Cattle slurry is a significant source of nutrients for grass growth. To reduce ammonia and greenhouse gas emissions as well as retain maximum nitrogen from the slurry, chemically amending the slurry can be useful.
Slurry additives are chemicals which are added to slurry during storage to alter the composition of slurry in such a way that nitrogen retained within the slurry is increased thus reducing GHG losses to the atmosphere.
Why should farmers consider chemically amending their slurry?
Treating slurry with chemicals yields the following benefits:
- More nitrogen will be retained from the slurry thus reducing demand and costs associated with chemical fertiliser.
- Gaseous nitrogen losses will be reduced resulting in lower GHG emissions associated with slurry.
- The treated slurry will have a less pungent smell.
How do you chemically amend slurry?
Teagasc researchers explain how to treat slurry with chemical amendments during storage in the following video.
- Chemicals such as alum, ferric chloride or polyaluminium have been widely used to treat slurry and have been considered effective as they can reduce methane and ammonia emissions during storage and/or at the application of slurry.
- The slurry additives can reduce GHG emissions without increasing the loss of other nutrients such as phosphorus into water bodies or increasing ammonia into the atmosphere (a condition referred to as pollution swapping).
- Slurry chemical amendments used for trials are not yet fully authorized for commercial use
Economic and Environmental Benefits
Treating manure with chemicals such as Glasabate reduces the loss of carbon resulting in fewer emissions. More nitrogen is retained in the manure thus reducing the demand for chemical nitrogen fertiliser and the reduction in fertiliser cost.
In order to quantify the environmental and economic benefits, a case study for a farm with 84 cows housed for 18 weeks during winter was used as shown in Table 8.
Table 8 Net costs of slurry additives and reduction in emissions
Amend 50% of slurry
Amend 100% of slurry
|Total slurry (m3)||499||499|
|Fertiliser savings (€)||60||120|
|Amendment cost (€)||-499||-998|
|Net costs (€)||– 439||-878|
|Total emissions(kg CO2-eq / kg FPCM)||0.94||0.93|
|Reduction in emissions (%)||1.2||2.48|
84 cow herd, soil drainage is moderate
Slurry additive costs 2€/m3 of slurry
Net savings/ cost are the savings or cost per year for the farm
Research at Farm Zero C
Work at Farm Zero C investigated the use of a chemical additive- GasAbate supplied by Glapsortbio, on greenhouse gas emissions stored slurry. GasAbate was injected in slurry tanks at the farm. Floating chambers on slurry surfaces collected gaseous emissions for over 3 weeks after treatment. The pre-treatment concentrations were compared to those taken after treatment with GasAbate.
Key findings from previous research on the use of Slurry Chemical Amendments have yielded different results:
- Acidification of slurry has consistently shown a reduction in GHG emissions during storage (Emmerling et al., 2020).
- Research undertaken at Teagasc, Johnstown Castle and Agri-food and Biosciences Institute (AFBI) found no differences between treated and untreated slurry in terms of organic nitrogen conversion or reducing losses from slurry during application (Wall, 2019.).
- In another study, applying cattle slurry pre-mixed with the nitrification inhibitor dicyandiamide (DCD) during anaerobic storage was shown to potentially reduce nitrous oxide losses by up to 88% as compared to non-treated slurry. In this study, there were high levels of uncertainties in N2O for different chemicals including the commercially available additives (Kavanagh et al., 2021).
- More research is required to ascertain soil health impacts and long-term grass productivity when treated slurry is used.
Links to more research
- Amendment of cattle slurry with the nitrification inhibitor dicyandiamide during storage: A new effective and practical N2O mitigation measure for land spreading
- Greenhouse gas and ammonia emissions from slurry storage
- The Effect of Chemical Amendments Used for Phosphorus Abatement on Greenhouse Gas and Ammonia Emissions from Dairy Cattle Slurry: Synergies and Pollution Swapping.
- Mitigating ammonia and greenhouse gas emissions from stored cattle slurry
Chemically amending slurry helps in reducing nitrogen losses from slurry thus helping farmers in adhering to the following regulations.
The Nitrates and water directive
While most chemical amendment additives are not yet available commercially, the following company is working to further develop these additives: