Carbon Sequestration and Direct Seeding

Brian McConkey*, B. Chang Liang*, Glenn Padbury**, and Wayne Lindwall*

Semiarid Prairie Agricultural Research Centre, Agriculture and Agri-Food Canada

*Swift Current and **Saskatoon.

What is carbon sequestration?

Carbon sequestration refers to taking carbon dioxide (CO₂) out of the atmosphere through crops and storing that carbon in soil organic matter. Since first broken for crop production 80 to 120 years ago, prairie soils have lost about one-third of their native soil organic matter. This soil organic matter was lost because: 1) the tillage exposed the native soil organic matter to more decomposition, 2) the annual crops returned less residue than the native prairie (in particular, summerfallow added no residue except weeds), and 3) moister soil accelerated decomposition since annual crops did not keep the soil as dry as the native grass did. While the soil organic matter was being lost, the carbon in that soil organic matter was being lost to the atmosphere as CO₂. Each tonne of carbon lost from soil organic matter released 3.667 tonnes of CO₂. Similarly, each tonne of soil organic carbon increase removes 3.667 tonnes of CO₂ from the atmosphere. The process of carbon sequestration is often referred to as making the soil a sink for CO₂.

Presently, we estimate that the soil organic matter on cropped prairie soils is stable and at an approximate steady state where annual additions of carbon from crop residues roughly equal the amount of carbon released as CO₂ by soil microbes each year. If we change agricultural management in ways that increases soil organic matter, such as adopting direct seeding, CO₂ is removed from the atmosphere and sequestered as soil organic matter. Hence, carbon sequestration is essentially recapturing carbon from the atmosphere that had been emitted from the soil in the past (see Figure 1). Carbon sequestration does not continue indefinitely as eventually a new steady state is reached when residue inputs equal total decomposition of soil organic matter. The length of time before a new steady state soil organic carbon level is reached is uncertain but most sequestration occurs over the first 10 to 20 years after the adoption of the new management practice.

Figure 1. Change in soil organic carbon from breaking of native grass, attainment of new steady state, and then adoption of carbon sequestering practice (hypothetical example).

Why should I care about carbon sequestration?

CO₂ is a greenhouse gas. This means that CO₂ absorbs radiation that otherwise would be radiated to space. Instead the greenhouse gases are re-radiated back to the earth, causing warming of the earth's surface. The world's rising consumption of fossil fuels (coal, petroleum, and natural gas) is greatly raising the atmospheric CO₂ concentration. The concentration of greenhouse gases in the atmosphere, primarily CO₂, are at their highest concentrations in the last 100 000 years and are still increasing rapidly.

One possible consequence of the buildup of greenhouse gases is that there will be dangerous climate change where the climate changes faster than we can adapt and/or the climate becomes unstable such that we can not cope with the increased frequency of extreme weather. These potential climate problems are obviously critical for agriculture. As insurance against such climate change, the world's most industrialized countries have signed the Framework Convention on Climate Change (FCCC) that requires these countries to reduce sources and enhance sinks of greenhouse gases. In the 1997 Kyoto Protocol to the FCCC, Canada agreed to reduce its greenhouse gas emissions to 6% below 1990 emissions during the 2008-2112 periods. This would equal about 20 to 25% reductions below projected national emissions if current emission trends continue. Because of the Kyoto Protocol, otherwise profitable emitters of greenhouse gases want to use carbon sequestered in farmland to offset some of their greenhouse gas emissions. The consequences of Canada failing to reach or make real progress against our greenhouse gas reduction targets depend on what happens in other countries. If other countries make much more progress than Canada, those countries would almost certainly use that advantage to try to steal economic activity from Canada, probably through trade penalties against Canada. Prairie farmers, being highly dependent on exports, would be especially vulnerable in such a scenario. Regardless of whether industrialized countries achieve their planned reductions under the Kyoto Protocol, there is little question that if climate change continues, Canadians and/or our major trading partners will insist we move to a economy with less greenhouse gas emissions. Greenhouse gas budgets could easily be as important to farm businesses in the 21^st century as dollar budgets were in the last century.

How much carbon is sequestered with direct seeding?

Table 1 shows the gains that can be expected in the first 15 years after adoption of direct seeding. The heavier the soil the better it is able to store or sequester carbon. Carbon sequestration varies with soil zone because the lower the initial soil organic matter concentration in the soil or the greater the crop production, the greater the sequestration expected.

Table 1. Expected gains in carbon sequestration for adoption of direct seeding and reduced fallow for the prairies.

Taking advantage of the water conservation benefits of direct seeding, many growers reduce the frequency of fallow when they adopt direct seeding. Table 1 also shows the gains expected for converting from crop-fallow to continuous cropping. For other changes in fallow frequency, we suggest using the following equation:

Cgain = 2 x Cgain_Table1 x (FallowFreq_old - FallowFreq_new) Eq (1)

For example if a farmer converts from fallow once every three years (FallowFreq_old = 1/3 = 0.33) to fallow once every five years (FallowFreq_new = 1/5 = 0.2) in the Thick Black soil zone, the estimated gain from Eq (1) is:

Cgain = 2 x 0.6 x (0.33 - 0.2)= 0.156 t carbon/ha/yr

How do multiple carbon sequestering practices affect soil carbon gains?

Based on our measurements, the effects of several carbon sequestering practices appears to be approximately additive (see Figure 3). If many new carbon-sequestering practices are adopted continually, carbon gains can increase both faster and for longer period than shown in either Figure 1 or 2.

Figure 2. Hypothetical change in soil organic carbon with adoption of one sequestration practice, attainment of a new steady state, and then adoption of another carbon sequestering practice.

In cooperation with SSCA, we measured differences between paired fields - one being conventional managed and the other being under direct seeding. These comparisons generally involve both reduced fallow frequency as well as a change in tillage system. Table 2 summarizes some of the results from these comparisons. In these sort of comparisons, it is unreasonable to expect that the fields had the same amount of organic carbon when the one field was converted to direct seeding so precise assessment of carbon gain due to the change to improved land management is not possible. Nevertheless, the results clearly show that Saskatchewan farmers are sequestering carbon.

Table 2. Examples of soil carbon gains accomplished by Saskatchewan farmers.

What exactly is soil organic matter and is carbon sequestration permanent?

Soil organic matter is a catchall term to describe organic residues from plants and soil microbes in various states of decomposition. Once residues from above- and below-ground portions of the plant are added to the soil, soil microbes immediately start decomposing those residues. Over time and through transformations by many types of soil microbes, chemical combinations of well-decomposed organic materials are produced that are quite resistant to further degradation. These resistant organic materials, often called humus, represent the majority of soil organic matter in prairie soils. We know that the average age of the humus is more than a thousand of years old. Humus plays an important role in the providing the soil with a good structure necessary for good pant growth and water infiltration. However, because it is not readily acted on by soil microbes, humus does not play a large role in nutrient cycling. The less decomposed organic materials from soil microbes and plant residues represents 20-50% of soil organic matter. This portion of the soil organic matter is a major source of plant nutrients such as nitrogen, phosphorus, and sulfur. These nutrients are released as byproducts of decomposition because the microbes are using the carbon for energy and releasing it as CO₂. The N, P, and S in the soil organic matter that is surplus to the needs of the microbes is left as "waste" products that plants then take up. After the adoption of an improved soil management practice like direct seeding, most of the increase in soil organic matter is these more active portions of the soil organic matter that can be still be decomposed. For this reason, if conventional tillage adopted again after the conversion to direct seeding, the newly sequestered carbon is readily lost (see Figure 3). Since most of the carbon from the plants is added to the surface, almost all the changes in carbon sequestration occur in the upper 10 to 20 cm of soil.

Figure 3. Hypothetical example showing that carbon sequestration is a reversible.

Would anyone really buy my sequestered carbon and for how much?

In October 1999, GEMCo (a consortium of Canadian utilities and energy companies) purchased 2.8 million tonnes of greenhouse gas reduction in CO₂ equivalents from Iowa farmers. Although the exact details are confidential, it is useful to look at the basic features of this deal because it could be the blueprint for other such deals with farmers. The Iowa deal is based on the purchase of CERCs (Certified Emission Reduction Credit) from IGF Insurance, a major crop insurance firm in Iowa. The Iowa farmers chose to have IGF act as the organization to pool and sell the CERCs of the participating farmers. Farmers create CERCs by 1) shifting from intensive to minimum or no-tillage methods, 2) adopting better crop rotation and/or soil conserving practices, 3) planting woodlots or other environmentally appropriate perennial vegetation on marginal land, 4) using waste biomass for products that store carbon for long period, 5) using animal wastes to reduce nitrogen fertilizer use, 6) burning crop residue or sustainable managed wood waste to replace fossil fuel use on the farm, 7) installing appropriate digesters and other equipment to burn methane generated from animal waste, 8) utilizing waste biomass to produce ethanol Note that only activities 1 through 4 above involve carbon sequestration, the other four methods of creating CERCs reduce fossil fuel use (activities 6 and 8) , reduce N fertilizer use (activity 5), or reduce another greenhouse gas, methane (activity 7). There is an initial payment by GEMCo primarily to set up the mechanisms including training and technical support for farmers as they make changes to their farming operations to create CERCs. The value of the emission reductions is in the range of US$0.50 to $3.00 per tonne of CO₂ or about CDN$2.65 to $16.00 per tonne of carbon. For carbon sequestration via activities 1 and 2 above, there is a base payment for 0.2 t C/ha/yr. If the farmers can verify larger carbon sequestration through verification systems like the Prairie Soil Carbon Balance Project, they can then offer those extra CERCs for sale. GEMCo has first right of refusal on additional CERCs above the initial 2.8 million tonnes. From the sale of the CERCs also comes IGF's costs associated with the project set-up including supplying technical support to the farmers. For carbon sequestration due to reduced tillage, the farmers can only claim a CERC after having been using reduced tillage for at least 6 years. After having being paid for the CERC, the farmer has no obligation to continue any particular practice. Thus, the CERC only covers reductions for a specified time not a permanent reduction (if the farmer reverted to intense tillage the resulting extra CO₂ emissions would, presumably, have to be offset somewhere else in the economy). Since the payment is for the practice, the payment goes to the land manager not the landowner unless the payment is partitioned in a separate agreement between landowner and lessee.

In summary, future deals of this type in North America may share the same basic features including: a single organization pooling sequestered carbon from many farmers, payments for farm practices not carbon itself, inclusion of several farm practices that reduce net emissions of greenhouse gases, and reasonable flexibility for the participating farmers.

The appropriate value for sequestered carbon for such deals between offset purchasers and offset-producing farmers is uncertain. An important feature of carbon sequestration on cropland is that it can be accomplished almost immediately compared with the some time to make major technological changes to fossil-fuel burning industrial or transportation equipment. This could mean that the value of offsets could be greatest in the near future and decline with time as new technology becomes available that reduce emissions. For example, if the government imposed a carbon tax of CDN$0.10 per litre of gasoline tomorrow to immediately induce consumers to reduce fossil fuel use, this is the equivalent of CDN$44 per tonne of CO₂ ($162 per tonne of carbon) or at least 10 times the value of sequestered carbon in the GEMOo-Iowa farmer deal. However, if climate change becomes important enough and other technological fixes are not reducing emissions fast enough, the value of sequestered carbon could be even higher in the future than now.

Doesn't carbon sequestration just let major greenhouse gas emitters off the hook?

Canada and the U.S. are strong supporters of emissions trading. Under this system, a market is established for net emission reductions so that those enterprises that can most cheaply reduce greenhouse gas remissions should do so and offer emission reductions for sale to those enterprises that can not make reductions as cheaply. The value of offsets or reductions is set by the market at a level so that the national economy accomplishes its total net emission reduction target at lowest possible cost. If each emitter is forced to meet a prescribed emission reduction target, then, for many industries, the cost of meeting emission reductions is large and they would be forced to pass these large costs onto their customers -- including farmers. So the consequence of forcing each greenhouse gas emitter to accomplish prescribed reductions in their own operations without the option of buying sequestered carbon offsets could very well be increased input costs and reduced income for farmers.

Won't prairie agriculture need carbon sequestration from direct seeding to offset its own emissions?

Canadian agriculture itself is a major emitter of greenhouse gases (about 10% of Canada's total emissions) and those emissions are expected to increases substantially in the next decade on the prairies if some of the projected increases in livestock production occur. Therefore, for prairie agriculture to be compliant with Kyoto reduction targets, it could well need all the carbon sequestration to offset its own emission increases. In the market-based offset trading system outlined above, emitters in the agricultural sector who need offsets to their own emissions would purchase those offsets from whomever is the least expensive supplier at that time. Under that system, farmers would be free to decide if, for how much, and to whom they wanted to sell any offsets.

The Kyoto Protocol only applies to the 2008-2012 period so how will be carbon sequestered from 1990 to 2008 be valued for greenhouse gas offset credits?

Although there is growing international support for allowing carbon sequestered on agricultural land, this emission offset is not included in the Kyoto Protocol. So there is no assurance that any carbon sequestration will have any value. Canada has been on the forefront of these international negotiations and the Prairie Soil Carbon Balance Project with SSCA has been instrumental is building that support by showing that there are ways to quantify and verify soil carbon changes. There is little likelihood that carbon sequestered between 1990 and 2008 would ever be accepted as a valid offset by the international community. However, the Canadian government could implement a credit for early action policy to reward those who have either reduced sources or enhanced sinks since 1990. Although these early-action credits would not contribute to Canada 's Kyoto commitments directly, they are valuable for moving the economy to a more greenhouse-gas friendly position by the 2008-2012 period. The GEMCo deal to buy sequestered carbon in Iowa is based on the assumption by GEMCo that there will be credit for early action in the U.S. that then gives monetary value to any sequestered carbon before 2008.

Should I mismanage my land to reduce soil organic carbon by 2008 so I can then adopt sequestering practices and get paid for carbon increases from 2008 to 2012?

Environmentalists and governments are well aware that such behavior to increase CO₂ emissions from the soil now to capture carbon sequestration later is a possible consequence of the Kyoto Protocol during the period up to 2008. If prairie farmers change their management on a broad scale to deplete soil organic matter solely to be able to capitalize on future carbon sequestration credits, that, in itself, would surely convince the international community not to accept carbon sequestration on agricultural land as a valid emission offset. A well-designed national credit for early action program would prevent such problems in the first place and reward farmers now for being good land managers.

What is the Prairie Soil Carbon Balance project?

In 1996, SSCA, GEMCo, and Agriculture and Agri-Food Canada started the Prairie Soil Carbon Balance Project (PSCB). The first part of the PSCB was to quantify and verify the changes in carbon sequestered from the adoption of direct seeding and any associated reductions in fallow. This component of the PSCB is also called the Saskatchewan Soil Enhancement Project. After this part of the PSCB was already ongoing, another more research-oriented project into carbon sequestration on native and tame forages was initiated.

The direct seeding component of the PSCB involves precise soil carbon benchmark or verification sites on 150 farm fields seeding across Saskatchewan. These fields were being converted to direct seeding in 1997 and the soil organic carbon at the benchmark was determined in fall 1996 (a few before spring seeding in 1997) and again in fall 1999. Thus, the change in soil carbon over those three years (1997-1999) will be accurately determined. The benchmarks themselves are invisible to the farmer-cooperator. In 23 of the fields, the farmer-cooperators also maintained a strip of a few acres in conventional tillage management. In these fields, then, we also know how soil carbon changed under conventional tillage (in a three year period a different weather pattern from the past alone can cause changes in soil organic carbon). In practice, the changes in carbon sequestration for all of Saskatchewan will be estimated by a sophisticated computer model of soil carbon. The benchmarked fields will be used to verify that these estimates are accurate over a wide variety of soil and weather conditions.

What about direct seeding and other greenhouse gases?

For agriculture, the major greenhouse gases are CO₂, nitrous oxide (N₂O), and methane (CH₄). CH₄ emissions are largely from cattle directly and some from livestock manure. N₂O emission comes from animal manure but there are also important emissions from cropland. N₂O is emitted from cropland during nitrification (conversion of ammonia to nitrate) and, especially in wet soils, during denitrification (conversion of nitrate to N₂O and nitrogen gas).

Undoubtedly, there will be increasing pressure and possible payment for using good fertilizing practices such as fertilizer banding that is already a typical practice among direct seeders. Reducing fallow is also important since fallow usually leaves the soil both higher in nitrates and soil water than stubble so fallow favours denitrification. To illustrate how carbon sequestration and N₂O will be linked in the future, the Iowa farmers who want to claim carbon sequestration offset credits for fields where they have adopted reduced tillage must keep and supply detailed records of nitrogen application and budgets for those fields.