Manure management

Topping up with manureOn this page, we we discuss the following available manure management technologies:(1)

Click a link in the list above to jump to that topic on this page.

A great resource to understanding everything about manure are the Tri-Provincial Manure Application and Use Guidelines.(2)

Nutrient management is particularly important in Manitoba due to the large expansion of the hog industry over the last few decades. Although manure is an excellent source for plant nutrients, the expansion to more than 8 million hogs in 2010 has resulted in the challenge of too much manure and not enough land-base for spreading.(3) The large amount of manure created and the resulting nitrous oxide (N2O) should make manure management a priority when trying to reduce greenhouse gas (GHG) emissions from farms. Approximately 9 percent of Manitoba’s agricultural GHG emissions are created due to manure storage and management.(4)

Major emissions from manure come in the form of methane (CH4) from anaerobic decomposition of manure during storage, and N2O formed during storage and application.

The creation of these gases is influenced by a variety of factors: temperature, oxygen level, moisture or amount of nutrients.

In turn, these factors are affected by manure type, animal diet, the type of manure storage and handling, and manure application techniques.(5) To help reduce GHG creation and work with large amounts of excess manure, it is important that manure management in the province concentrates on disposing manure in an environmentally and economically friendly manner.

Objectives for manure management should focus on maintaining or improving local water and air quality by limiting unpleasant odors, reducing nitrogen (N) and phosphorus (P) concentrations in manure and efficiently spreading manure. Although many management technologies exist, not all are realistic or cheap enough for farmers to implement. Different nutrient management strategies will work better for different farms.

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Manure handling systems

Emissions from manure handling systems are released when favourable conditions are met for gas creation. Warm, wet conditions tend to create higher amounts of both CH4 and N2O.

To reduce gaseous emissions when handling manure ensure that manure is not left in the barn environment for extended periods of time. Manure kept in a barn will tend to be warmer than manure stored outdoors and will produce more methane. Keeping barns clean and dry will help lower the loss of ammonia, reducing N2O production.(6) Barn scraper systems can provide regular manure removal from the barn and store waste in proper storage areas.

Solid manure management systems, where poultry and livestock are housed on dry bedded manure packs of straw or sawdust were found to have lower CH4 emissions when compared to liquid or slurry handling systems.(7)

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Manure storage systems

Manure storage is one of the main areas where a farmer can control how many nutrients remain in or are lost from the manure. It is in the best interest of the farmer to focus on what method of storage system is best for the farm and type of livestock. Certain manure storage systems are more environmentally friendly than others, but may not be the best fit for the type of livestock the farmer is raising.

The following practices are encouraged:

  • Avoid liquid or slurry handling systems – Methane production takes place when manure decomposes in the absence of oxygen (anaerobic conditions). Therefore, CH4 production is higher in liquid manure.(8)
  • Use manure storage covers – roofs for solid, covered tanks for liquid – to trap manure gases. In liquid systems, covers may reduce methane emissions by up to 95 percent.(9) Covers also have the added benefit of controlling odour. Odour means that gas and money is being lost!!
  • Avoid disturbing liquid manures in lagoons – Aerating lagoons increases oxygen and can eliminate CH4 emissions, but increase N2O emissions.(10)
  • Avoid straw covers. Using a straw cover may be an effective odour barrier, but when the straw sinks into the liquid manure it adds C, which can substantially increase CH4 production.(11)
  • Avoid stockpiling manure for long periods – Stockpiling can lead to anaerobic decomposition, resulting in both CH4 and N2O emissions.(12)

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Manure testing

Manure testing should be done routinely to determine the amount of plant-available nutrients, particularly N and P.

Current legislation states that manure application be based on soil nutrient levels:

  • When soil Olsen-P levels are between 60 and 180 ppm, manure can be applied no more than five times the annual crop removal rate of phosphate (P2O5).
  • Additionally, nitrate-N levels can be no more than 140 lbs per acre (157.1 kg/ha) of soil class 1 to 3.(13)

Because both nutrient levels are important in terms of the amount of applied manure, manure testing is a cost-effective farming practice.

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Proper manure application

Timing is everything when it comes to properly applying manure to fields. To ensure that crops receive the most nutrients possible, manure should be applied when crops will use it.

If manure is not taken up by plants, losses will occur through gaseous emissions, leaching or by surface run-off.(14)

The following strategies can help improve manure nutrient use by crops and result in less GHG emissions.

  • Apply manure to fields as soon as possible after removal from storage. Storing manure for long periods can encourage anaerobic decomposition and lead to increased CH4 emissions.
  • Inject or incorporate manure as soon as possible after application to reduce N loss.
  • Avoid applying manure in areas where soil can become saturated, as this leads to anaerobic decomposition and increased N2O emissions.
  • Eliminate winter applications to reduce the risk of run-off, and reduce the amount of nitrate-N in soils during spring snowmelt when risk of N2O loss is greatest.(15)
  • Spread manure uniformly around pasture to reduce N losses.
  • Move winter feeding and bedding areas around pastures so manure is more evenly distributed. This will result in better decomposition.
  • Station winter feeding areas on level ground away from riparian areas. This will reduce the risk of manure run-off entering surface watercourses.(16)

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Eliminate winter spreading

Winter manure application should be eliminated to prevent manure runoff at spring-thaw and to reduce spring-thaw N2O emissions.

Effective November 10, 2013, the spreading of livestock manure between November 10 and April 10 in Manitoba is prohibited under The Environment Act: Livestock Manure and Mortalities Management Regulation, unless otherwise noted.(17)

Applying manure after April 10 encourages farmers to apply manure at a time when their crops are just beginning to grow. The developing crop uses the nutrients as they become plant-available, minimizing the risk of loss to the environment.(18)

Should moving manure during the winter be necessary, it is recommended that the manure be stock-piled in the field and spread following spring-melt.

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Composting manure

Composting breaks manure into a more stable organic form, slowly releasing nutrients over time. Compost is rich in C, free from most pathogens and weed seeds, and improves soil nutrient status. Because compost reduces the amount of synthetic fertilizer needed on fields, composting manure helps lower net GHG emissions from livestock systems. The aerobic (with air) method of decomposing manure is also thought to lower CH4 and N2O creation.(19) However, more research is needed to determine the exact benefit of composting manure net GHG reduction.

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Consider anaerobic digesters

Anaerobic digestion is the oxygen-free process through which manure is broken down by microbes. The microbes produce a mix of CH4 and CO2, called biogas. This biogas can be cleaned and used as a natural gas replacement, burned as fuel or used by a generator to produce electricity or heat.(20) The remaining organic material left after the digestion process has some nutritional value, very little odor and can be applied to fields as fertilizer.

Current anaerobic digesters on the market are much too expensive for most farmers to own. Research continues at the University of Manitoba to determine the benefits of digesters on manure management.(21)

CCC_Livestock_Guide_2013_cover_smThis digestion system works better for dairy and cattle manure, as poultry and swine manure presents more of a challenge due to their higher nitrogen levels.(22) Anaerobic digestion is known to reduce pathogens, odour and weed seeds in the digested manure, reduce GHG emissions and provides an alternative fuel source.(23)

Digesters may be the technology of the future to lower farm fuel consumption or provide alternative energy creation.

For more information, download our publicationFarming in a Changing Climate in Manitoba – Livestock Edition (2013)

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