Ernest Osei-Asante's research investigates how optimising livestock diets can mitigate urine nitrogen emissions. By understanding nitrogen loss pathways and exploring practical interventions, Ernest (UCD School of Agriculture and Food Science Doctoral Researcher and Teagasc Walsh Scholar) aims to identify solutions that balance environmental sustainability with agricultural productivity.
N is for Nitrogen
Nitrogen emissions from agriculture significantly impact soil, air and water quality. Surprisingly, an everyday process in livestock farming - urination - plays a significant role. Each urine deposit on pasture releases nitrogen compounds, which, if unmanaged, contribute to ammonia, nitrous oxide, and nitrate emissions.
My research investigates how optimising livestock diets can mitigate urine nitrogen emissions. By understanding nitrogen loss pathways and exploring practical interventions, UCD School of Agriculture and Food Science Doctoral Researcher and Teagasc Walsh Scholar Ernest Osei-Asante aims to identify solutions that balance environmental sustainability with agricultural productivity.
My research examines how adjusting livestock diets and management practices can lower nitrogen emissions. Specifically, I:
- Quantify Emissions from Urine Patches: I use chambers and gas analysers to measure ammonia and nitrous oxide emissions directly from soil treated with different urine nitrogen concentrations.
- Test Mitigation Strategies: I evaluate the effectiveness of adjusting protein content in the feed and integrating multispecies swards into pastures.
- Model Nitrogen Dynamics: I will use models to predict nitrogen emissions under various management scenarios, providing insights for policy and practice.
My research aims to provide actionable solutions for farmers and policymakers by linking laboratory experiments with field trials.
Current Context: The Nitrates Directive and Derogation
The European Union’s Nitrates Directive safeguards water quality by regulating agricultural nitrogen inputs. Ireland’s derogation under this directive allows specific farms to exceed the 170 kg of nitrogen per hectare annual limit, provided they implement stricter environmental measures.
Recent reports show increasing nitrate pollution in Irish water bodies, leading to debates about the derogation's future. Reducing derogation limits or phasing them out could have significant implications for intensive livestock systems.
My research supports this discussion by offering strategies to reduce nitrogen losses at the farm level. By targeting emissions from urine patches - a significant nitrogen source - farmers can comply with environmental regulations while maintaining productivity.
Nitrogen Cycle in a grazed pasture system
When livestock graze on pasture, their urine adds nitrogen, mainly urea, to the soil. Soil microbes quickly convert urea into ammonium. This raises the nitrogen content in that patch of soil to levels far above what plants can absorb. This excess nitrogen follows different pathways in the soil and environment, leading to:
- Ammonia (NH3): A gas that volatilises from the soil surface, contributing to air pollution and biodiversity loss in nearby areas.
- Nitrous Oxide (N2O): A potent greenhouse gas produced when microbes convert nitrogen under low-oxygen conditions in the soil.
- Nitrate (NO3-): A compound that can leach from the soil into waterways, posing risks to water quality.
These emissions are particularly pronounced in "urine patches," which act as nitrogen hotspots. We can develop strategies to curb nitrogen losses and lessen agriculture’s environmental footprint by targeting these patches.
Nitrogen Cycle and Emissions in grazed pasture systems. Credit: De Klein et al., 2008.
Why Urine Nitrogen Concentration Matters
The nitrogen concentration in livestock urine varies based on the animal’s diet, species, and overall management practices. Diets high in protein, for example, increase the nitrogen content in urine, leading to more intense nitrogen loading in soil. Here’s how this impacts each emission pathway:
- Ammonia Emissions: The high nitrogen concentration creates a fertile ground for rapid conversion of urea to ammonia, which then volatilises. This wastes nitrogen that plants could otherwise use. It also contributes to air pollution that can drift to nearby areas and damage sensitive ecosystems.
- Nitrous Oxide Emissions: As nitrogen concentration rises in the soil, microbes convert the excess into nitrous oxide, particularly in low-oxygen conditions. Wet soils, for instance, support the denitrification process, resulting in significant greenhouse gas emissions.
- Nitrate Leaching: Nitrate, a water-soluble form of nitrogen, can leach beyond the root zone, especially after rainfall. High nitrogen concentrations increase the risk of groundwater contamination and eutrophication in water bodies. This can lead to algal blooms and oxygen-depleted zones that harm aquatic life.
These impacts illustrate why managing urine nitrogen concentration is crucial. Without intervention, concentrated nitrogen leads to losses affecting farm productivity and the environment.
Strategies to Mitigate Nitrogen Emissions from Livestock Urine
Reducing nitrogen emissions from livestock urine is possible through dietary adjustments, grazing management, and soil amendments.
- Adjusting Animal Diets: Balancing protein intake reduces nitrogen excretion in urine. Livestock that consume more protein than is necessary for growth and maintenance excrete the excess nitrogen in their urine. Adjusting the diet to meet but not exceed protein requirements lowers the nitrogen load per urine patch, reducing emissions.
- Adopting Multispecies Swards: Integrating grasses, legumes, and herbs in pastures enhances nitrogen uptake. Deep-rooted species like plantain and chicory access nitrogen from deeper soil layers, reducing leaching risks.
- Grazing Management: Rotational grazing, where livestock are moved frequently, prevents nitrogen from building up in specific areas. This allows plants to use the nitrogen before emissions have a chance to increase.
- Use of Soil Amendments: Adding nitrification and urease inhibitors can slow nitrogen conversion processes in the soil. This helps reduce both ammonia volatilisation and nitrous oxide production.
Focusing on strategies to lower urine nitrogen emissions helps agriculture adopt more sustainable practices. Reducing emissions is not just about environmental responsibility but also about improving farm nitrogen use efficiency. Every molecule of nitrogen lost to the atmosphere or water systems represents a missed opportunity for soil and crop health. Therefore, efficient nitrogen management is a win-win for farmers and the planet.
Conclusion
Urine nitrogen emissions are a manageable aspect of agriculture’s environmental footprint. We can tackle emissions at the source by focusing on diet, grazing, and soil management.
As the Nitrates Directive discussions continue, my research highlights practical ways to meet environmental targets while ensuring farm productivity. Small changes in agricultural practices can yield substantial environmental benefits, paving the way for a more sustainable future.
Essay first published 10 December 2024.
About the author
Ernest Osei-Asante is a PhD candidate at University College Dublin, working under the PASTURE NUE Project as a Teagasc Walsh Scholar. His research focuses on optimising nitrogen levels in animal diets to reduce environmental nitrogen emissions. This work aims to contribute to more sustainable practices in livestock farming. Ernest holds a Master’s in Soil Science from Massey University, New Zealand, where he studied under the New Zealand Development Scholarship program.
See his LinkedIn and X for further information.
About the series
The A-Z of Environmental, Climate and Sustainability Research is a new series of short essays by UCD postdoctoral and postgraduate researchers, technical and research support staff, about their work. The series is developed and curated by the Earth Institute Associate Member Committee and Earth Institute staff. If you'd like to submit a piece for the series do get in touch!
Find out more about the Anthropocene with Nick Scroxton, Bees with Katherine Burns, Cannabis with Caroline Dowling, Degrowth with Ciarán O'Brien, Education with Georgina Fagan, Finance with Shane McGuinness, Gaia with Federico Cerrone, Hydrometry with Kate de Smeth, Innovation with Hannah Gould, Justice with Lauren Minion, Kelp with Priya Pollard, Landscape part 1 with Tomas Buitendijk, Landscape part 2 with Amy Strecker and Amanda Byer, Reusing microbial ‘bathwater’ for sustainable drug production with Laura Murphy, Mammals with Virginia Morera-Pujol, and Nitrogen with Ernest Osei-Asante in our latest essays.
Further reading
Use of a urease inhibitor to mitigate ammonia emissions from urine patches by Rodriguez et al., 2021 in the Journal of Environmental Technology.
Greenhouse gas emissions. In Environmental Impacts of Pasture-Based Farming (pp. 1-32) by De Klein et al., 2008.
Water quality and monitoring report on nitrogen and phosphorus concentrations in Irish Waters 2023 by the Environmental Protection Agency (EPA), Ireland.
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