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Soil respiratory quotient determined via barometric process separation combined with nitrogen-15 labeling

Research Archive

Soil respiratory quotient determined via barometric process separation combined with nitrogen-15 labeling

Müller, C. ; Abbasi, M. K. ; Kammann, C. ; Clough, T. J. ; Sherlock, R. R. ; Stevens, R. J. ; Jäger, H.-J.
Type: Journal Article
Permalink: https://hdl.handle.net/10182/541
Originally published: 2004 by Soil Science Society of America and available at https://doi.org/10.2136/sssaj2004.1610
Rights: Copyright © 2004 Soil Science Society of America
Keywords: gross nitrification rates; barometric process separation (BaPS); ¹⁵N labeling technique; soil respiratory quotient; Agronomy & Agriculture
Fields of Research: 05 Environmental Sciences; 06 Biological Sciences; 07 Agricultural And Veterinary Sciences

Abstract:

The barometric process separation (BaPS) and ¹⁵N dilution techniques were used to determine gross nitrification rates on the same soil cores from an old grassland soil. The BaPS-technique separates the O₂ consumption into that from nitrification and that from soil organic matter (SOM) respiration. The most sensitive parameter for the calculations via the BaPS technique is the respiratory quotient (RQ = ∆CO₂/∆O₂) for SOM turnover (RQSOM). Combining both methods (BaPS–¹⁵N ) allowed the determination of the RQSOM. The RQ value determined in such a way is adjusted for the influence of nitrification and denitrification, which are both characterized by totally different RQ values. The results for the grassland soil showed that 6 to 10% of O₂ was consumed by nitrification when incubated at 20°C and 0.49 g H₂O g⁻¹ soil. A set of BaPS measurements with the same soil at various temperature and moisture contents showed that up to 49% of the total O₂ consumption was due to nitrification. The calculated RQSOM values via the BaPS–¹⁵N technique presented here are more closely associated with the overall SOM turnover than the usual net RQ reported in the literature. Furthermore, the RQSOM value provides an overall indication of the decomposability and chemical characteristics of the respired organic material. Hence, it has the potential to serve as a single state index for SOM quality and therefore be a useful index for SOM turnover models based on substrate quality.

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