Chamber Measurements of Soil Nitrous Oxide Flux: Are Absolute Values Reliable

• Published in: Soil Science Society of America journal Vol. 72; no. 2; pp. 331 - 342
• Main Authors: Rochette, P, Eriksen-Hamel, N.S
• Format: Journal Article
• Language: English
• Published: Madison Soil Science Society 01.03.2008; Soil Science Society of America; American Society of Agronomy
• Subjects: accuracy; agricultural soils; Agronomy. Soil science and plant productions; Atmospheric pressure; Biological and medical sciences; design; Earth sciences; Earth, ocean, space; Efficiency; Estimates; Exact sciences and technology; Fluctuations; Fundamental and applied biological sciences. Psychology; gas emissions; greenhouse gases; measurement; measuring devices; Methods; Nitrous oxide; non-flow-through chambers; non-steady-state chambers; Quality control; research equipment; sampling; Soil quality; Soil science; Soils; Studies; Surficial geology; Temperature; Soil science; Earth science
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2007.0215

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.