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Carbon-to-nitrogen ratio
The C/N ratio (C:N) or carbon-to-nitrogen ratio is a ratio of the mass of carbon to the mass of nitrogen in a substance. It can, amongst other things, be used in analysing sediments and compost. A useful application for C/N ratios is as a proxy for paleoclimate research, having different uses whether the sediment cores are terrestrial-based or marine-based. Carbon-to-nitrogen ratios are an indicator for nitrogen limitation of plants and other organisms and can identify whether molecules found in the sediment under study come from land-based or algal plants.〔Ishiwatari, R., and M. Uzaki. "Diagenetic Changes of Lignin Compounds in a More Than 0.6 Million-Year-Old Lacustrine Sediment (Lake Biwa, Japan)." Geochimica Et Cosmochimica Acta 51, no. 2 (Feb 1987): 321-28.〕 Further, they can distinguish between different land-based plants, depending on the type of photosynthesis they undergo. Therefore, the C/N ratio serves as a tool for understanding the sources of sedimentary organic matter, which can lead to information about the ecology, climate, and ocean circulation at different times in Earth’s history.〔Ishiwatari, R., and M. Uzaki. "Diagenetic Changes of Lignin Compounds in a More Than 0.6 Million-Year-Old Lacustrine Sediment (Lake Biwa, Japan)." Geochimica Et Cosmochimica Acta 51, no. 2 (Feb 1987): 321-28.〕
C/N ratios in the range 4-10:1 are usually from marine sources, whereas higher ratios are likely to come from a terrestrial source.〔Gray KR, Biddlestone AJ. 1973. Composting - process parameters. The Chemical Engineer. Feb. pp 71-76〕 〔Stewart, Keith (2006). It's A Long Road to A Tomato. New York: Marlowe & Company. p. 155. ISBN 978-1-56924-330-5.〕 Vascular plants from terrestrial sources tend to have C/N ratios greater than 20. 〔Ishiwatari, R., and M. Uzaki. "Diagenetic Changes of Lignin Compounds in a More Than 0.6 Million-Year-Old Lacustrine Sediment (Lake Biwa, Japan)." Geochimica Et Cosmochimica Acta 51, no. 2 (Feb 1987): 321-28.〕 〔Prahl, F. G., J. R. Ertel, M. A. Goni, M. A. Sparrow, and B. Eversmeyer. "Terrestrial Organic-Carbon Contributions to Sediments on the Washington Margin." Geochimica Et Cosmochimica Acta 58, no. 14 (Jul 1994): 3035-48.〕 The lack of cellulose, which has a chemical formula of (C6H10O5)n, and greater amount of proteins in algae versus vascular plants causes this significant difference in the C/N ratio. 〔Ishiwatari, R., and M. Uzaki. "Diagenetic Changes of Lignin Compounds in a More Than 0.6 Million-Year-Old Lacustrine Sediment (Lake Biwa, Japan)." Geochimica Et Cosmochimica Acta 51, no. 2 (Feb 1987): 321-28.〕 〔Meyers, Philip A., and Heidi Doose. "29. SOURCES, PRESERVATION, AND THERMAL MATURITY OF ORGANIC MATTER IN PLIOCENE–PLEISTOCENE ORGANIC-CARBON–RICH SEDIMENTS OF THE WESTERN MEDITERRANEAN SEA." Proceedings of the Ocean Drilling Program: Scientific results. Vol. 161. The Program, 1999.〕 〔Müller, P. J. "CN ratios in Pacific deep-sea sediments: Effect of inorganic ammonium and organic nitrogen compounds sorbed by clays." Geochimica et Cosmochimica Acta 41, no. 6 (1977): 765-776.〕
When composting, microbial activity utilizes a C/N ratio of 30-35:1 and a higher ratio will result in slower composting rates.〔Prahl, F. G., J. R. Ertel, M. A. Goni, M. A. Sparrow, and B. Eversmeyer. "Terrestrial Organic-Carbon Contributions to Sediments on the Washington Margin." Geochimica Et Cosmochimica Acta 58, no. 14 (Jul 1994): 3035-48.〕 However, this assumes that carbon is completely consumed, which is often not the case. Thus, for practical agricultural purposes, a compost should have an initial C/N ratio of 20-30:1.〔Dahlem. "Flux to the Seafloor", Group Report, eds. K.W. Bruland et al., pp. 210–213, 1988.〕
Example of devices that can be used to measure this ratio are the CHN analyzer and the continuous-flow isotope ratio mass spectrometer (CF-IRMS). 〔Brenna, J. Thomas, et al. "High‐precision continuous‐flow isotope ratio mass spectrometry." Mass spectrometry reviews 16.5 (1997): 227-258.〕 However, for more practical applications, desired C/N ratios can be achieved by blending common used substrates of known C/N content, which are readily available and easy to use.
== Applications ==
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