Prairie Soil Carbon Balance Project

Garry Mayerle, P Ag

Conservation Agrologist

Saskatchewan Soil Conservation Association

The Prairie Soil Carbon Balance Project was initiated to provide scientific verification that Saskatchewan farmers who have adopted direct seeding are storing carbon (C) in their soil. After 3 years the project has shown conclusively that direct seeding does build soil C and therefore can significantly reduce greenhouse gases.

There has been enough information about Western Canadian research projects and anecdotal evidence spread around that most producers believe that soil organic matter increases when producers use conservation farming practices such as direct seeding. Soil carbon is directly related to soil organic matter. Soil organic matter is the stuff that gives our soil its: colour, quality, tilth, ability to resist erosion, and nutrient supplying characteristics. An important conversion to remember to understand this relationship is that soil organic matter is 58% carbon. Once this relationship is understood it is easy to follow the progression from building this organic matter to increasing soil carbon. Scientifically acceptable results are important as we seek to get international powers to accept our soils as a recognized sink in the greenhouse gas issue.

The most prolific greenhouse gas is carbon dioxide (CO₂). A simple "chemical conversion" that shows this progression is that 1 tonne of C can produce 3.67 tonnes of CO₂. Greenhouse gases act like an insulating blanket trapping radiation being given off by the earth and increasing the average temperature of the planet by several degrees. This slight rise in average temperatures could have very detrimental effects on "life" as we know it, and especially on agricultural production. Plants take CO₂ out of the atmosphere and break it down into carbon and oxygen through the process of photosynthesis. The carbon is built into plant structures. In our annual cropping system much of this plant structure is returned to the soil every year. Conservation practices such as direct seeding maintain more of this carbon in our soil than traditional production systems. The net effect is that carbon has effectively been taken out of the atmosphere and stored or sunk into our soils. The decision of international policy makers to accept soils as an acceptable sink for CO₂ could have far reaching effects on our agriculture. Prairie soils have the potential to sink significant quantities of CO₂. Best management practices such as direct seeding create a sink that will be filled in time. The advantage is that this "time" will give greenhouse gas emitters the opportunity to develop cheaper ways to reduce emissions.

The Prairie Soil Carbon Balance Project involved 4 different levels of trials. See Table 1 for a summary. The first level was evaluating the changes in soil carbon content as fields were converted to direct seeding. The goal was to establish enough sites to give good statistical data from every combination of soil type, texture, and regional climate in the agricultural area of the province. A second level of trials was designed similarly but also included a 2 to 10 acre strip of tilled field for comparison. The purpose was to reduce other variables that go along with low disturbance seeding. The third level was carbon measurements at different landscape positions on fields that had recently been converted to direct seeding. The 4^th level of trials compared carbon stored in land that had already been directed seeded for a number of years to across-the-fence-line conventionally farmed land. Another component of the project established later evaluated carbon storage on native and tame forages.

Table 1. Summary of project levels.

There are a number of people that collaborated to make this project happen. One of these groups, a very important and diverse group, was the 150 cooperating farmers who had fields that fit the criteria for establishing carbon monitoring sites. These producers were ready to volunteer their fields and the SSCA is extremely grateful to them. This next group is the Saskatchewan Soil Conservation Association (SSCA). The SSCA is a farmer directed organization that promotes production systems that improve the land for future generations. They solicit funds from public and private organizations and sell memberships to accomplish this goal. One of the key means of carrying on activities to accomplish their mission is to hire professional staff to promote soil conservation and particularly increase the uptake of direct seeding. SSCA staff found the required producer cooperators and collected cropping histories and background information to collaborate the carbon measurements. They also collected annual biomass samples at the level 2 sites. Agriculture and Agri-Food Canada and University of Saskatchewan research scientists and technicians carried out the more technical side of the project. Dr. Brian McConkey of Swift Current Research Station headed up a great deal of this section of the project. They did the research, soil testing, biomass determinations, and data manipulation. GEMCo provided the part of the funding that got the project going. GEMCo is a consortium of Canadian energy producing companies. Energy production typically burns a lot of fossil fuels releasing enormous amounts of CO₂.

SSCA was involved in 3 levels of the project. In the first 2 levels 137 sites were established. The level 1 & 2 fields were chosen because they were being converted to direct seeding at the point that the project was starting. The purpose of each level 1 site was to be a benchmark sampling site. 3² soil cores were taken to a 16² depth and divided into 4² segments, which were analyzed to determine carbon content. Each site was called a micro site. The actual changes in soil carbon in each 4² x3² core would be very small. Think about a ½ tonne of C added to 26 tonnes already in the soil spread out over 43,560 cu.ft and the difference in C content in 6 3² soil cores looks pretty small.

The coring procedure was set up to eliminate as much as possible variables other than the effects of direct seeding that might change soil carbon content. The sites were 2m x 5m in size and were located in a level spot to minimize any effects of erosion. 6 soil cores were taken each time a coring was done. The initial cores were

The purpose of the level 2 trials was to track and recognize soil carbon changes that come along with production changes associated with direct seeding such as reduced fallow, increased use of fertilizer, or rotation adaptations. The only difference in the small tilled treatment in the level 2 sites was tillage operations that were supposed to represent the local equivalent of tillage in a conventional farming scenario. For the small compensation that these producers were receiving most of these sites would have had some type of tillage disturbance every year but probably not quite equivalent to a conventional production system in the area. There were 22 of these sites in the province. There was more in depth analysis on these sites. 3 micro sites were established in each of the tilled and directed seeded treatments with approximately 40 plus meters between them. Within a week of swathing stage square meter yield samples were taken at each of these sites for the 3 crops grown between the first and second soil coring. 3 samples were taken about 5 meters away from each microsite. The samples were dried weighed and threshed. Both yield and biomass comparisons could then be made between the tilled and direct seeded sites.

The 4th level of trials was completed near the beginning of the project. There were 9 paired farm comparisons in this level of the project. SSCA was involved in lining up these cooperators. Dr. McConkey reported on these comparisons at the last annual conference (see Table 2).

The natural processes of soil organic formation that store carbon in prairie soil depend on many factors. It is a slow process and the ability to measure any statistically significant change in less than 5 years was doubted at the outset of the project. However, soil C dynamics are quite well understood and soil scientists have developed several computer simulation models that can quite successfully predict soil C in a variety of situations. Predicting the effect of tillage systems on organic C is not as well developed. The change in soil C data from level 4 tillage comparisons and other research sites were used to develop parameters and thoroughly test the

Table 2. Examples of soil carbon gains in level 3 comparisons.

"Carbon Sequestration and Direct Seeding" by Brian McConkey, B. Chang Liang, Glenn Padbury, and Wayne Lindwall, Proceedings - Direct Seeding "Sustainable Farming In The New Millennium." p. 155-164.model.

One of the main problems with the level 4 site data was that no original C data was available. This model is also developed from combined data derived from databases of soils, landform, weather, and farm management. Integrating all this information with the use of a Geographic Information System (GIS) enables scientists to scale up the data to make predictions for large areas and even national estimates. The level 1 benchmark sites provide a check for the predictions the model comes up with and can also be used to refine the model.

Dr McConkey reports that the CENTURY model being used does need more refinement. The goal is to have a model in place that can predict with a great deal of confidence the amount of C that can be stored in specific situations. For wide area averages the model is relatively accurate but it is not good enough to use for a prediction for example for any particular quarter section where direct seeding has been established for say 5 years. One of the observations from this project was that we will not likely be testing each quarter section for the amount of C stored or sequestered. Soil C is just too variable even in a short area ½ mile x ½ mile. To accurately test soil carbon change in a quarter section one would need as many soil cores as were taken for this whole project and the cost would be prohibitive. McConkey adds that another 3 to 5 years of data from these sites should make it easier to more confidently predict soil C changes with the model.

Results

One of the significant results is the yield comparison on the level 2 trials (see Figure 3). Direct seeding increased total biomass production as compared to the tilled site production. A significant amount of this increase was in above ground residue. The importance of this in terms of stored C is that direct seeded crops take more CO₂ out of the atmosphere and so have more C to store. As far as yield goes the trend was to a slight increase in yield although the figure was not statistically significant. McConkey states, "On these fields the farmers had crop rotations involving a mix of grain legumes, oilseed, and cereal crops. Direct seeding provided a general productivity advantage to all these crops."¹

Gains in soil C may not be profitable for producers yet but the likelihood of a day when they will be rewarded for stored carbon seems imminent. The fact that industry money even funded this project points to its imminence. Further, the results from this project continue to make the case for the value of carbon stored in the soil stronger. On average across the province soil to a depth of 12² gained ½ tonne of C per ac during the first 3 years of direct seeding.

Regional differences in stored carbon were most obvious between the drier and the wetter areas of the province. The drier area can be characterized as semiarid. This is open prairie area where grasses predominated in the past. In these areas an average of 1/3 of a tonne of C /ac was stored in the top 12² of soil during 3 years of direct seeding. In comparison in the sub-humid area of the parkland where trees flourished in the past almost 2/3s of a tonne of C /ac was stored (see Table 3). The expectation is that as soil clay content increases more C should be stored. In this project soil texture did not play any clear role in the amount of soil C stored. It is important to remember that this data is just from the first three years of a new management practice.

One of the most significant results of the project is the demonstration of a method of confirming soil C changes with the introduction of new management practices that is not cost prohibitive. Setting up this quantification and verification project has strengthened support for including soil sinks on agricultural land as a method of reducing the concentration of CO₂ in the atmosphere.

Table 3. Average soil C change during first 3 years of direct seeding for all level 1 & 2 sites dividing province into wet and dry soil climatic zones.

References

1.) McConkey, B., Liang, B.C., Padbury, G., Ellert, B., Lindwall, W., 2000. Prairie Soil Carbon Balance Project A System for Quantifying and Verifying Change in Soil Carbon Stocks from Adoption of Direct Seeding and Better Crop Management.