Tim J. Clough1, Francis M. Kelliher2, and Robert R. Sherlock1. (1) Lincoln University, Agriculture & Life Sciences, PO Box 84, Canterbury, New Zealand, (2) Manaaki Whenua - Landcare Research, Gerald Street, Lincoln, New Zealand
Anthropogenic sources of N2O continue to increase. The Intergovernmental Panel on Climate Change (IPCC) has prescribed guidelines on how to construct inventories. The IPCC guidelines divide agricultural N2O sources into three categories: direct emissions from agricultural land, emissions from animal waste systems, and indirect emissions associated with nitrogen (N) that is removed in biomass, volatilized, leached, or exported from the agricultural land. Each of the three N2O source categories are considered to contribute an equal 1/3 share of the total estimated agricultural N2O source. However, approximately 2/3 of the uncertainty in the total agricultural N2O source is due to the wide range of estimates for indirect N2O emissions. Further knowledge of the fate of N2O in the subsoil is vital in order to improve our understanding of indirect N2O emissions. Previous work has examined the fate of 15N2O commencing with a 15N labelled nitrate pool. We describe a first attempt to introduce 15N2O into the subsoil of soil columns. Soil columns (15 cm I.D. by 90 cm) were packed with a Temuka silt loam soil (Fluvaquentic Endoaquept) that had been sieved to < 0.4 cm, bulk density 0.7 g cm-3. The soil columns were instrumented with silicone tube gas samplers and time domain reflectometry (TDR). Labeled 15N2O was manufactured in the laboratory and introduced at 60 cm depth via passive diffusion from a 2 L flask. The aim was to emulate a denitrification ‘hot-spot' event in the subsoil. The fate of the N2O and its rate of passage through the soil were monitored over time. Finally an irrigation event was applied to investigate the fate of the N2O. Results of this study are reported.
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