The vast majority of soil N2O flux data reported in the literature was obtained using non‐flow‐through non‐steady‐state (NFT‐NSS) chambers. Considerable variation in chamber methodology may influence N2O flux measurements, however, raising concerns about the reliability and accuracy of these measurements. The objectives of this study were to determine criteria for assessing the quality of soil N2O flux measurements made using NFT‐NSS chambers, to evaluate NFT‐NSS chamber methodologies used in the scientific literature, and to propose a minimum set of criteria for NFT‐NSS chamber design and deployment methodology. We identified 16 characteristics of chamber methodology and developed four factors contributing to the quality of N2O flux measurements made using NFT‐NSS chambers. We compiled a data set of 356 studies and evaluated the quality of each study against the set of characteristics and factors to determine the confidence in the reported N2O flux. Confidence in the absolute flux values reported in about 60% of the studies was estimated to be very low or low due to poor methodologies or incomplete reporting. The confidence in flux measurements improved with time; however, there were still about 50% of recent studies (2005–2007) with low or very low confidence levels. This study has shown that the quality of soil N2O flux measurements reported in the literature is often poor. While the flux data obtained may be valid for comparisons between situations (e.g., treatments) within a given study, they are often biased estimates of actual fluxes. We propose a minimum set of criteria for reliable soil N2O flux measurements using NFT‐NSS chambers.

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Rochette, P., Desjardins, R. L. andPatteyE. 1991. Spatialandtemporalvariabilityof soilrespiration in agricultural frelds. Can J. Soil Sci. 7l: [189][190][191][192][193][194][195][196]. Chamber measurements of CO2 evolution were made on bare soil, and in maize (1988) and wheat (1989)

. Estimation of N 2 O emissions from agricultural soils in Canada. I. Development of a country-specific methodology. Can. J. Soil. Sci. 88: 641Á654. International initiatives such as the United Nations Framework Convention on Climate Change and the Kyoto Protocol require that countries calculate national inventories of their greenhouse gas emissions. The objective of the present study was to develop a country-specific (Tier II) methodology to calculate the inventory of N 2 O emissions from agricultural soils in Canada. Regional fertilizer-induced emission factors (EFreg) were first determined using available field experimental data. Values for EFreg were 0.0016 kg N 2 O-N kg(1 N in the semi-arid Brown and 0.008 kg N 2 O-N kg N(1 in the sub-humid Black soil zones of the Prairie region, and 0.017 kg N 2 O-N kg (1 N in the humid provinces of Quebec and Ontario. A function relating EFreg to the ''precipitation to potential evapotranspiration'' ratio was determined to estimate annual emission factors (EFeco) at the ecodistrict scale (:150 000 ha) in all agricultural regions of Canada. Country-specific coefficients were also developed to account for the effect of several additional factors on soil N 2 O emissions. Emissions from fine-textured soils were estimated as being 50% greater than from coarse-and medium-textured soils in eastern Canada; emissions during winter and spring thaw corresponded to 40% of emissions during the snow-free season in eastern Canada; increased emissions from lower (wetter) sections of the landscape and irrigated areas were accounted for; emissions from no-till soils were 10% greater in eastern, but 20% lower in western Canada than from those under conventional tillage practices; emissions under summerfallow were estimated as being equal to those from soils under annual cropping. This country-specific methodology therefore accounts for regional climatic and land use impacts on N 2 O emission factors, and includes several sources/offsets that are not included in the Intergovernmental Panel on Climate Change (IPCC) default approach. For personal use only.

The Intergovernmental Panel on Climate Change (IPCC) standard methodology to conduct national inventories of soil N 2 O emissions is based on default (or Tier I) emission factors for various sources. The objective of our study was to summarize recent N 2 O flux data from agricultural legume crops to assess the emission factor associated with rhizobial nitrogen fixation. Average N 2 O emissions from legumes are 1.0 kg N ha À1 for annual crops, 1.8 kg N ha À1 for pure forage crops and 0.4 kg N ha À1 for grass legume mixes. These values are only slightly greater than background emissions from agricultural crops and are much lower that those predicted using 1996 IPCC methodology. These field flux measurements and other processlevel studies offer little support for the use of an emission factor for biological N fixation (BNF) by legume crops equal to that for fertiliser N. We conclude that much of the increase in soil N 2 O emissions in legume crops may be attributable to the N release from root exudates during the growing season and from decomposition of crop residues after harvest, rather than from BNF per se. Consequently, we propose that the biological fixation process itself be removed from the IPCC N 2 O inventory methodology, and that N 2 O emissions induced by the growth of legume crops be estimated solely as a function of crop residue decomposition using an estimate of above-and below-ground residue inputs, modified as necessary to reflect recent findings on N allocation.