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Challenges and Opportunities for Sustainable Nitrogen Management in Dairy Systems
Lakhanpal, Garima
Lakhanpal, Garima
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2025
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Garima Lakhanpal (2020). Challenges and Opportunities for Sustainable Nitrogen Management in Dairy Systems. University of Waterloo (Canada).
Abstract
Nitrogen (N) is central to agricultural productivity, yet its mismanagement drives water and air pollution across the world. Ireland’s grass-based dairy systems are among the most Nintensive in the European Union (EU), with high inorganic and organic fertilizer sustaining productivity but creating persistent surpluses that threaten groundwater and surface water quality. Despite major policy efforts, Ireland continues to struggle to meet EU Water Framework Directive (WFD) chemical targets for good water status. However, Ireland is still seeking the renewal of its Nitrates Derogation, which allows exceptionally high stocking rates up to 220 kg N ha⁻¹ yr⁻¹. This tension between economic needs and environmental compliance defines one of the country’s greatest agri-environmental challenges. The EU is moving toward tighter nutrient limits and nature restoration objectives, making it essential to understand whether sustainable dairy production can coexist with future regulatory expectations.
One of the main obstacles to achieving water-quality goals is the temporal disconnect between management interventions and measurable improvements, which can erode stakeholder confidence and obscure the true impact of mitigation policies. In Ireland, the EU WFD program of measures (PoMs) is carried out under the Nitrates Directive, which include nutrient management, land management and farmyard management strategies to protect water quality. These lags are increasingly attributed to legacy N i.e., reactive N accumulated in soils and subsoils from past surpluses that continue to leach long after inputs decline. While
groundwater legacy effects are recognized (i.e., the time it takes water to travel through the soil termed hydrologic time lag), few studies worldwide have directly quantified soil legacy N (i.e., biogeochemical time lags), and none had done so in Ireland prior to this research. Understanding the scale, distribution, and persistence of these soil pools is critical for designing realistic mitigation timelines and adaptive policies.
The overarching aim of my research was therefore to assess N dynamics and environmental outcomes in Irish dairy systems by evaluating mitigation scenarios and quantifying legacy soil N accumulation to understand how current and historical management, drainage class, and hydrogeological setting influence both near-term losses and the pace of environmental recovery. I combined process-based modelling, multi-decadal farm data, deep soil coring, and groundwater monitoring to connect farm management decisions with both short- and long-term system responses. Together, these studies form the first integrated assessment of soil N legacies in Irish dairy systems