Semi-quantitative analysis of FT-IR spectra of humic fractions of nine US soils

Authors: He, Zhongqi; Honeycutt, Charles

Submitted to: International Humic Substances Society Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2009
Publication Date: 3/18/2009
Citation: He, Z., Honeycutt, C.W. 2009. Semi-quantitative analysis of FT-IR spectra of humic fractions of nine US soils. International Humic Substances Society Conference. page 43.

Interpretive Summary:

Technical Abstract: Fourier Transform Infrared Spectroscopy (FT-IR) is a simple and fast tool for characterizing soil organic matter. However, most FT-IR spectra are only analyzed qualitatively. In this work, we prepared mobile humic acid (MHA) and recalcitrant calcium humate (CaHA) from nine soils collected from six states in the USA. FT-IR spectra of these humic fractions were obtained. Three absorption bands of these FT-IR spectra were quantified by both absorption heights and areas. Band A from 3020-2800 cm-1 represented C-H absorption from methyl and ethylene groups. Band B from 1740-1700 cm-1 and 1640-1600 cm-1 represented C=O bands of amide and carboxylic acid or ketone groups. Band C at approximately 1081 cm-1 was used as an internal reference to facilitate semi-quantitative analysis from the ratios of A/C and B/C. Absorption band height and absorption area were highly correlated, with a correlation coefficient of 0.986, even though the ratios of A/C and B/C were always greater for band height than band area. For band height, the A/C ratio ranged from 1.16 to 0.08, and the B/C ratio ranged from 6.40 to 0.86. The A/C ratio was positively correlated with B/C ratio for a given humic fraction (MHA or CaHA). This research provides basic information for further investigating differences in organic matter composition change among different soils and management practices.