Simulation of management practices to reduce nitrogen losses to water and air on well-drained grass-based dairy farms in derogation

G Lakhanpal ¹, N B Basu ², D O'Brien ³

⁰Department of Earth and Environmental Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canada; Water Institute, University of Waterloo, Waterloo, ON, N2L 3G1, Canada; Environment Research Centre, Teagasc, Johnstown Castle, Wexford, Co. Wexford, Y35 HK54, Ireland.

Journal of Dairy Science +

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May 14, 2025

View abstract on PubMed

Summary

Reducing nitrogen fertilizer and implementing restricted grazing on Irish dairy farms can significantly minimize environmental losses. These strategies, including protected urea, are key to improving water and air quality while maintaining farm profitability.

Area Of Science

Agricultural Science
Environmental Science
Soil Science

Background

Understanding nitrogen (N) flows in dairy farms is crucial for environmental regulation and policy.
Irish grass-based dairy farms face challenges in managing N to prevent environmental losses.
Derogation farms, stocked at 250 kg N ha<sup>-1</sup>, require strategies to mitigate N surplus and emissions.

Purpose Of The Study

To quantify N flows and losses in a well-drained Irish dairy farm at derogation using the €riN-Moorepark dairy system model (MDSM).
To propose and evaluate alternative management scenarios for minimizing environmental N losses.
To assess the impact of reduced stocking rates, altered fertilizer inputs, protected urea, and restrictive grazing on N losses.

Main Methods

Utilized the €riN-Moorepark dairy system model (MDSM) to simulate N flows and losses.
Simulated various management practices including changes in inorganic and organic fertilizer rates, substitution of calcium ammonium nitrate (CAN) with protected urea, and implementation of restrictive grazing periods.
Quantified nitrate (NO<sub>3</sub><sup>-</sup>), ammonia (NH<sub>3</sub>), nitrous oxide (N<sub>2</sub>O), and dinitrogen (N<sub>2</sub>) emissions.

Main Results

At derogation (250 kg N ha<sup>-1</sup>), the farm N surplus was 241.3 kg N ha<sup>-1</sup>, with leached loads of 46.6 kg N ha<sup>-1</sup> and gaseous emissions of 127.3 kg N ha<sup>-1</sup>.
Reducing stocking rates to 170 kg N ha<sup>-1</sup> and 230 kg N ha<sup>-1</sup> decreased leaching losses by 21.5% and 6.4%, respectively.
Using protected urea reduced NH<sub>3</sub> emissions by 5.2%, and restrictive grazing significantly decreased NO<sub>3</sub><sup>-</sup> leaching, with reductions up to 38.3%.

Conclusions

A combination of reduced fertilizer rates, restricted grazing, and protected urea can significantly minimize nitrogen losses from Irish dairy farms.
Implementing these strategies offers a pathway to achieve better water and air quality outcomes.
Future research should integrate economic assessments with environmental impact studies to ensure the profitability of mitigation strategies for Irish dairy farms.

Keywords:

agriculture environment pollution swapping production

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