FT-IR Spectroscopy of Organic Matter in Tropical Soils: Changes Induced through Deforestation

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Abstract
This article describes a series of transmission Fourier transform infrared (FT-IR) spectroscopy measurements of soil layers, especially organic soil layers, originating from a tropical forest and from a pasture, which was developed after deforestation of the tropical soil in 1987. Spectral information obtained from forest and pasture soil layers from central Rondônia, Brazil, was analyzed and compared. A variety of bands characteristic of molecular structures and functional groups have been identified for these complex samples. Cluster analysis revealed that such land use change affects the spectroscopic behavior of the organic soil layers. A significantly closer relationship between the pasture soil layers in comparison to the forest soil layers was obtained. This result indicates a higher homogeneity of the intoduced litter from pasture vegetation compared to forest. The application of regression models enabled the estimation of soil parameters, such as organic carbon and nitrogen; the identification and differentiation of organic forest soil horizons; and the determination of the decomposition status of soil organic matter in distinct layers. On the basis of the data presented in this study, it may be concluded that FT-IR spectroscopy is a powerful tool for the investigation of decomposition dynamics and litter quality in tropical soils.