| ||November 2000
Why are greenhouse gas emissions important?
Over the last century, modern industry and lifestyles have rapidly increased greenhouse gas (GHG) concentrations in the Earth's atmosphere. The majority of scientists studying this issue believe that these increasing concentrations are contributing to global warming. Rapid global warming could result in such problems as more severe weather events, more forest fires, and damage to water resources.
Canada has established a national target of an absolute 20% reduction in GHGs from 2006 levels by the year 2020, a reduction of 330 megatonnes from projected levels. The national and provincial processes to address Canada's commitment have indicated that all sectors of industry will be involved in reducing emissions. In addition, recent surveys show the majority of consumers in Canada and abroad believe action has to be taken now on GHG emissions.
The cropping industry also has an immediate economic stake in reducing its emissions because these emissions represent a loss of costly nutrients and other inputs. Following conservation practices that reduce emissions will also help producers meet other environmental objectives such as improved soil and water quality.
Emissions from Alberta's cropping industry
It is difficult to estimate GHG emissions from cropping practices because of differences in: soil moisture, soil temperature, land management practices (e.g. surface residue, tillage, nutrient management), cropping systems, geographic location (e.g. south vs. north, lower slope vs. upper slope) and soil properties. This makes it difficult to estimate total GHG emissions for the sector.
Photo courtesy of Ducks Unlimited Camrose, Alberta
The main gases emitted by the cropping industry are nitrous oxide (N2O) and carbon dioxide (CO2 ). Fertilizer use accounts for 42% of Alberta's cropping related N2O emissions. Other sources of N2O include manure, compost, legumes, plant residue decomposition and soil organic matter decomposition (especially in fallow years). Current methods used to estimate national N2O emissions from agricultural soils are about plus or minus 40% accurate.
Whatever the form of nitrogen added to or existing in soil, it is susceptible to N2O loss through the processes of nitrification or denitrification, both of which are mediated by soil microorganisms. Denitrification in waterlogged soil conditions is of particular concern because it can be affected by management, while nitrification is the normal process for conversion of soil ammonium (NH4) to soil nitrate (NO3).
The loss of N2O represents a loss of costly nitrogen inputs; therefore it makes environmental and economic sense for producers to increase their nitrogen use efficiency. If Alberta producers implement N2O emission reduction strategies, the amount of gaseous nitrogen losses can easily be reduced by 10 to 20%. Utilizing all of the tools available can cut emissions in the future.
Carbon dioxide emissions from agricultural soils have declined in both Alberta and Canada due to increased soil organic matter from the increase in no-tillage acres and reduced summer fallow acres. Carbon dioxide emissions are expected to continue to decline due to an increase in conservation farming management practices, leading to improved soil quality and reduction of CO2 emissions.
Reducing emissions from fertilizers
By using a number of currently available management practices and technologies, nitrogen use efficiency can be improved, reducing the amount of N2O emissions. These practices relate to right rate, right time and right place.
Matching the nitrogen fertilizer rate to crop needs, while accounting for the soils ability to supply nitrogen is an important first step to reduce potential losses. Promoting balanced nutrient fertilization, where nutrient additions match removals, is also important. For example, Alberta Agriculture research results indicated that farmers using sulpher fertilizer in deficient soils increased crop yields and increased crop nitrogen uptake. Therefore, the risk of nitrogen loss from the system is reduced.
Timing the nitrogen application to coincide with crop uptake helps to reduce the chance for losses. For example, if soil conditions are conducive to N2O loss, changing from fall nitrogen application to a spring application will reduce N2O emissions in Alberta cropping systems between 30 and 50%. If fall applications are required, applying anhydrous ammonia or urea based fertilizer as late as possible, will help reduce the presence of nitrate during the vulnerable winter – early spring thaw period.
Placing the fertilizer below the soil surface with banding operations have been shown to reduce N2O emissions up to 20%compared to surface broadcast applications. Other strategies to further reduce the potential for N2O emissions may include the use of controlled release fertilizer formulations, site specific nutrient application, split applications of nitrogen and appropriate fertilizer placement.
Reducing emissions from cropping practices
Carbon dioxide emissions from Alberta's cropping industry result from burning of fossil fuels and situations where soil organic matter (carbon) decomposition exceeds additions through crop growth or animal waste additions. Using management practices that increase plant residues or slow the rate of organic matter decomposition (such as reduced tillage), will reduce CO2 emissions and improve soil quality.
It is estimated that reducing tillage increases soil carbon sequestration from 0.08 to 0.54 tonnes CO2 equivalent per hectare per year. Reducing tillagealso lowers fuel usage and costs, further reducing CO2 emissions.
Reducing the frequency of fallow and leaving adequate crop residue cover, including the elimination of straw burning, also reduces CO2 emissions.
Opportunity for cropping industry to increase soil carbon
Alberta's cropping industry is in a unique position because of its ability to 'capture' atmospheric carbon in growing crops and then store a portion of that carbon in soil organic matter. Through photosynthesis, CO2 is removed from the atmosphere by plants and stored in the soil, through roots and residue input. This process is known as carbon sequestration or carbon storage. Agricultural soils can be a source (emitting CO2) or a sink (storing CO2) of carbon, depending on the management of that soil.
Broadly speaking, any management practice that increases yield will increase carbon storage in soil. Future actions should therefore include practices such as minimum to no tillage, reduced summer fallow and proper straw management.
Conservation farming practices, such as direct seeding to conserve moisture, that improve yield potential, reduce erosion and reduce fuel costs, also increase soil carbon. Other practices that reduce CO2 emissions and increase soil carbon include field shelterbelts, rotational grazing, perennial forage crops and reduced tillage. Using higher yielding crops or varieties and maximizing yield potential can also increase soil carbon. Irrigation also improves crop growth and can therefore increases soil carbon, depending on the crop rotation.
Opportunities for nitrous oxide reduction
Nitrous oxide has a global warming potential approximately 310 times higher than CO2, over a period of 100 years. The key to reducing N2O emissions from the cropping industry is to continue recommended nitrogen fertilizer management strategies in Albertaincluding right rate, right time and right place. Simultaneously, more research and extension should be done on proper crop rotations (legume-cereals) to reduce nitrogen fertilizer input, precision farming to manage variation of soil fertility, and use of slow release fertilizers in areas where potential for N2O loss is high. Manure application should be based on crop requirements with due care and attention to minimize the potential for surface runoff .
Governments and consumers are expecting all industries, including the cropping industry, to reduce GHG emissions. Increased adoption of conservation farming and best management fertilizer practices could significantly reduce the cropping industry's emissions. As well, promising methods to reduce emissions should be investigated for Alberta conditions . Reducing emissions and increasing soil carbon sequestrationcan improve the industry's production efficiencies, enhance soil and water resources, and contribute to efforts to slow global warming.
- Agriculture and Agri-Food Canada. 1998. The Health of Our Air: Toward sustainable agriculture in Canada. Agriculture and Agri-Food Canada.
- AAFRD Greenhouse Gas Team. 1999. Agriculture and Agri-Food Industry Greenhouse Gas Emissions in Alberta Summary Statement.
- Boehm, M.M., S.N. Kulshreshtha, R.J. MacGregor, B. Junkins, R. Desjardins, and B. McConkey. 2000. Sink potential of carbon sequestering agriculture activities.
- Environment Canada, Canada’s Greenhouse Gas Inventory 1990-2005, Greenhouse Gas Division, Government of Canada, April 2007.
- Environment Canada. 1997. Global Climate Change, "The Science of Climate Change".
- 1999. Reducing Nitrous Oxide Emission From Agro Ecosystems. InternationalN0 Workshop, March 3-5. Banff, Alberta.
- Government of Canada. 2008. Turning the Corner – “Taking Action to Fight Climate Change”. http://www.ec.gc.ca/doc/virage-corner/2008-03/pdf/572_eng.pdf
Information provided by Rob Dunn, Conservation Cropping Specialist. Alberta Agriculture and Rural Development