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Manure management
Approximately 25% of Manitoba’s agricultural emissions are attributed to manure. (1)
Emissions from manure come in the form of methane (decomposition of manure during storage and application) and nitrous oxide (manure storage and application).
Greenhouse gas emissions from manure are influenced by a variety of factors, such as temperature, oxygen level (aeration), moisture and sources of nutrients. These factors are in turn affected by manure type, diet, storage and handling of manure, and manure application. (2) Determining how best to reduce these emissions is complicated and problematic.
Changing storage systems is an expensive step that produces only moderate emissions reductions and it is not yet clear which system is the best for managing manure emissions. (3)
However, this section will give some suggestions on manure handling, storage and application practices that should also have positive environmental effects.
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Manure handling systems in barn
Ensuring that manure is quickly removed from the barn to enclosed storage areas will cut emissions from the barn itself. Manure kept in the barn will tend to be warmer than manure stored outdoors, and will produce more methane. (4) Barn scraper systems can provide regular manure removal from the barn. (5)
In solid manure management systems, where poultry and livestock are housed on dry bedded manure packs of straw, sawdust, etc., lower methane emissions have been noted. (6)
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Manure storage systems
What to do with manure once it has been removed from the barn is a more complicated question. More research is needed to determine the best storage systems and methods, but there are some good starting points.
- It is best to avoid liquid or slurry handling systems. Methane production takes place when manure decomposes in the absence of oxygen (anaerobic conditions). Therefore, methane production is higher in liquid manure. (7)
- Manure storage covers—roofs for solid, covered tanks for liquid, etc.—can be used to trap manure gases. In liquid systems covers may reduce methane emissions by up to 95 percent. (8) They also have the added benefit of controlling odour. (9) It is unclear what happens to the trapped gases when that manure is applied to fields. (10)
- Straw covers should be avoided. Using a straw cover may be an effective odour barrier, but when the straw sinks into liquid manure storage—as often happens during wind or rain—it adds carbon, which can increase methane production substantially. (11)
- Manure shouldn’t be stockpiled for long periods. It can lead to anaerobic decomposition, resulting in both methane and nitrous oxide emissions. (12)
- Temperatures should be kept as low as possible while storing manure. This can be done with below-ground tanks. (13) Below-ground tanks must—like all manure storage facilities in Manitoba—be designed and constructed under the supervision of a professional engineer. (14)
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Compost
Composting has a number of environmental benefits. It breaks down manure into a more stable organic form and is rich in carbon, free of most pathogens and weed seeds, and enhances soil. It also has benefits related to surface and groundwater quality and ammonia emissions. (15) As well, since manure volume is significantly reduced, less fossil fuel is needed for field applications. (16)
However, more research is needed to determine whether composting manure results in a net greenhouse gas benefit.
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Anaerobic digesters
Digesters or other technology for recycling methane from manure to generate energy have good potential to harness methane gas produced on the farm while also displacing fossil fuel energy sources.
Anaerobic digesters process liquid manure by heating and mixing it continuously, in the absence of oxygen, to produce high levels of methane gas (biogas). The biogas can then be used as a fuel in power generators, engines, boilers and burners. The remaining effluent from the digester has some nutrient value but fewer odours than stored manure and can be applied on fields as a fertilizer.
These systems have traditionally been much too expensive for most farmers to consider, but they could hold potential in the future under the right policy and economic conditions. (17) In December 2006 the Manitoba government committed $300,000 for biogas research on Manitoba hog farms.
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Manure application
Manure application has been extensively covered under the Crop section on this website. However, the following suggestions should be useful for livestock operations as well.
- Manure should be applied to soil as soon as possible after it is collected. Storing manure for long periods can encourage anaerobic decomposition and lead to increased methane emissions. (18)
- Injecting or incorporating manure as soon as possible after application will reduce nitrogen loss. (19)
- Applying manure in areas where the soil can become saturated should be avoided, as this also leads to anaerobic decomposition and increased nitrous oxide emissions. (20)
- Eliminating winter applications (now restricted under Manitoba’s Livestock Manure and Mortalities Management Regulation) will reduce the risk of run-off, and reduce the amount of nitrate-nitrogen in soils during spring snowmelt when the risk of nitrous oxide losses are the greatest. (21)
- Spreading manure uniformly around pasture will reduce nitrogen losses. (22)
- Moving winter feeding and bedding areas around pastures will ensure manure is more evenly distributed. This will result in better decomposition. (23)
- Stationing winter feeding areas on level ground away from riparian areas will reduce the risk of manure run-off entering surface watercourses. (24)
