Practical Advice for Slurry Application Strategies for Grassland Systems

Keywords: Manure application, grassland, Ireland, fertiliser replacement value, FRV, nitrogen, farm advice, legislation

Management of animal manures in history has been influenced to varying extents by objectives of maximising nutrient utilisation and minimising environmental impacts. Relatively inexpensive and freely available chemical fertilisers over the past half-century gave rise to a period in which efficient nutrient recycling was not prioritised. However, the emphasis on slurry as a nutrient resource has been re-established following recent increases in fertiliser prices and the increased focus on manure management within European Union (EU) and national environmental policies. Farmers and policy makers are seeking advice and solutions to maximise fertiliser replacement value (FRV) and minimise negative impacts on water and air quality and climate change. This paper focuses on recent research in Ireland on aspects of slurry management. It discusses how slurry management can contribute to achieving the objectives of reducing ammonia (NH₃) emission, increasing nitrogen (N) FRV, and accounting for the residual release of N where slurry is applied annually over long periods. Costs of low emission application methods are also considered, and emerging research on the NFRV of dilute slurry and soiled water is also discussed. Proposals are made for FRV advice for slurry and soiled water applied with different application methods and at different timings. Farmers should prioritise the distribution of slurry around the farm and application rate based on P and K requirements, and then target cooler and moister atmospheric conditions in spring, when nutrient uptake requirements are highest, in order to maximise NFRV. Application methods such as trailing shoe have been shown to be uniformly effective at reducing NH₃ emissions and increasing NFRV across a range of climatic conditions. However, they are a more expensive strategy than targeting suitable climatic conditions with conventional splashplate equipment. Managing application timing to target climatic conditions is, in principle, a cost effective means of increasing NFRV. However, alternative low emission application methods may be necessary where high targets for NFRV are set, or when suitable climatic conditions do not occur so often. The application of this research has had a significant impact on slurry management at farm level in Ireland. While the adoption of low emission application methods has been very low, despite being incentivised in a number of national funding schemes, there has been a large shift in application timing, with the proportion of slurry being applied in spring increasing from 34% in 2003 to 52% in 2009.

S T J Lalor¹, N J Hoekstra¹, P N C Murphy², K G Richards¹ and G J Lanigan¹

¹ Teagasc, Crops Environment and Land Use Programme, Johnstown Castle, Wexford, Ireland.

² Teagasc, Agricultural Catchment Programme, Johnstown Castle, Wexford, Ireland.

34 pages, 6 figures, 2 tables, 75 references.