review was published in 2014 by Basche et al. They found 29 relevant studies of paired comparisons – cover crop versus no cover crop. Of those, 40% found a decrease in N2O emissions with cover crop usage and 60% found an increase. In general, there was more likely to be an increase in N2O with cover crops when: the cover crop was an N-fixing legume versus grass/cereal or other species; the residues from killed cover crops were incorporated into the soil versus left on the surface; and when N2O emissions were measured during the initial time of cover-crop residue decomposition versus for longer periods of time. The reviewers also state that, to the extent that cover crops reduce nitrate losses from leaching, they will also reduce off-site N2O losses which can be substantial though not measured in any of the 26 studies.

A best option seems to be cover crops that remain fully viable over winter followed by no tillage so as to not incorporate residues. But getting them killed in time to not affect the growth and yield of the subsequent spring-planted crop can be a challenge – again especially in years with above-average spring rainfall. Dr. Eileen Kladivko of Purdue University provides a good discussion on these options here.

Cover crops may ultimately prove to be of much more value in reducing GHG emissions by suppressing N2O formation, than by sequestering soil carbon, but it is difficult to be certain at this time.


The greenhouse gas, methane (CH4), represents a much smaller quantity of global emissions than CO2, but provides a substantially higher ‘warming potential’ per tonne. Unlike N2O and CO2, CH4 has a relatively short half-life in the atmosphere (about 10 years) before being broken down into water and CO2 molecules.  Methane represents about 13% of total CO2e emissions for Canada, according to IPCC-based calculations, of which about 31% comes from agriculture – and 86% of the 31% comes from ruminant digestion. There are a couple of key issues though I’ll spend limited time on them here as they are addressed well elsewhere, including here and here.

Beef cattle grazing. Photo courtesy Dr. Vernon Baron, Agriculture and Agri-Food Canada, Lacombe, Alberta

One involves the fact that IPCC calculations, based on average warming effects of GHG gases over 100 years do not work well for short-lived gases like methane, with its half-life of about 10 years. And based on an improved calculation procedure developed at Oxford University, the true long-term GHG effect of methane should be much smaller than in the numbers submitted by Canada and others in their annual NIR. This is especially true for Canada where methane emissions from ruminant livestock have been in decline for about the last 15 years. However, a related blog with analysis that I posted in September 2020 has generated about zero interest, and I’m not seeing much greater interest in related articles written by those with much stronger credentials and connections. I’m not optimistic that the work from Oxford U will result in any change in calculation protocol specified by IPCC for annual NIR submissions.

One problem is that the improved calculation methodology also applies to methane emissions associated with fossil hydrocarbons. That’s most of the 69% in Canada not represented by agriculture. This includes natural gas pipeline leaks. Politically, few in the environmental/climate-change lobby want to make changes that would be seen to benefit ‘Big Oil and Gas.’

The other issue involves the potential use of seaweed extracts and other rumen additives to reduce methane production. These technologies look very promising though are largely still at the ‘proof of concept’ stage of development. More R and D work will be required before they can be truly classed as a principal solution for reducing GHG/CH4 emissions associated with ruminant agriculture.

From a broader agricultural perspective, any technology that encourages beef/sheep production will also encourage greater use of perennial forage crops in Canadian farm crop rotations – with major benefits to soil quality and C sequestration opportunities.

Scope for Zero Emissions?

The focus of international discussion, at least in high-profile circles of late, is not so much strategies for partial reductions, but rather, for zero net emissions. Nations and corporation are both competing for media attention in announcing their new strategies for achieving zero emissions by 2050 or even sooner. The cynic in me doubts that most of these mean much as they depend on major future use of technologies that are far from proven, and/or calculations based on avoiding future GHG-producing practices (e.g., credits for not cutting down trees or draining swamps). They also depend on a level of political and public support which is not yet apparent.

So what’s the prospect for zero emissions in agriculture? I’m not aware of many attempts by main-stream agriculture to tackle this question but there are a few. I give credit below to two farm/agricultural groups that have attempted to develop/define strategies, even though I think that both have major flaws.

One is the National Farmers Union for England and Wales which, in this document, describes a strategy for achieving zero emissions from agriculture by 2040. The strategy is based in part on a national strategy developed by the Royal Society. In the NFU’s plan to eliminate the current emission total of about 45 Mt CO2e, it proposes to achieve about 25% of that by reductions in direct emissions of CO2, N2O and CH4 from farming; 20% by additional C sequestration in farm soils, fence rows, farm woodlots and wetlands; and about 55% by the  combination of biofuel production/consumption coupled with the storage of CO2 released in ethanol manufacture using  ‘carbon capture and storage’ (CCS) technologies (essentially underground storage of CO2, though the NFU leaves the door open to other CCS options).

It’s a big stretch to assume that either the sequestration or biofuel-CCS goals are achievable, but full marks to the NFU for offering something.

Another report is one done by the Aspen Institute in Colorado for the US Farmers and Ranchers Alliance (USFRA). The report, based in part on an analysis of negative emission and sequestration technologies by the National Academies of Sciences, Medicine and Engineering (it, in turn, based on an earlier report by Eagle et al), projects that US agriculture could reduce net GHG emissions by 147% by expanded use of technologies such as no tillage, cover crops, better grazing methods and use “frontier” technologies now in early stages of development. (USFRA, in a more recent report with the Foundation for Food & Agriculture Research and based on an analysis done by a team led by the Nature Conservancy, states that the potential offset is actually more than 200%, though with much of this coming from the management of new and existing forests on farmer-owned land.)

One problem with both the NFU and the USFRA proposals is that, even if the projected reductions were to be attained, most of them would not be credited to ‘Agriculture.’ Rather, the credits would go to other sectors such as ‘Energy’ (for biofuels) and Land Use and Land Use Changes (for C sequestration).

 Using the present IPCC calculation methodology, one could offset 100% or more of agricultural emissions with soil carbon storage – as in the Aspen-USFRA calculations – and still have agriculture identified as the source of about 8-10% of national GHG emissions as at present.  With the NFU strategy, 75% of the projected GHG reductions/offsets would not be credited to Agriculture.

In brief, while it may be important politically for agriculture to portray that it has plans to achieve zero emissions by mid-century (as the NFU has done), my conclusion is that this is not achievable using even semi-proven technology known today, and especially with current accounting procedures.

Bottom line:

Sizable opportunities exist now to reduce nitrous oxide emissions in agriculture using proven technologies, and with others looking promising – eg., selective use of cover crops to reduce N2O spring-time emissions. The potential for methane emission reduction is promising if new rumen-additive technologies prove feasible. The opportunities for C sequestration appear more limited unless means can be found for more greatly expanded use of perennial forages in farm crop rotations.

An overview of the Farmers for Climate Solution: Who they are and what’s included in their request for $300 million from Ottawa

(This article is targeted mainly to Canadian farmers interested in climate change and greenhouse gas (GHG) emissions linked to agriculture.)

A coalition called Farmers for Climate Solutions (FCS) released its request on February 24 2021 for $300 million in Government of Canada money for a collection of programs to reduce GHG emissions in Canadian agriculture. I’ve reviewed their request and various background documents released at the same time. My comments follow.

First some background. FCS was launched in February 2020. It’s a coalition of some organic groups, the National Farmers Union of Canada (NFU) and some environmental NGOs. It says that it’s farmer-led but the primary leadership seems to come from Equiterre, a Montreal-based NGO.

FCS says it represents 20,000 farmers. What that likely means is that its component members have 20,000 members. It’s appears that the interaction between FCS and other major Canadian farm organizations, to date, has been minimal.

FCS seems to be well funded, backed by some major left-leaning foundations. Its web site and related materials are highly sophisticated and professionally done. Its release on February 24 was matched by a supportive opinion piece the same day in the Globe and Mail. FCS is clearly well connected; not many groups could arrange for that. I believe this is well beyond the expertise of the NFU or any of the organic organizational members.

That said, FCS leaders get good marks for an initiative that is badly needed – how to reduce GHG emissions associated with Canadian agriculture. They have stepped into a space largely left empty, until now, by main-stream Canadian farm groups. (I do note the formation of the Agriculture Carbon Alliance, a coalition of mainstream groups on March 1, 2021; this is a welcome initiative, though starting a full year after FCS.)

FCS created a task force which contains several Canadian scientists for whom I have high respect. And it does appear that the task force played a major role in developing FCS policy. I personally agree with a good portion of what they have stated and proposed. But I also have some major questions about the rationale, implementation processes and omissions.

Here’s a link to the February 24 releases: .

FCS leaders and task force members identified six areas where they feel government money could be best spent to reduce agriculturally related greenhouse gas emissions in Canada. These are as follows:

  • Doing more with less nitrogen
  • Increasing adoption of cover cropping
  • Normalizing rotational grazing
  • Protecting wetlands and trees on farms
  • Powering farms with clean energy
  • Celebrating climate champions

The total ask is $300 million from Ottawa, plus another $115 million from Canadian farmers, for a total cost of $415 million.

Here are more specifics:

Doing more with less nitrogen

FCS has provided a well-written, well-researched background report on factors affecting nitrous oxide (N2O) emissions from soils and the application of synthetic fertilizers (though not manure). The information is very similar to that provided in this report by Dr. Claudia Wager-Riddle, Dr. Alfons Weersink and colleagues at the University of Guelph. The FCS report divides Canadian farmers into just three groups based on assumed adoption of the “4R” strategy for responsible nitrogen management. I found this to be rather simplistic, given the wide diversity of Canadian agriculture and growing conditions.

Based on this report FCS recommends that Canada spend $115 million matched by a similar expenditure by farmers over two years. FCS documentation states that this money will be mainly used to hire a large number of agronomists to educate farmers on better N application procedures, to take a soil sample per farm to test for nitrates at the season end, and to take leaf tissue samples. My understanding is that this is to happen in 2022 and 2023.

However, my personal discussion with FCS indicates that their intent is actually broader with money being used to implement N2O reduction measures as well as just monitoring. That makes more sense to me as I cannot see how end-of-season nitrate testing, per se, will tell much until it has been done for several years and at several locations per farm, given the large variation in measurements expected because of locational and seasonal differences. Soil nitrate levels at season end depend strongly on annual differences in soil organic matter mineralization (conversion to inorganic N), weather and crop yields as well as fertilizer applications. Similar complications apply to leaf measurements of nitrogen content, with the genetic influence being very important.

Interestingly, the FCS analysis and plan resembles in several ways a strategy for N2O reduction that was developed by the Canadian Fertilizer Institute (CFI) 10 years ago. (Link is here.) I understand that this initiative did not proceed because of a lack of financial support by all Canadian governments except Alberta.

Perhaps there is opportunity to connect what FCS is proposing, including its major request for public funding, with what CFI has proposed. To add to that, I cannot see how the FCS strategy can be implemented in such short time frame without close integration with the sophisticated and extended network already existent with regional agronomists – most of them private and most being Certified Crop Advisors (see here and here).

The CFI plan as well as the scientific analysis in the FCS backgrounder both emphasize the value of slow-release forms of N fertilizer including urease and nitrification inhibitors and variable-rate-within-field N applications. That would be an excellent place to target government incentive money in my view. There may also be opportunities to reduce overall N application rates though one needs to be careful of analyses based on older crop data – given how crop yields, especially for corn and canola have risen so rapidly in recent years – and where calculations of optimum rates are based after the fact using knowledge of the weather that occurred during the crop growth season.

Increasing adoption of cover cropping

A background science-based analysis is provided to justify the expenditure of $115 million over two years to provide incentives for cover crop establishment. I am quite happy to see the government spend money encouraging cover crop usage as cover crops provide many benefits. However, I don’t believe that one of those benefits is nationally significant increases in soil organic carbon content (SOC), given Canada’s mostly cool/cold seasonal conditions – especially with the field crops which currently occupy most arable land acreage. My rationale, based on a review of many scientific reports and meta-reviews, is posted here.

With all due respect to the FCS task force members, I don’t think their scientific backgrounder on cover crops is very convincing. It’s in distinct contrast to the discussion on N2O. The FCS backgrounder cites three studies to support its claim that cover crops enhance SOC. I’m familiar with all three. Of them, one shows no statistical difference in SOC between soils with or without various types of cover crops, one states its data cannot be used for conclusions about soil C sequestration because of the lack of soil bulk density data, and the third made up for the lack of bulk density data by using data from other studies, sometimes even on other continents, while also including studies where the ‘cover crop’ was the only crop grown all season. The task force report does note that its estimates are often based on “limited evidence” and “expert opinion.” Core calculations for Canada are based essentially on very simplistic and speculative calculations. But then the report provides a series of quite detailed tables listing sequestration potential for various agricultural zones and crop species, including offsetting N2O emissions – giving the appearance of precision where such is not justified, at least in my humble opinion.

However, to repeat: I’d be happy to see a program providing inducements for cover crop planting. But the proposed cost is rather high – $115 million over two years – and its promise of GHG emission reductions of 2.2 Mt of CO2 equivalent seems highly speculative and unlikely.

I am suspicious that FCS leaders view this as a program to promote cover crops per se. There is an emphasis in the project description to the differential channeling of money on a per-acre basis to small farmers while making sure that the big guys don’t get too much. If your purpose is to reduce GHG emissions then an acre is an acre, and individual farms with large acreages would seem a priority target. But if your goal is some money to every farmer to plant some cover crops, then money per farmer rather than per acre is more attractive.

Normalizing rotational grazing

The request here is smaller – $25 million (but still large – perhaps exceeding the entire research budget of Agriculture and Agri-Food Canada devoted to GHG reduction). The rationale is a mixture of better management of rangelands in Western Canada and introduction of other crop species into managed pastures. I don’t have enough background to judge the potential effectiveness of what they propose. However, I wish their analysis and purview had stretched further, to include the expanded use perennial forages in Canadian cropping programs. The Government of Canada National Inventory Report submission to the United Nations identifies more perennial forages as about the best way to increase SOC content on Canadian crop land. (For details see the 2020 Canada National Inventory Report, Part 2, Table A3.5-8; link is here.)

The FCS report completes ignores broader aspects of ruminant grazing/agriculture on GHG emissions such as methane emissions associated with forage digestion, and methane and N2O from manure. Indeed, the FCS report seems to ignore animal agriculture completely even though it represents about half of total Canadian GHG emissions, at least as calculating using protocols of the IPCC (International Panel on Climate Change, United Nations).

Personally, if I had $25 million to invest in this general area, I would devote it to more perennial forage production and the developing (and exciting) new usage of new feed additives to reduce methane emissions from ruminants.

Protecting wetlands and trees on farms

This item promises a mitigation of 4.1 Mt of CO2 equivalent for an expenditure of $30 million. As I understand it, this is to pay farmers not to cut down woodlots and drain wetlands. The 4.1 Mt is not new sequestration but rather loss which might occur with tree removal and wetland draining.

The rationale is a bit hard to understand from an Ontario perspective in that we already have extensive laws to prevent forest removal and wetland draining (i.e., wet land being land that is water logged for a substantial portion of the year and not just for an extra week or two at time of spring planting). It’s true that these vary significantly across municipalities. However, I would argue that an expanded regulatory approach makes more sense nationally, rather than what would need to be continual payments to farmers to prevent destruction. $30 million would not go far in protecting all existing woodlots and wetlands – ideally grasslands too – on Canadian farms and ranches

Note this recommendation from FCS is in addition to the $3 billion that the Government of Canada committed to tree planting in its GHG policy announcements in December 2020.

Powering farms with clean energy

An expenditure of $10 million over two years for an unstated GHG benefit.

The money would be spent for retrofitting 100 diesel tractors per year and use of electric-powered tractors on small farms.

All modern diesel farm tractors have highly efficient emission control systems which outsiders (including farmer owners) are prohibited from doing much more than changing the oil. More usage of electric tractors will come but it’s not clear how this $10 million investment in Canada will make any difference.

One of the biggest opportunities for reducing farm tractor fuel consumption is via reduced or no tillage. That is not mentioned here. I understand why this might be a sensitive subject for FCS with its organic farm membership, and for whom frequent tillage is the norm. But better to focus on how to get organic farmers to till less – or not at all – and even feature technologies which discourage tillage usage like the use of glyphosate for vegetation control – rather than avoid the subject in the FCS report. To be fair, I note that options for reducing tillage are one of the current priority goals for several Canadian organic organizations.

Most critically, this section of the FCS report completes ignores biofuels and the Clean Fuel Standard (CFS) announced by the Government of Canada in December. A calculation that I did using data published in the Government of Canada National Inventory Report of April 2020 indicated that the use of biofuels now means a reduction of 6 Mt CO2 equivalent per year for Canada, with more expected with CFS implementation (analysis here). That’s more than any of the six strategies proposed in the FCS document.

Celebrating climate champions

The FCS are requesting $5 million to provide awards to “showcase and amplify the voices of farmers who are charting the path for sector-wide change.” I am a bit nervous about this as I could see it being very political. There is a strong bent towards organic farmers in photos and mini-bios in the February 24 documents. Of course, that’s not surprising since this is an organic/NFU/Equiterre led initiative. But who chooses the farmers, and what might be the criteria – low emissions per acre where organic shines according to some published analyses – or low emissions per unit of food produce where organic is generally inferior?

I think the government could probably find better ways to use $5 million to reduce GHG emissions in agriculture. My vote would go for credible scientific research.

What did they miss?

To add to – and emphasis in some cases – what I’ve stated above, I believe the report has some notable voids. These include:

  • Reduced tillage/no tillage. The Government of Canada National Inventory Report on national GHG emissions highlights the value of no tillage agriculture for enhancing SOC. The benefit is much clearer and better documented for the Canadian Prairies than for BC and provinces east of Manitoba, but research data from the University of Guelph demonstrate that this benefit can be substantial for certain soil-crop combinations in Ontario too. I expect the same applies in Quebec and Atlantic Canada. Granted the annual benefit decreases with time as SOC increases, but the same applies for any other method of soil C sequestration (including cover crops to the extent that they provide this service). Current Canadian National Inventory Report statistics say that reduced tillage now means about a 4 Mt CO2 equivalent reduction in Canadian GHG emissions per year. (For more detail, see Table 6-9 here.) That’s larger than any item in the FCS list.
  • Livestock-related emissions. Reductions in GHG emissions through feed additives and manure management. About 30 Mt of CO2 equivalent emissions now occur because of ruminant metabolism and manure gases according to the National Inventory Report. There are good opportunities for reductions.
  • Great use of perennial forages in Canadian cropping, including opportunities for cash-crop production and marketing of crops like alfalfa. Several Ontario farmers including a farmer cooperative are already marketing high-quality forage produce in Asia.
  • Biofuels, building on the base outlined in the new Clean Fuel Standards of the Government of Canada. Biofuels mean about an annual 6 Mt reduction in CO2 equivalent net emissions currently. The potential is larger.

Next steps

The Farmers for Climate Solutions and its task force members are to be congratulated for their initiative in emphasizing the importance of strategies to reduce GHG emissions with Canadian agriculture and for drafting a proposal for steps forward. A logical next step would be for either FCS to engage with the 90%+ of Canadian farmers and farm sectors who are not part of the coalition to identify practical means for moving forward including opportunities not identified in the February 24 documents. Or an alternative is for main-stream agricultural groups to use what FCS has proposed as a base for developing their own proactive programs for reducing net GHG emissions.

Do Cover Crops Increase Soil Organic Carbon Content? What do the Meta-Reviews Say?


I’ll start with a definition: I think most agriculturalists take ‘cover crop’ to mean a crop grown in the same year as a primary crop such as a harvestable grain or horticultural crop, and that’s what’s assumed in this article. As noted below, some authors also include crops grown alone for the full season, solely for soil quality enhancement.

Current enthusiasm within agriculture in cover-crop usage is well placed. These crops provide clear benefits in protecting soil from water and wind erosion, providing end-of-season livestock feed, enhancing biodiversity, supplying significant quantities of legume N fertility for use by subsequent crops, and removing nitrates from soil at the end of the growing season (though the fate of nitrates thereafter often remains uncertain).

In addition, major attention is being placed on the potential for cover crops to sequester photosynthetically fixed carbon dioxide (CO2) as soil organic carbon (SOC). This includes discussion on possibilities of paying farmers for doing this.

There have been many research trials completed and several meta-reviews published. This column contains a review of what the meta-reviews say individually and collectively – and what it means for agriculture and net greenhouse gas emissions, especially in a northern climate like Canada.

This article is written primarily for an agricultural audience interested in more depth than generally found in media and agricultural ‘extension’ reports, but less than in found in scientific papers. My column has not been peer reviewed although I have checked analytical details with several of the authors cited below.

I’ll start with my conclusions: The evidence is convincing that cover crops often mean more SOC. This benefit is largely proportionate to how long the cover crop grows, how much cover-crop organic matter is produced, and the average annual temperature of the location. A measurable effect is much less likely when the season of growth is short, e.g., when cover crops are seeded after longer-season harvestable crops and/or when the off-season consists of many months of frozen winter. Most authors assume that more SOC with cover crops means increased carbon sequestration, which is probably true in many cases. But the other possibility is reduced or no loss of soil organic matter when cover crops are present, as compared to soil with no cover crop.

That said, notable weaknesses are common in many of the research summaries, including:

  1. Reports based very few years of cover cropping (sometimes only one).
  2. The inclusion of data from experiments where the ‘cover crop’ was the only crop grown for an entire season – and, hence, not really a cover crop by the definition stated above.
  3. The inclusion of experiments measuring percent SOC or soil organic matter only, with no data provided on soil bulk densities especially for cover-crop treatments in the studies. Procedures have been developed for estimating the missing bulk-density values, but these generally introduce sizable errors.
  4. Different sampling depths within or among experiments – range from 2.5 cm to more than 100 cm (though few below 30 cm) – often with simple calculations used to ‘standardize’ to a common depth.

In addition, with one exception which included Chinese literature, none of the reviews included research reports written in languages other than English.

 I’ll refer to these in turn as we look at the results of the various meta-reviews. I should emphasize in advance, that all of the reviews represent a huge amount of work, with authors making major efforts to adjust for weaknesses and inconsistencies in the data sources used. I am most appreciative of that. But at the same time, it’s fair to examine their conclusions in light of how the limitations are addressed.

Now to the specifics.

Eagle et al (2012) of the Nicholas Institute for Environmental Policy Solutions, Duke University, published Greenhouse gas mitigation potential of agricultural land management in the United States: A synthesis of the literature, which includes a chapter called Use winter cover crops. Thirty one field studies were examined with a calculated average annual soil organic carbon gain equivalent to 1.3t/ha/year of CO2 (range -0.2 to 3.2) or 0.35 t C/ha/year. However most of the data referenced in this review came from California and southeastern states. There were six comparisons from states further north, three from Iowa where the cover crop treatments actually caused a slight reduction in rate of soil organic C accumulation and three from Michigan with gains ranging up to 1.83 t/ha/year of CO2. The Michigan studies were comparisons of an organic rotation of corn-soybeans-wheat plus cover crops with conventional corn-soybeans-wheat grown without cover crops. When I checked publications/web-sites, cited in these publications as providing more details on methodology, I was unable to find some key details on organic practices used, specifically the source of N fertility. Was the fertility provided by manure or other organic amendments? I don’t know. Hence, I suggest viewing the Michigan results with caution.

Eagle et al also refer to a study from Maryland in which the percent organic matter was higher in a cover crop treatment; they did not include this study in their calculation of mean effects because there weren’t data on bulk density and quantities of soil organic C per unit soil surface area. A summary table published by Eagle et al includes three model calculations and one “expert opinion,” all projecting more SOC with cover crops.

In essence, the Eagle et al review shows consistently more soil organic C with cover-crop usage in southern states, but an uncertain-to-zero benefit in the US Midwest.

Poeplau and Don (2015) published Carbon sequestration in agricultural soils via cultivation of cover crops – a meta-analysis, with the analysis involving 30 studies, 37 sites and 139 plots. The studies were in 11 countries, including Canada and the United States, and across four continents. Number of treatment years ranged from one to 38 and sample depth from 2.5 cm to 120 cm though with only three studies having samples “below the plough layer.” They calculated an average rate of soil C accumulation in cover-crop treatments, compared to plots without cover crops, of 0.32 + 0.08 t/ha/year of organic C. This paper and this quantity have been cited many times in other publications in support of statements that cover crops increase soil organic carbon.

For no other apparent reason other than I’m Canadian, I chose to check details of the four cited studies which were from Canada. They are:

Campbell et al, 1991, Effect of crop rotations and cultural practices on soil organic-matter: microbial biomass and respiration in a thin black chernozem. Can. J. Soil Sci. 71, 363–376. A 30-year study in Saskatchewan

Curtin et al, 2000.Legume green manure as partial fallow replacement in semiarid Saskatchewan: effect on carbon fluxes. Can. J. Soil Sci. 80, 499–505. A nine-year study in Saskatchewan.

Hermawan and Bomke, 1997. Effects of winter cover crops and successive spring tillage on soil aggregation. Soil Tillage Res. 44, 109–120. A one-year study in British Columbia.

N’Dayegamiye and Tran. 2001. Effects of green manures on soil organic matter and wheat yields and N nutrition. Can. J. Soil Sci. 81, 371–382. A five-year study in Quebec.

Of the four studies, three (Campbell et al, Curtin et al and N’Dayegamiye and Tran) all involve ‘green-manure crops’ grown without any other crop for the growing season and not the definition of ‘cover crop’ given at the beginning of this column. I did not check the other 26 cited studies in this review, but it is quite possible that there are additional ‘green-manure’ studies of the same nature included in the analysis by Poeplau and Don.

A second concern for me with this review is that only 30% of the cited studies contained data on soil bulk density. The authors estimated bulk density values for the other 70% using the graph below copied from their paper. It is based on collective data from the 30% of experiments with bulk density data across all countries.

Poeplau and Don 2021-02-17 09_52_01-Window

Ignoring the one outlier value (which seriously distorts the R2 and p calculations), the line looks like a reasonable fit for the other data. That notwithstanding, the values for bulk density predicted by the graph still appear to have a range of at least +0.05 g/cm3 for a given percent C content. For a soil horizon that is 22 cm deep and about 1.5% SOC, this range in bulk density equates to 3.3 t/ha of organic C, or about 10 times the predicted average accumulation rate of 0.32 t/ha/year advantage for cover-cropped plots.

A third unease for me involves the process used to standardize all organic C measurements to a depth of 22 cm using average measured or predicted bulk density for the assayed horizon – thus mathematically ignoring the normal tendency for SOC concentration to decrease with depth. One might argue a more sophisticated transformation process is not warranted given uncertainties introduced by the bulk density estimates. But it is still another source of imprecision.

In summary, in my view, results of the analysis by Poeplau and Don are sufficient to indicate that cover crops often mean a higher soil C content, but not nearly enough to merit a conclusion of a rate of gain of 0.32 + 0.08 t/ha/year.

As part of an extensive 2019 report called Negative emissions technologies and reliable sequestration, the National Academies of Science, Engineering and Medicine in the United States included a short section recommending cover crops as a means of sequestering soil carbon. However, it only cited two references, Eagle et al (2012) and Poeplau and Don (2015), the two reviews discussed above.

Mcdaniel et al (2014) published a meta-analysis entitled, Does agricultural crop diversity enhance soil microbial biomass and organic matter dynamics? It involved 122 publications with 454 observations. The review featured additional crops inserted into monocrop cultures or simple rotations, and a substantial number of the studies (I don’t think the authors don’t say exactly how many) involved cover crops. About two-thirds of the studies were from North America and the rest distributed globally. Because only 19% of the studies included measurements of soil bulk density to permit the calculation of soil organic carbon content per unit land area, Mcdaniel et al reported only the soil organic carbon concentrations. Because soil samples within individual studies sometimes came from different depths, Mcdaniel et al converted these to an average depth per experiment with no weighting for changes in bulk density with depth. (For their rationale, see Johnson and Curtis, 2001.) There was no adjustment to a common depth across studies.

Mcdaniel et al concluded the inclusion of cover crops increased the soil organic carbon concentration by 8.5% relative to plots with no cover crop. This was a much greater effect than for all other crop rotational comparisons combined in their analysis. The relative SOC boost with cover crops increased with increases in average annual temperature across the various research locations.

The authors defend their use of percent soil organic carbon (i.e., as g/g x 100%) instead of the use of soil organic carbon stocks (t/ha) by the presentation of an appendix graph showing no significant relationship between “% change from monoculture” and soil bulk density. It’s based, I believe, on observations from the 19% of surveyed studies that had bulk density data. Their assumption is in disagreement with the graph presented above from Poeplau and Don showing a trend for bulk density to decline as percent SOC increases.

If bulk density declines as percent SOC increases, this means changes in t/ha of SOM with cover crop addition would be expected to be less than the measured changes in percent SOC.

Kaye and Quemada (2017) in a paper entitled, Using cover crops to mitigate and adapt to climate change. A review, concluded that “Cover crop effects on greenhouse gas fluxes typically mitigate warming by ~100 to 150 g CO2e/m2/year” with “the most important terms in the budget [being] soil carbon sequestration and reduced fertilizer use after legume cover crops.” Their conclusion on carbon sequestration is based largely on the analyses done by Eagle et al (2012) and Poeplau and Don (2015), which are discussed above.

Norris and Congreves (2018) in a review entitled, Alternative management practices Improve soil health indices in intensive vegetable cropping systems: A review, identified 60 studies where various practices had been used in attempts to improve soil health. They selected 22 of these studies, 11 involving cover crops, for a meta-analysis. The meta-analysis revealed no significant relationship between the presence or absence of cover crops and SOC. (It is assumed that SOC is expressed as a concentration rather than t/ha or equivalent in this review, though I don’t believe the authors actually say so.)

Abdalla et al (2019) published a review entitled, A critical review of the impacts of cover crops on nitrogen leaching, net greenhouse gas balance and crop productivity. Using the Web of Science data base they chose 106 studies involving several key words including, ‘cover crop,’ ‘soil organic carbon’ and ‘SOC.’ The range was global but most studies were from the United States/Canada, Europe and China. The objectives of this meta-analysis included the dynamics of soil nitrogen as well as carbon. For questions about SOC, the authors selected the 47 studies containing data on SOC in t/ha (or equivalent) or the combination of percent SOC and bulk density so that SOC in t/ha could be calculated. The authors adjusted SOC data to a standard depth of 30 cm based on an assumption that SOC decreases with depth at a rate of 2.14% per cm of depth. The rationale for that transformation comes from research by Jobbáy and Johnson (2000). While there is good research showing that the rate of change in organic C content with soil depth is not constant (tillage has a large effect on rate of change; see here for example), this adjustment is likely superior to the assumption of no change with depth to 22 cm in the analysis by Poeplau and Don.

Abdalla et al concluded that across all studies, cover crops increased SOM significantly with a certainty of P<0.001. However, this table copied from their paper, shows no statistically significant relationships at all.

In every grouping in their summary table (legume cover crops, non-legume cover crops, mixed and total), the average change in SOC is less than the standard deviation. It’s essentially the same for total greenhouse gas emissions including nitrous oxide.

In my view, the Abdalla et al paper lacks strong evidence that cover crops enhance soil organic C content.

Bai et al (2019) published Responses of soil carbon sequestration to climate smart agriculture practices: a meta-analysis. They selected 417 peer-reviewed papers studying the effects of biochar, reduced tillage and cover crops on soil carbon concentration. Of those, 64 papers featured cover crops with half of those done in the United States. On average across all studies, cover crops increased SOC concentration by 6% – though less but still statistically significant when the growing season was cooler. Although the authors don’t comment on this finding specifically, one graph in the review paper compares the cover crop effect for the 258 paired comparisons involving irrigated agriculture versus the 25 that were just rain-fed. For the latter, cover crops produced no significant change in SOC concentration. The authors state they did not calculate SOC sequestration for cover crop treatments because of the absence of bulk density data.

Jian et al (2020) published A meta-analysis of global cropland soil carbon changes due to cover crop which involved 131 studies and 1195 comparisons. Sixty percent of the studies were from the United States and Canada with the rest spread globally. The authors included papers written in either English or Chinese. Several sources were used for identifying studies including the references cited in the Poeplau and Don paper. Because of that, and the fact that ‘green manure’ was used as a search word, I assume that the studies used included some with crops grown solely for soil quality enhancement for the entire season but not harvested.

Fifty percent of the studies included measurements of soil bulk density, 21% had bulk density data for the check treatment only – in which case the cover crop treatments was assumed to have the same bulk density – and 29% were studies where an estimate of bulk density was made by Jian et al using the same procedure as used by Poeplau and Don (see above).

Jian et al did not attempt to standardize the data to a common soil sample depth, but just divide the results into two categories, those with measurements up to 30cm in depth and those from deeper depths.

The authors calculated an average soil organic carbon increase of 0.56 t/ha/year with cover crop (including some green-manure) crop usage, compared to the no-cover-crop check treatments. The pattern was generally consistent across crops and crop rotations, but with greater SOC enhancement for clay soils versus those with medium and course texture – and only for soil samples collected at or above 30 cm of depth.  The authors found a statistically significant trend for cover crop SOC enhancement to decrease as the mean annual temperature of the location became cooler and the latitude increased (i.e., for places like Canada).

The cautions I’d have with this review involve the inclusion of some studies with full-season cover crops/green-manure crops, and bulk density estimates made using data on SOC concentrations.

McClelland et al (2020) published results of a meta-analysis entitled Management of cover crops in temperate climates influences soil organic carbon stocks: a meta‐analysis. It involved 40 studies and 181 observation. The studies were mostly from the US and Europe (many from Italy), all from between 23.5 and 66.5 latitude (northern or southern hemisphere). They only used studies where they had reliable information on soil bulk density – although sometimes sourced from external sources – at least for the check treatment. All calculations of soil organic carbon content, expressed as t/ha or equivalent, were standardized to a common depth of 30 cm using the Jobbáy and Johnson (2000) technique described above for Abdalla et al.

The authors calculated an average increase in SOC with cover crops of 1.11 t/ha across all studies, compared to no cover crops. They found the greatest differences when cover crops: provided continuous year-round cover or were early-autumn planted and terminated before winter; with no-till cropping versus conventional tillage; when the above-ground cover-crop biomass accumulation was highest; when soil clay content was higher; and when grown in what they termed subtropical and tropical environments. In total, for studies from locations in temperate environments, there was no statistically significant increase in SOC with cover crop usage. A close relationship was found between the time duration between cover-crop planting and termination dates and the enhancement in SOC.

McClelland et al found that SOC accumulation, compared to no cover crop, was substantially higher for tests/plots accumulating more than 7 t/ha/year of above-ground cover crop biomass compared to those accumulating 7 t/ha/year or less.

One strange result was that authors found no relationship between the duration of cover crop usage (i.e., number of years since cover cropping was initiated) and SOC enhancement. In their discussion, the authors suggest that, because the average cover crop duration among studies was 5.2 years, this means an average annual C accumulation rate of 1.11t/ha divided by 5.2 years = 0.22 t/ha/year.  I suggest that they have a very weak statistical basis for that assumption. (It critically underestimates the measured SOC in tests with only 1-2 years of cover cropping and overestimates in tests from cover crop 8-10 years in existence.)

Crystal-Ornelas et al (2021) published Soil organic carbon is affected by organic amendments, conservation tillage, and cover cropping in organic farming systems: A meta-review. The review included eight comparisons of with and without cover crops. The measurement was only of SOC concentrations, not soil organic carbon stocks, and the overall difference was not statistically significant. However, for three comparisons involving only the upper 15 cm of soil, cover crops meant a significant increase in SOC concentration. There was a reverse trend, though not statistically significant, for five studies with measurements down to 50 cm.

Chahal and Van Eerd (2018), in a paper entitled Evaluation of commercial soil health tests using a medium-term cover crop experiment in a humid, temperate climate, established identical adjacent experiments in two consecutive years at Ridgetown Ontario on sandy loam soil.  Each involves a rotation of several field and horticultural crops with four cover crop treatments and one with no cover crop. While this paper is not a multi-study review like the others, I’ve included it here because of its special relevance to Ontario agriculture where I live and farm. Inclusion also reflects appreciation for the enormous amount of work that this research has entailed.

The authors measured the soil organic carbon content and bulk density for the upper 15 cm of soil in all plots in early September of the sixth year after the initiation of each experiment. There was no effect on cover-crop treatment on soil bulk density. A significant increase in SOC in mg/g of soil with cover crops was measured in both tests, compared to the no-cover-crop controls. See the second column in the table below. (Values followed by the same latter within each test are not significantly different at P = 0.05.)

Using these data and the measured bulk densities of 1.62 (Test A, sampled 2015) and 1.66 (Test B, sampled 2016), I have calculated the equivalent quantities in t/ha of SOC for the upper 15 cm of soil; see values in column 3 of the table. The authors published equivalent numbers (t/ha of SOC), using the same base data in a 2020 paper. These are shown in the fourth column in the table. The values I’ve listed were extracted from a bar graph in the 2020 paper using the software program, Greenshot. I am not clear as to why the values differ between the two papers for Test B but not Test A.

Notwithstanding the above, the data show a consistent cover crop effect on SOC enhancement, relative to no cover crop plots, in both trials and both papers. That’s consistent also with the length of time cover crops grew after short-season horticultural crops were harvested in this study.

Table: Data on soil organic carbon for two cover experiments at Ridgetown Ontario, from Chahal el al papers (2018, 2019 and 2020)

TreatmentSOC, mg/g, 2018 paperSOC t/ha, 2018 paperSOC, t/ha, 2020 paperSOC, mg/g,2019 paper
Test A, planted 2007, measured September 2015
No cover33.8c82.182.1c27.7ab
OSR + Rye37.2a90.491.1a30.9a
Test B, planted 2008, measured September 2016
No cover34.0b84.763.6c28.2b
OSR + Rye36ab89.682.0a28.7ab

However, I have two reasons to be uncertain about the results.

The first is that the quantities shown in columns 2-4 are well above the 3.8% soil organic matter concentration that the authors measured at the beginning of the studies. The quantity 3.8% soil organic matter (SOM) is equivalent to about 22 mg/g SOC assuming SOM is 57% carbon. Twenty-two mg/g SOC equates to about 50-55 t/ha of soil C assuming a bulk density of about 1.6 and soil depth of 15 cm.

The second reason involves a second set of SOM data which the authors obtained from the sample soil samples collected at the same times in September 2015 and 2016. These were sent for analysis at an analytical service lab at Cornell University, with the results published by Chahal et al (2019), and also shown in the fifth column in the table above. These quantities are more similar to the SOC concentration measured when Test A was started. They do show a trend for higher SOC compared to no cover crop with cover crop treatments containing cereal rye. However, the amount of SOC enhancement measured is less than in the 2018 and 2020 papers.

I must emphasize that my comments about divergent data in no way detract from the high regard I have for Dr. Van Eerd and her research team, and their extensive research on soil quality. Even with the uncertainties I’ve raised, the research results indicate that higher SOC did occur some cover crop treatments.

I also want to acknowledge that Dr. Van Eerd was the one who alerted me to the reality that higher SOC values in cover crop treatments do not necessarily mean net carbon sequestration. It can equally means less loss in SOC with use of cover crops compared to no cover crops.

Bottom Line: What’s the overall conclusion?

A very substantial amount of research effort has gone into assessing the effect of cover crop usage on soil organic carbon, with apparent strengths and weaknesses in all of the studies. None of the reviews considered research reports other than those written in English – with the exception of Jian et al which also included reports in Chinese. Given that cover crops are of much interest to applied agriculturalists in non-English speaking countries – and notably Europe – the inclusion of reports in other languages in the meta-reviews would have been useful.

Despite the above, it does seem clear that use of cover crops commonly means more soil organic carbon relative to no cover crops. This is especially so when the growing season is long with average annual temperature relatively high and when the cover crops are grown for a long duration. The latter is more likely when the main cash crop matures very quickly (example, for some horticultural crops) or when the cover crop is in place for most or all of the full growing season (eg., between rows of perennial crops like grapes or as a full-season green manure crop). This also applies for a common practice in temperate winter-wheat growing regions like Ontario where red clover is ‘frost-seeded’ into wheat stands in early spring and allowed to grow until terminated in late autumn.

Conversely, the chance for significant, measurable increases in soil organic carbon seems much less likely when the cover crop is planted after harvest of a full-season, or near-full-season, primary crop and killed later that autumn or before spring planting the following year – and in climates where no crop growth occurs for many months of winter.

Published research also shows that soil organic carbon enhancement is more likely to occur on soils with higher clay contents than those high in sand.

The analysis by McClelland et al showed a distinct difference in relative SOC accumulation for tests/plots accumulating more than 7 t/ha/year of above-ground cover crop biomass versus those accumulating 7 or less. As a starting point, 7t/ha/year might be a useful yardstick for judging whether a detectable cover crop effect on soil organic carbon is to be expected for a given site, or not.

I note that McClelland et al found an even closer statistical fit between length of time from planting to termination and SOC level, but this is difficult to apply where the time from planting to termination may include many months of no growth (eg., winter in most of Canada).

I suggest that none of the studies reviewed above gives a reliable estimate of the rate of annual SOC improvement that might be achieved at any given location with cover crop usage. The limitations in published data include:

  1. Reports based very few years of cover cropping (sometimes only one).
  2. The inclusion of data from experiments where the ‘cover crop’ was the only crop grown for an entire season – and, hence, not really a cover crop by the definition stated above.
  3. The inclusion of experiments measuring SOC or soil organic matter percentages only, with no data provided on soil bulk densities, especially for the cover-crop treatments. Procedures have been developed for estimating the missing bulk-density values, but these introduce sizable errors.
  4. Different sampling depths within or among experiments – range from 2.5 cm to more than 100 cm (though few below 30 cm) – often with simple calculations used to ‘standardize’ to a common depth.

In addition, none of the research reviewed included situations where cover crops were used for late-season grazing by ruminant animals.