Agriculture, Greenhouse Gases & the Kyoto Protocol

Environment
Agriculture, Greenhouse Gases & the Kyoto Protocol
by Don McCabe, Chair,
OCPA Research & Technology Committee

Part II
Because carbon dioxide (CO2) is the predominant greenhouse gas addressed under the Kyoto Protocol, methods to reduce CO2 emissions or remove CO2 from the atmosphere are being explored. As mentioned in Part I of this series (December issue), agriculture has unique opportunities in these areas.

Figure 1 shows the fate of soil carbon under agricultural management through time and its resultant effect on atmospheric CO2. Until they are cleared and worked, soils contain high levels of soil organic matter (soil carbon). With cultivation, the ‘mining’ of the soil of soil organic matter occurs to provide plant nutrients and simultaneously release CO2 from the breakdown of the soil organic matter.

GHG
Management Induced Changes in C of Agricultural Land

Eventually, a new equilibrium (or steady state) of soil organic matter is reached where whatever carbon inputs of roots, leaves, manure, etc., match the release of CO2 from soil organic matter oxidation (breakdown). This means that the atmospheric CO2 level is remaining constant.

With a management change to reduced tillage or no-till production, soils can start to replenish lost organic matter. That is, they can ‘sink’ CO2 back into the soil from the atmosphere via photosynthesis of plants and the subsequent conversion of the plant organic matter to soil organic matter.

Corn is one of the best plants for photosynthetic efficiency, as it can convert carbon dioxide to organic matter at a faster rate than most other plants. For scientists, this is known as the C4 photosynthetic pathway.

Coupling its photosynthetic efficiency with a long growing season explains why corn can produce such high yields of organic matter.

Table 1: Soil organic matter levels offer 18 years of various tillage systems on a silt loam soil.
Tillage System	Soil Organic Matter (tonnes/hectares)
Zero Tillage (No-Till)	86.2 a
Fall Chisel Plow	73.1 ab
Offset Disc	74.3 ab
Spring Moldboard Plow	74.8 ab
Fall Moldboard Plow	66.4 b
(Least significant difference (P=0.05) = 13.8) Source: Tony Vyn, University of Guelph, 1994.

During a growing season, one hectare of corn ‘absorbs’ (removes) 22 tonnes of CO2 from the atmosphere. One million hectares of Ontario corn will annually remove the equivalent of 9 billion litres of gasoline being burnt! (Approximately 35 billion litres of gasoline are consumed in Canada each year – about 1/3 of the total occurs in Ontario.) Comparing this 22 tonnes of removed CO2 to the estimate of 1.3 tonnes of CO2 released from growing a crop of corn (for fertilizer, fuel, pest control products, transportation inputs), shows corn is CO2 friendly with a ratio of 17:1 (CO2 absorbed to CO2 released).

Overall, agriculture has been an example for the rest of the country in reducing CO2 emissions - see Figure 2. If a constant level of CO2 emission of 7.3 mt ‘CO2 equivalents’ at 1990 levels is compared to the cuts in emissions that had been achieved through 1999, agriculture has cut out 37.2 mt CO2e from 1990 to 1999. This example is why ‘credit for early action’ is essential for agriculture.

For the individual farmer, CO2 emission reductions can be achieved through reduced field operations. At the same time that reduced tillage reduces emissions, soil sinks can also be filled with atmospheric carbon dioxide in the form of soil organic matter.

Few research studies comparing tillage operations for corn production and soil organic matter exist for Ontario conditions. This type of work requires long-term experimental plots because of the slowness of soil organic matter buildup. Tony Vyn did a comparison of tillage on a silt loam soil at the Elora Research Station of the University of Guelph. The results of this 18-year study are shown in Table 1. The soil organic matter levels with the same letter after them (a or b) indicate that the tillage system did not result in a statistically significant difference between the tillage systems in organic matter level. Therefore, 18 years of no-till corn production was the only tillage technique to significantly increase soil organic matter compared to conventional moldboard plowing in the silt loam soil.

Building up soil organic matter takes a long time; destroying it can happen very quickly. This reinforces the need for a ‘credit for early action’ principle for agriculture. Also, the soil sink carbon must be recognized as belonging to the landowner. The landowner has the responsibility of holding the soil carbon over time. Emission reductions from field operations belong to the producers. Therefore, if the landowner is also the producer, the credits go to the same person.

The credits are the connection to the Kyoto protocol. In summary, corn can provide a major uptake of CO2 from the atmosphere. A portion of it is sequestered into the soil by using no-till or reduced tillage options, combined with reductions in fuel usage. These opportunities will aid Canada in meeting its Kyoto Protocol requirements. However, producers will need assurance that they will receive proper recognition for their efforts. More research is needed to further substantiate the opportunities and overcome the challenges of no-till and reduced corn production.