Should international protocols be ratified, New Zealand will become legally committed to limit its greenhouse gas emissions The three major greenhouse gases are carbon dioxide (CO ₂ ), methane (CH ₄ ), and nitrous oxide (N ₂ O) Agricultural soils are generally considered to be the main source of N ₂ O emissions in New Zealand, but production estimates to date are surrounded by great uncertainty This paper reviews our current understanding of agricultural N ₂ O emissions, and suggests directions for future research needs by evaluating the default emission factors of the 1996 Revised Guidelines for National Greenhouse Gas Inventories of the Intergovernmental Panel on Climate Change (IPCC) for the New Zealand situation The emission factors calculated for New Zealand agricultural soils are generally within the range of the 1996 IPCC default values, but the limited amount of research data available hampers a full evaluation of the appropriateness of these factors for New Zealand More long‐term studies are needed to refine our emission factors, particularly those for animal urine and dung returned to pasture Application of the IPCC methodology to New Zealand identifies herbivore excrement as the single largest potential source of anthropogenic N ₂ O emissions (about 50% of the total emission) In addition, research is also required for indirect sources of N ₂ O, because only limited overseas data, and none from New Zealand, are available The 1996 IPCC methodology does not account for variations in climatic and soil physical conditions, which are known to affect N ₂ O emissions In the longer term, development of robust process‐based models, coupled with spatial and temporal data sets of the major drivers of N ₂ O emissions, may therefore be a useful approach for obtaining national emission estimates for New Zealand This will require long‐term monitoring of N ₂ O emissions, under various land uses and on a national network of sites

Nitrous oxide (N2O) emissions from agricultural soils have been estimated to comprise about two-thirds of the biosphere’s contribution of this potent greenhouse gas. In pasture systems grazed by farmed animals, where substrate is generally available, spatial variation in emissions, in addition to that cause by the patchiness of urine deposition, has been attributed to soil aeration, as governed by gas diffusion. However, this parameter is not readily measured, and the soil’s water-filled pore space (WFPS) has often been used as a proxy, despite gas diffusion in soils depending on the volumetric fractions of water and air. With changing water content, these fractions will reflect the soil’s pore size distribution. The aims of this study were: (i) to determine if the pore size distribution of two pastoral soils explains previously observed differences in N2O emissions under field conditions, and (ii) to assess the most appropriate soil water/gas diffusion metric for estimating N2O emissions. The N2O emissions were measured from intact cores of two soils (one classified as well drained and one as poorly drained) that had been sampled to a depth of 50 mm beneath grazed pasture. Nitrogen (N, 500 kg N/ha) was applied to soil cores as aqueous nitrate solution, and the cores were drained under controlled conditions at a constant temperature. The poorly drained soil had a larger proportion of macropores (23.5 v. 18.7% in the well-drained soil), resulting in more rapid drainage and increased pore continuity, thereby reducing the duration of anaerobicity, and leading to lower N2O emissions. Emissions were related to three soil water proxies including WFPS, volumetric water content (VWC), and matric potential (MP), and to relative diffusion (RD). All parameters showed highly significant relationships with N2O emissions (P < 0.001), with RD, WFPS, VWC, and MP accounting for 59, 72, 88, and 93% of the variability, respectively. As VWC is more readily determined than MP, the former is potentially more suitable for estimating N2O emission from different soils across a range of time and space scales under field conditions.

Nitrous oxide (N₂O) emissions are highly episodic in response to nitrogen additions and changes in soil moisture. Automated gas sampling provides the necessary high temporal frequency to capture these emission events in real time, ensuring the development of accurate N₂O inventories and effective mitigation strategies to reduce global warming. This paper outlines the design and operational considerations of automated chamber systems including chamber design and deployment, frequency of gas sampling, and options in terms of the analysis of gas samples. The basic hardware and software requirements for automated chambers are described, including the major challenges and obstacles in their implementation and operation in a wide range of environments. Detailed descriptions are provided of automated systems that have been deployed to assess the impacts of agronomy on the emissions of N₂O and other significant greenhouse gases. This information will assist researchers across the world in the successful deployment and operation of automated N₂O chamber systems.