Use of Pyrolysis GC/MS for Assessing Changes in Soil Organic Matter Quality

Abstract

There is a need for rapid methods of assessing changes in the quality of agricultural soils because of the need to monitor such changes under different land management practices. For example, the increasing interest in use of agricultural lands for application of coal combustion byproducts, such as fluidized bed ash, has led to concern that such use may be detrimental to the quality of soil organic matter. Pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) techniques hold promise as rapid procedures for detecting changes in the organic matter composition of soils, which contrasts with the often laborious chemical methods used commonly for analyzing soil organic matter. To evaluate Py-GC/MS for this use, we characterized changes in the organic matter composition of bed ash-amended soils by both chemical and pyrolytic analyses. The chemical analysis of the soil samples had shown substantial degradation and loss of organic matter as a result of the ash amendments, and the pyrolytic analyses reflected these losses of soil organic matter by decreases in the total peak areas within the total ion chromatogram. Information on the changes in composition of soil organic matter was reflected by changes in peak area for individual pyrolytic products, and the identity of more than 40 pyrolytic products was determined from their mass spectral data. This permitted identification of various pyrolytic signature products for the protein, carbohydrate, and humic fractions of soil organic matter. The change in peak areas of these different signature products could be correlated with changes in the content of different constituents in the soil organic matter as measured by chemical analysis. The pyrolysis product furfural was correlated with changes in carbohydrate content. Changes in production of 2-methoxyphenol, guaiacol, vinylphenol, vinylguaiacol, and isoeugenol represented changes within the humic fraction. Nitrile and propane pyrolysis products were correlated with changes in protein content. The good agreement between classical chemical analysis and pyrolytic analysis indicates that Py-GC/MS can be used to monitor changes in the organic matter composition of agricultural soils subjected to environmental stress.