The Impact of Nitrogen Management Strategies within Grass Based Dairy Systems
Prepared by: Laurence Shalloo, Elodie Ruelle, Karl Richards, Daniel Hawtree, Donal O Brien, David Wall, Michael O’Donovan, Deirdre Hennessy and Pat Dillon
Teagasc, Oak Park, Carlow, Ireland.
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The Department of Agricultural, Food and the Marine (DAFM) requested Teagasc to simulate the impact (environmental and economic) of a number of farm nitrogen (N) mitigation measures in order to inform policy of the best current and potential actions to deliver the catchment-based nitrate load reduction estimated by the EPA in 2021. That resulted in a report published in July 2021 (https://www.teagasc.ie/media/website/publications/2021/Nitrates-Modelling-Final.pdf). In July 2022, DAFM requested Teagasc to undertake further analysis.
The following were requested to be investigated:
- A review of the literature on the impact of land use, farming system, stocking rate, nitrate regulations on water quality on grass based systems in Ireland.
- Trends in water quality from the Agricultural Catchment Programme.
- Reduction in chemical N fertilizer application of approximately 10%, 20% and 30%, i.e. chemical N application rates of 250, 225, 200 and 175 kg/ha.
- Stocking rate reduction - 250 kg N/ha (2.74 cows/ha), 230 kg N/ha (2.50 cows/ha) versus 220 kg N/ha (2.39 cows/ha).
- Proportion of farms and milk that were in each of the different bands from 2020 and 2021.
- Economic consequences of banding if associated with a reduced stocking rate at farm level.