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.

Methane

• 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 TerryDaynard@gmail.com if you spot errors – typographical and other – in this posting. Thanks.