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Nutrient Management
Nitrous oxide (N2O) is the most potent agricultural greenhouse gas. Its global warming potential is 310 times greater than that of carbon dioxide. In Manitoba, nitrous oxide accounts for 55 percent of all agricultural greenhouse gas emissions.
Use of both manure and inorganic fertilizers can result in nitrous oxide emissions.
Nitrous oxide can be produced directly from decomposing manure, either in storage or on the field. It can also be produced through denitrification—the conversion of plant-available nitrogen to gases (including N2O).
Site characteristics, tillage and fertilizer type and placement will all affect the relationship between the amount of nitrogen-based inorganic fertilizer applied and the level of nitrous oxide emissions. It is common that only 50 percent of the nitrogen supplied by inorganic fertilizer is utilized by the crop in the year of application. What happens to the remaining nitrogen is unclear, but approximately 1–2 percent of it may be lost as nitrous oxide. (1)
Following good management practices for both manure and inorganic fertilizers can go a long way to reducing nitrous oxide emissions.
This improved efficiency will not only reduce emission rates of nitrous oxide, but for inorganic fertilizers will also indirectly reduce carbon dioxide emissions from their manufacture. And it should represent economic savings, too.
For manure application, many of the following practices are already required by Manitoba’s Livestock Manure and Mortalities Management Regulation. (2)
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Soil testing
The first step toward reducing nitrous oxide emissions from crop land is annual soil testing for residual nutrient levels. Some nutrients, such as nitrogen and sulphur, can vary greatly from year to year. A soil test will determine appropriate nutrient application rates to maximize yield. (3)
For the Canadian Prairies, soil testing can occur in spring or fall (once soil temperatures are low).
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Excess fertilizer
Crops have varying requirements for nutrients. So if nitrogen is matched to the needs of a particular crop, there will be much less potential for excess residual nitrogen to be converted to nitrous oxide if the soil becomes saturated.
Further benefits of proper application rates include optimal crop response, reduced crop lodging, reduced nutrient loading to the soil, and reduced fertilizer costs. (4)
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Fertilizer incorporation
Injection or immediate incorporation of fertilizer has various environmental benefits, including prevention of direct nitrous oxide loss. (5)
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Application timing
Ideally, fertilizers should be applied as close as possible to the time that plants need the nutrient. Applications in spring will avoid the presence of nitrate-nitrogen during wet spring thaw conditions, when denitrification is more likely. (6) But late fall applications when the soil is cooled are also acceptable. (7)
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Precision farming
Precision farming techniques use new technologies, such as global positioning system (GPS) and geographic information systems (GIS), to identify different soil management zones and corresponding yields. This technology allows the farmer to determine and apply the appropriate rate of inputs to maximize return for each soil management zone.
Precision farming could reduce nitrous oxide emissions by allowing farmers to apply fertilizers only where they are needed and at appropriate application rates. (8) Guidance systems decrease the amount of equipment overlap, reducing inputs applied, and further reducing costs.
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Manure Management
Some additional practices relate directly to manure management. These suggestions will also contribute to reducing nitrous oxide emissions, the most powerful agricultural greenhouse gas.
Manure testing
Manure testing should be done routinely to determine the amount of available nutrients, particularly nitrogen and phosphorus. (9) Future legislation may require manure application to be based on the manure’s phosphorus content, not the nitrogen content. However, generally, nutrient testing will still allow nitrogen levels to be well managed to meet—but not exceed—crop nutrient requirements.
Equipment calibration
To ensure the proper amount of manure is applied based on a target application rate, application equipment should be calibrated. For liquid manure, this can be done with drag-line or tanker application systems equipped with flow-rate monitors. (10)
Winter spreading
The elimination of winter manure spreading will help prevent runoff and spring nitrous oxide emissions.
When manure is applied in spring or after crop emergence, the developing crop will be able to use the nitrogen as it becomes available with minimal risk of loss to the environment. (11)
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Inorganic Fertilizer Management
Some further practices relate directly to inorganic fertilizer management. These suggestions will also contribute to reducing nitrous oxide emissions.
Fertilizer banding
The best method of nitrogen application is banding. Nitrogen applied in a concentrated band is less susceptible to denitrification. If banding is not possible, then ensure that the nitrogen fertilizer is incorporated into the soil shortly after application. (12)
Slow-release nitrogen fertilizer
A fertilizer that releases its nutrient slowly over time will make nitrogen available to the crop when it is most needed, and reduce leaching and denitrification. (13) These fertilizers are more expensive, however, so economics may limit their use to high-value crops.
Urease inhibitors and nitrification inhibitors
Urease inhibitors prevent volatilization (gassing off) of surface-applied urea. A nitrification inhibitor slows the conversion of ammonia-nitrogen to nitrate-nitrogen. This reduces the risk of nitrogen losses from a variety of paths, including nitrous oxide emissions from denitrification. (14)
Urease and nitrification inhibitors improve the efficiency of nitrogen uptake and are more affordable than slow-release fertilizers, but also improve the efficiency of nitrogen. (15)
