Spectroscopic and Thermal Assessment of Organic Matter in Iowa Mollisols.

Both the concentrations and the stocks of soil organic carbon vary across the landscape. Do the amounts of various components of SOM vary with landscape position?

We studied four soils in central Iowa, two developed in till and two developed in loess. There were well-drained and poorly drained soils. We collected surface-horizon samples and fractionated the organic matter from the entire soil samples as well as from the clay fractions. We treated these samples with four 10% HF treatments to dissolve minerals.

We used both diffuse reflectance Fourier-transform infrared spectroscopy (DFIRT) and thermal analysis to assess the organic matter in these soils.

Differential thermogravimetry is a promising approach to obtain a simple, semi-quantitative estimate of the recalcitrant fraction of soil organic matter.

DRIFT spectra are challenging to interpret, but quantitative goodness-of-fit comparisons of simulated composites with real spectra may permit better interpretations and at least semi-quantitative evaluations. Here we explore the potential of using spectral decomposition and linear combination fitting to assessing the contribution of organic components in soil organic matter such as lignin residues, amino acid residues, carbohydrate residues, and cutin residues.