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


Principal Investigator

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.

AfDE: Soil organic matter characterization in African Dark Earths

Discrete patches of tropical, anthropogenic Dark Earths contain approximately three times the amount of carbon as adjacent soils due to long-term human inputs of organic and pyrogenic materials. Tropical Dark Earth soils are globally widespread and have been found in Amazonia, Australia and tropical West Africa, but they represent a small proportion of total area. In Ghana and Liberia, African Dark Earths (AfDE) contain substantial amounts of black carbon (BC) from charred human waste, which contribute to stable soil carbon. At the same time, AfDE is substantially more fertile and productive compared to adjacent soils. How inputs to AfDE simultaneously enhance organic C cycling and storage is not well understood. The goal of this study is to characterize soil organic matter in AfDE and contrasting adjacent soils to ascertain mechanisms that enable concurrent C cycling and C storage.

PAS: Pennsylvania Anthracite Soils

An important legacy of past coal mining in central Pennsylvania, is a massive amount of anthracite coal fines/spoils that were eroded and transported into the Schuylkill and Susquehanna Rivers. This anthracite coal has accumulated in thick deposits in riparian soils. This collaborative project seeks to determine the extent of these soils (e.g., Gibraltar series), and to quantify and characterize the organic carbon in soil profiles to determine the contribution of coal to total soil carbon.