Sward composition and soil moisture conditions affect nitrous oxide emissions and soil nitrogen dynamics following urea-nitrogen application

• Published in: The Science of the total environment Vol. 722; p. 137780
• Main Authors: Bracken, Conor J., Lanigan, Gary J., Richards, Karl G., Müller, Christoph, Tracy, Saoirse R., Grant, James, Krol, Dominika J., Sheridan, Helen, Lynch, Mary Bridget, Grace, Cornelia, Fritch, Rochelle, Murphy, Paul N.C.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.06.2020
• Subjects: Multispecies swards; Nitrous oxide; Perennial ryegrass (Lolium perenne); Ribwort plantain (Plantago lanceolata); Soil nitrogen cycling; White clover (Trifolium repens); White clover (Trifolium repens); Perennial ryegrass (Lolium perenne); Ribwort plantain (Plantago lanceolata); Nitrous oxide; Soil nitrogen cycling; Multispecies swards
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.137780

Increased emissions of N2O, a potent greenhouse gas (GHG), from agricultural soils is a major concern for the sustainability of grassland agriculture. Emissions of N2O are closely associated with the rates and forms of N fertilisers applied as well as prevailing weather and soil conditions. Evidence suggests that multispecies swards require less fertiliser N input, and may cycle N differently, thus reducing N loss to the environment. This study used a restricted simplex-centroid experimental design to investigate N2O emissions and soil N cycling following application of urea-N (40 kg N ha−1) to eight experimental swards (7.8 m2) with differing proportions of three plant functional groups (grass, legume, herb) represented by perennial ryegrass (PRG, Lolium perenne), white clover (WC, Trifolium repens) and ribwort plantain (PLAN, Plantago lanceolata), respectively. Swards were maintained under two contrasting soil moisture conditions to examine the balance between nitrification and denitrification. Two N2O peaks coincided with fertiliser application and heavy rainfall events; 13.4 and 17.7 g N2O-N ha−1 day−1 (ambient soil moisture) and 39.8 and 86.9 g N2O-N ha−1 day−1 (wet soil moisture). Overall, cumulative N2O emissions post-fertiliser application were higher under wet soil conditions. Increasing legume (WC) proportions from 0% to 60% in multispecies swards resulted in model predicted N2O emissions increasing from 22.3 to 96.2 g N2O-N ha−1 (ambient soil conditions) and from 59.0 to 219.3 g N2O-N ha−1 (wet soil conditions), after a uniform N application rate. Soil N dynamics support denitrification as the dominant source of N2O especially under wet soil conditions. Significant interactions of PRG or WC with PLAN on soil mineral N concentrations indicated that multispecies swards containing PLAN potentially inhibit nitrification and could be a useful mitigation strategy for N loss to the environment from grassland agriculture. [Display omitted] •Measurement of N2O emissions and N cycling from varying sward compositions.•Post N application (40 kg N ha−1) N2O loss increased with white clover proportion.•N2O emissions from PRG were 2.5 fold higher in wet soil (WFPS > 60%) compared to ambient.•Soil N dynamics suggest denitrification as dominant N2O source when WFPS > 60%.•Plantago lanceolata (forage herb) potentially regulates N cycling pathways.