Study of free and occluded particulate organic matter in soils by solid state 13C CP-MAS NMR spectroscopy and scanning electron microscopy

• Published in: Australian journal of soil research Vol. 32; no. 2
• Main Authors: Golchin, A, Oades, J.M, Clarke, P. (Adelaide Univ., Glen Osmond (Australia). Dept. of Soil Science), Skjemstad, J.O. (Commonwealth Scientific and Industrial Research Organisation, Glen Osmond (Australia). Div. of Soils)
• Format: Journal Article
• Language: English
• Published: 1994
• Subjects: ANALISIS DEL SUELO; ANALYSE DE SOL; CARACT MICROMORFOLOGICAS DEL SUELO; CHIMIE DU SOL; DENSIDAD DEL SUELO; DENSITE DU SOL; MATERIA ORGANICA; MATIERE ORGANIQUE; QUIMICA DEL SUELO; SOL; SUELO; TRAIT MICROMORPHOLOGIQUE DU SOL
• ISSN: 0004-9573; 1446-568X
• DOI: 10.1071/sr9940285

A simple densimetric method for the separation of free and occluded particulate organic materials was developed and applied to 5 virgin soils. The chemical composition of occluded and free organic materials was investigated by solid-state 13C CP-MAS NMR spectroscopy. Despite the differences in soils, environmental conditions and vegetation, the organic structure of the free light fraction was similar in 4 of the 5 soils. This fraction consisted of 55-63 percent O-alkyl C, 18-25 percent alkyl C, 14-18 percent aromatic C, and 5-7 percent carbonyl C. In the other soil, this fraction showed a higher proportion associated with organic materials contained in the occluded light fraction. It is considered that the occluded organic matter is an old pool of carbon that has been accreted within aggregates during decades of root growth and it is that pool which is lost due to cultivation.