GHGMP Feature Articles
Reduced tillage helps reduce carbon dioxide levels
Low tillage systems are being entrenched on Canadian farms
Canadian farmers who have adopted conservation farming practices such as zero tillage and direct seeding over the past 20 years are contributing to Canada's overall objectives of reducing Greenhouse Gas (GHG) emissions.
The techniques, which eliminate or reduce tillage in crop production play a dual role in capturing and storing carbon in the soil. First, plants such as grain, oilseeds, corn and forage crops take carbon dioxide from the atmosphere through photosynthesis and store it in plant structures.
Second, the absence of tillage slows the breakdown of plant material both on the soil surface and in the root zone, therefore slowing the release of carbon back into the atmosphere. The carbon taken from the atmosphere is stored in the soil.
Carbon sequestration is an important process in reducing GHG emissions, say soil scientists and soil conservation specialists. Through chemical conversion, one tonne of soil carbon can produce 3.67 tonnes of carbon dioxide. The more carbon stored, the less carbon dioxide being released.
Research on Canadian climate change estimate Canadian cropland can store or sequester as much as 22 million tonnes of atmospheric carbon dioxide per year by using best management practices such as zero tillage. It's further estimated that grazing land can store another three million tonnes of carbon dioxide through improved grass production and proper grazing management.
Zero till and direct seeding production practices, along with reduced use of summer fallow, can store from 0.3 to 0.5 tonnes of carbon per hectare per year to the soil depending on the weather and moisture patterns.
"In short, practices that increases carbon storage are usually good," says Dr. Henry Janzen, a research scientist specializing in soil biochemistry with Agriculture and Agri-Food Canada's Lethbridge Research Centre. "They are good for the environment and good for producers."
The main benefit of sequestering carbon, says Janzen, is to improve soil quality and productivity. The amount of soil carbon is directly related to soil organic matter, which affects the soil's quality, tilth, ability to resist erosion and nutrient supplying characteristics.
"We've been looking at building soil organic matter for many decades and we've done it for many important reasons other than reducing atmospheric carbon dioxide," says Janzen. "We do it for reasons of productivity, conserving soils and ensuring soils are productive for generations to come. And if we can reduce atmospheric carbon dioxide at the same time, so much the better."
Approaches to zero tillage and conservation farming need to be modified for different regions of the country. The benefits of using a zero till drill to seed directly into standing wheat and barley stubble has been demonstrated across much of Western Canada. However, new approaches are being evaluated through Ontario, Quebec and Atlantic Canada, which produce different crops, with different cropping techniques under higher moisture weather regimes.
Adoption of zero till farming practices varies by region and crop. In Ontario it's estimated about 10 percent of corn, about 50 percent of soybeans and about 75 percent of wheat are produced under no-till, while in Quebec it's estimated 20 to 25 percent of soybean and grains are no till. Figures are higher if reduced tillage production is included.
Zero till has generated limited interest among corn growers in Eastern Canada.
Slower adoption of zero till is due in part to some earlier demonstrations which showed negative results. In New Brunswick, for example, zero till corn projects showed growers can reduce equipment and field operating costs, but at the expense of reduced yields, says Pat Toner, a soil management specialist with New Brunswick Department of Agriculture, Fisheries and Aquaculture. That's mostly blamed on the crop residue keeping the soil cool in spring, which may slow the growth of the heat-loving crop. A renewed effort is being made to demonstrate the value of zero and reduced tillage to Atlantic Canada farmers using new techniques such as zone or strip tillage.
As well, maintaining ground cover is also important to reducing water erosion," says Susannah Banks, field co-ordinator for New Brunswick of the federally funded Greenhouse Gas Mitigation Program (GHGMP).
However, in areas were potatoes are a main crop, for example, little crop residue remains after harvest. Techniques such as seeding winter wheat or other cover crop after potatoes to prevent soil erosion during early spring runoff and after major rainfall events, may be a more viable option.
"We have to find ways to demonstrate to producers in Atlantic Canada the value of zero and reduced tillage and maintaining ground cover," says Jerome Damboise, Project Co-ordinator for the Eastern region of the GHGMP who works out of the Eastern Canada Soil and Water Conservation Centre.
Prairie producers adopt technique
Depending on the region and weather patterns Western Canadian producers have been buying into conservation farming practices for more than two decades. In Manitoba, where zero tillage was pioneered about 25 years ago, the practice has been adopted in the drier parts of the province. Of about 12 million cropped acres, about two million are cropped under zero till systems.
In Saskatchewan, about 50 percent of the seeded acres, or 16 million acres, are farmed under zero till. While in Alberta about 27 percent or 7 million acres are cropped under zero till practices. British Columbia reflects both trends in the country with producers in the Peace River region adopting similar conservation farming practices as the Prairies, while farmers in the Lower Mainland face similar challenges as producers in Eastern Canada.
Research proves the point
The value of zero till and direct seeding in increasing stored soil carbon has been documented through research. A three-year study by the Prairie Soil Carbon Balance Project confirmed "direct seeded crops take more carbon dioxide out of the atmosphere and have more carbon to store," than conventionally tilled crop land. Researchers also observed a slight increase in crop yields.
Recognizing differences in moisture patterns across the Prairies, the project found direct seeding in the drier open prairie captured about one-third of a tonne of carbon per acre per year in the top 12 inches of soil, while in the more moist parkland areas nearly two-thirds tonne per acre of carbon was stored.
Carbon flow similar to a lake
Carbon storage is a dynamic process, says Janzen. "Organic matter is continually being added to and lost from the soil. It's really a flow we're talking about...like a lake with water coming in and going out. And it is the difference - the body of the lake - that amounts to the storage." The lake level or amount of carbon storage can be influenced by either increasing the "inflow" or by decreasing the "outflow."
Prairie soils lost much of the organic matter from the surface layer, soon after they were first broken, says Janzen, estimating between 20 and 30 percent or soil organic matter has been lost. "Part of that can be recovered with improved management practices," he says. "Within a few decades, carbon storage will again reach a plateau or a point of stability."
Adopting conservation tillage or other practices that preserve organic matter is an important part of a sustainable agriculture system, he says. "Carbon sequestering is only one part of the whole process. The main objective is to enhance the resilience and productivity of our farm land."