Structural Features of Soil Humic Acids as Assessed by ~(13) C Nuclear Magnetic Resonance and Analytical Pyrolysis in Areas under Coffee Cultivation in Southeastern Brazil

摘要

Agroforestry systems (AGFs) have been shown to enhance soil organic matter (SOM) levels when compared to monoculture agricultural systems [1]. Nevertheless, information on the chemical and structural characterization of SOM in areas under agroforestry remains scarce. There has been a great deal of interest in the utilisation of more specific and accurate techniques for characterizing the chemical nature of SOM. Studies have shown that combining the techniques~(13)C nuclear magnetic resonance with cross-polarization magic angle spinning (~(13)C CP-MAS/NMR) and analytical pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) is a valuable tool for structural studies on humic substances [3, 5]. The constant input and quality of organic residues derived from tree-component in AGFs, in contrast to monoculture systems (full sun coffee), is expected to have an important effect on the humification processes and consequently on the chemical and structural features of soil humic substances. Our objective was to identify the qualitative changes of soil humic acids as influenced by management (agroforestry coffee versus full sun coffee) in areas under coffee production in the Atlantic Coastal Rainforest domain in the state of Minas Gerais, Brazil.