The Impact of Nitrogen Management Strategies within Grass Based Dairy Systems

The Department of Agriculture, Food and the Marine (DAFM) 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 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.