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The Impact of Nitrogen Management Strategies within Grass Based Dairy Systems

21 July 2021
Type Report

The Department of Agricultural, Food and Marine requested Teagasc to model the impact (environmental and economic) of a number of farm nitrogen 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.

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The Department of Agricultural, Food and Marine requested Teagasc to model the impact (environmental and economic) of a number of farm nitrogen 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. The assessment was confined to nitrate losses from freely draining soils where farming intensity is greater than 130 kg N/ha/year. The following scenarios were requested to be investigated:
1. Chemical N reduction of approximately 10% and 20% i.e. chemical N application rates of 250, 225 and 200 kg/ha.
2. Delaying the first chemical N application in spring from 15 January.
3. Finish final chemical N application in autumn earlier than 15 September.
4. Uneven distribution of chemical N fertilizer across the farm i.e. applying 300 and 350 kg N/ha on the grazing platform.
5. Stocking rate reduction- 250 kg N/ha (2.74 cows/ha) versus 230 kg N/ha (2.52 cows/ha).
6. High platform stocking rates- 340 kg N/ha (3.73 cows/ha) and 430 kg N/ha (4.72 cows/ha).
7. Spreading slurry during the closed period- 12% and 25% of slurry spread during the month of December.
8. Implementations of using precision farming to increase N use efficiency.
9. Options for banding organic N excretion rates for dairy cows.