Studying the Physical Protection of Soil Carbon with Quantitative Infrared Spectroscopy. Issue 3 (June 2016)

• Record Type: Journal Article
• Authors: Barthès, Bernard G.; Kouakoua, Ernest; Moulin, Patricia; Hmaidi, Kaouther; Gallali, Tahar; Clairotte, Michaël; Bernoux, Martial; Bourdon, Emmanuel; Toucet, Joële; Chevallier, Tiphaine
• Is Part Of: Journal of near infrared spectroscopy. Volume 24:Issue 3(2016)
• Page Start: 199
• Page End: 214
• Publication Date: 2016-06
• Subjects: soil organic matter -- soil respiration -- carbon sequestration -- carbonates -- near infrared reflectance spectroscopy -- mid-infrared reflectance spectroscopy; Near infrared spectroscopy -- Periodicals; 543.5
• DOI: 10.1255/jnirs.1232
• Languages: English
• ISSNs: 0967-0335

Abstract

Near infrared (NIR) and mid-infrared (mid-IR) reflectance spectroscopy are time- and cost-effective tools for characterising soil organic carbon (SOC). Here they were used for quantifying (i) carbon (C) dioxide (CO2 ) emission from soil samples crushed to 2 mm and 0.2 mm, at 18°C and 28°C; (ii) physical C protection, calculated as the difference between CO2 emissions from 0.2 mm and 2 mm crushed soil at a given temperature; and (iii) the temperature vulnerability of this protection, calculated as the difference between C protection at 18°C and 28°C. This was done for 97 topsoil samples from Tunisia, mostly calcareous, which were incubated for 21 days. Soil CO2 emission increased with temperature and fine crushing. However, C protection in 0.2–2 mm aggregates had little effect on the temperature vulnerability of CO2 emission, possibly due to preferential SOC protection in smaller aggregates. In general, NIR spectroscopy, and to a lesser extent mid-IR spectroscopy, yielded accurate predictions of soil CO2 emission (0.60 ≤ R 2 ≤ 0.91), and acceptable predictions of C protection at the beginning of incubation (0.52 ≤ R 2 ≤ 0.81) but not over the whole 21 day period ( R 2 ≤ 0.59). For CO2 emission, prediction error was the same order of magnitude as, and sometimes similar to, the uncertainty of conventional determination, indicating that a noticeable proportion of the former could be attributed to the latter. The temperature vulnerability of C protection could not be modelled correctly ( R 2 ≤ 0.11), due to error propagation. The prediction of SOC was better with NIR spectroscopy and that of soil inorganic C (SIC) was very accurate ( R 2 ≥ 0.94), especially with mid-IR spectroscopy. Soil CO2 emission, C protection and its vulnerability were best predicted with NIR spectra, those of 0.2 mm samples especially. Mid-IR spectroscopy of 2 mm samples yielded the worst predictions in general. NIR spectroscopy prediction models suggested that CO2 emission and C protection depended (i) on aliphatic compounds (i.e. labile substrates), dominantly at 18°C; (ii) on amides or proteins (i.e. microbial biomass), markedly at 28°C; and (iii) negatively, on organohalogens and aromatic amines (i.e. pesticides). Models using mid-IR spectra showed a negative influence of carbonates on CO2 emission, suggesting they did not contribute to soil CO2 emission and might form during incubation. They also suggested that CO2 emission and C protection related to carboxylic acids, saturated aliphatic ones especially.