TA-SOM: Characterization of soil organic matter using thermal analysis
Characterization of soil organic matter quality using thermal analysis technology
National Institute for Food and Agriculture, United States Department of Agriculture, Award #2010-65107-20351
The organic matter content of soil represents the balance between fresh plant, animal and microbial inputs, and losses due to microbial mineralization (resulting in CO2 emissions) and erosion. Soil organic matter is the largest active terrestrial pool of carbon, and the balance of carbon into or out of soils plays an important role in global climate change. Increasing carbon stocks in soil is an important opportunity to mitigate climate change, but researchers have argued that organic matter quality must be better quantified to avoid sequestering decomposable rather than stable carbon. Studies have also shown that current soil carbon stocks are vulnerable to disturbance and climate change, thus requiring an assessment of how quality may affect vulnerability. Soil organic matter consists of everything from easily decomposable microbial and root exudates that persist only for days, to mineral-bound and chemically complex materials that persist for centuries or millennia. This range in decomposability is referred to as the ?soil organic matter quality continuum?. The conventional approach is to separate more or less decomposable pools using various biological, chemical, and physical fractionation methods, or modeling using multiple compartments. Because soil organic matter is a continuum rather than a series of discrete pools, any laboratory fractionation used to quantify organic matter quality will not be completely satisfactory. The demand for an integrative means of assessing organic matter quality, therefore, remains high. Recent experiments provide strong evidence that thermal analysis technology is a promising tool to characterize organic matter quality. Thermal analysis involves the controlled heating of a small sample of soil, and measuring the resulting mass loss and energy flow. The objectives of this research are to: quantify the thermal behavior of soil organic matter components; develop quantitative expressions of thermal data; test for organic matter quality differences in soil samples; and build a public database of thermal analysis results. The experimental approach consists of sampling a number of long-term field experiments with presumed differences in organic matter quality, thermal analysis of samples, and comparing results to conventional methods. Three approaches to linking organic matter quality to thermal data will be tested: curve subtraction, thermal indices, and peak deconvolution. This research represents an important opportunity to develop a quantitative means of evaluating the entire continuum of soil organic matter quality. A thermal analysis approach will alleviate much of the need for time-consuming biological assays of quality because thermal analyses can be produced in a matter of hours, rather than weeks or months. The development of quantitative indices of thermal stability that can be linked to conventional means would be a significant advance in our fundamental understanding of the nature and dynamics of soil organic matter, as well as a state-of-the-art tool with potential widespread applicability to soil quality assessments for agricultural, rangeland and forest productivity.