Over the past decade, SSCA has promoted the concept of using direct seeding to create soil carbon sinks as a way to offset greenhouse gas (GHG) emissions. In addition to carbon sinks, a variety of practices are being developed to further lower agricultural emissions. In the future, SSCA will become more involved in helping producers not to adopt practices that store carbon but also help them reduce their GHG emissions.
Unlike other economic sectors, greenhouse gas emissions from agriculture are not from burning fossil fuels. The major emissions in agriculture are Nitrous oxide (N2O) and Methane (CH4). While N2O and CH4 emissions are small compared to CO2, these gases are a concern because they are much more potent greenhouse gases. The greenhouse warming potential (GWP) of N2O is 310 times that of CO2 while CH4 is 21 times that of CO2. N2O emissions are closely associated with nitrogen applications from both fertilizer and manure.
Nitrous oxide is formed as a part of the nitrogen transformation processes in the soil, namely nitrification and denitrification. The rate of N2O emitted to the environment is highly sensitive to conditions in the soil and farming practices. Management practices that minimize nitrogen build-ups and discourage waterlogged conditions that favour denitrification. In many settings, the practices listed below can help reduce N2O emissions and improve the N fertilizer efficiency.
Optimizing nitrogen application rates to match crop use is the most effective way to minimize N2O emissions. While not perfect, soil testing is the best method to determine the target nitrogen rate. Split fertilizer applications, based on late spring growing conditions, allow producers to fine tune their application rates. Variable-rate fertilizer applications also have the potential to better match the amount applied to the crop's needs.
As a source of available nitrogen, manure is also a major source of N2O emissions. As with fertilizer-N, the best way to minimize emissions is by matching the application rate to crop use, avoiding over-applications.
Timing is as important as the rate of application. The amount of N2O released is related not to the amount of N applied, but to the amount of N unused by the crop. Applying just prior to the time of maximum uptake by the crop or using split applications reduces the amount of time N is in the soil before crop uptake. The simplest management change to improve nitrogen timing is to apply fertilizer or manure in spring rather than fall.
Recent research in western Canada has shown that N2O emissions are lower in direct seeding systems than under conventional tillage. Optimizing nitrogen applications in a direct seeding system is probably the most effect overall strategy to minimize N2O emissions.
While still experimental, certain chemicals, called nitrification inhibitors, applied with fertilizer or manure, suppress the conversion of ammonia to nitrate potentially reducing N2O emissions.
Methane, also known as natural gas, emissions in agriculture are primarily associated with livestock. The highest percentage of CH4 generated by Canadian agriculture comes from ruminant animals (i.e. cattle, sheep, goats). These animals have a fore-stomach (rumen) where microbial fermentation partially digests feed material in the absence of oxygen. Five to 10 percent of the Carbon in the feed is released at this point as CH4. Practices that improve feed conversion in cattle also reduce CH4 emissions
Methane is also emitted from manure. The amount emitted is greatly impacted by methods of storage. When manure decomposes in the presence of oxygen, CO2 is released. If manure is stockpiled, inadequate aeration within the pile may lead to CH4 production. As well, higher amounts may be released from stored liquid manure because of limited aeration. Once manure is applied to the land, adequate exposure to the air means little additional CH4 is produced. Emission from manure accounts for about 20% of the total CH4 emitted by livestock. Pig manure plays an important role here because of the large number of animals in Canada and because of how the manure is stored. Managing emissions from manure takes two main approaches: either reducing anaerobic decomposition through improved aeration or directly capturing the CH4 to use as an energy source.
More information on managing greenhouse gas emissions in agriculture is available through the Soil Conservation Council of Canada's website at www.soilcc.ca.