title: Confirmation of co-denitrification in grazed grassland.
abstract: Pasture-based livestock systems are often associated with losses of reactive forms of nitrogen (N) to the environment. Research has focused on losses to air and water due to the health, economic and environmental impacts of reactive N. Di-nitrogen (N2) emissions are still poorly characterized, both in terms of the processes involved and their magnitude, due to financial and methodological constraints. Relatively few studies have focused on quantifying N2 losses in vivo and fewer still have examined the relative contribution of the different N2 emission processes, particularly in grazed pastures. We used a combination of a high (15)N isotopic enrichment of applied N with a high precision of determination of (15)N isotopic enrichment by isotope-ratio mass spectrometry to measure N2 emissions in the field. We report that 55.8 g N m(-2) (95%, CI 38 to 77 g m(-2)) was emitted as N2 by the process of co-denitrification in pastoral soils over 123 days following urine deposition (100 g N m(-2)), compared to only 1.1 g N m(-2) (0.4 to 2.8 g m(-2)) from denitrification. This study provides strong evidence for co-denitrification as a major N2 production pathway, which has significant implications for understanding the N budgets of pastoral ecosystems.
authors.affiliation: Teagasc, Johnstown Castle, Environmental Research Centre, County Wexford, Ireland.|AgResearch, Ruakura Research Centre, Hamilton, New Zealand.|Soil &Physical Sciences Department, Lincoln University, Christchurch, New Zealand.
authors.forename: Diana R
authors.initials: DR
authors.lastname: Selbie
authors.affiliation: Teagasc, Johnstown Castle, Environmental Research Centre, County Wexford, Ireland.
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Lanigan
authors.affiliation: Agri-Environment Branch, Agri-Food &Biosciences Institute, Belfast BT9 5PX, UK.
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Laughlin
authors.affiliation: Soil &Physical Sciences Department, Lincoln University, Christchurch, New Zealand.
authors.forename: Hong J
authors.initials: HJ
authors.lastname: Di
authors.affiliation: Soil &Physical Sciences Department, Lincoln University, Christchurch, New Zealand.
authors.forename: James L
authors.initials: JL
authors.lastname: Moir
authors.affiliation: Soil &Physical Sciences Department, Lincoln University, Christchurch, New Zealand.
authors.forename: Keith C
authors.initials: KC
authors.lastname: Cameron
authors.affiliation: Soil &Physical Sciences Department, Lincoln University, Christchurch, New Zealand.
authors.forename: Tim J
authors.initials: TJ
authors.lastname: Clough
authors.affiliation: Agri-Environment Branch, Agri-Food &Biosciences Institute, Belfast BT9 5PX, UK.
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Watson
authors.affiliation: Statistics and Applied Physics, Teagasc, Ashtown, Dublin 15, Ireland.
authors.forename: James
authors.initials: J
authors.lastname: Grant
authors.affiliation: Teagasc, Johnstown Castle, Environmental Research Centre, County Wexford, Ireland.
authors.forename: Cathal
authors.initials: C
authors.lastname: Somers
authors.affiliation: Teagasc, Johnstown Castle, Environmental Research Centre, County Wexford, Ireland.
authors.forename: Karl G
authors.initials: KG
authors.lastname: Richards
mesh_terms: D058440:Denitrification; D065948:Grassland; D060434:Herbivory; D009584:Nitrogen / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis
chemical_list: D009609:Nitrous Oxide; D009584:Nitrogen