Abstract
Organic matter (OM) is a key component of soils but information on its chemistry and behavior in soils is still incomplete. Numerous methods are commonly used to characterize and monitor OM dynamics, but only a few include the qualities required to become routine techniques i.e. simple, rapid, accurate and at low cost. Rock–Eval pyrolysis (RE pyrolysis) is a good candidate, as it provides an overview of OM properties by monitoring four components related to the main major classes of organic constituents (from A1 for the labile biological constituents to A4 for the mature refractory fraction). However, a question is still pending: do these four major classes used in the literature reflect a pertinent compositional chemical counterpart? 13C Nuclear Magnetic Resonance Spectroscopy in the solid state (13C CPMAS NMR) has been used to answer this question by collecting information on structural and conformational characteristics of OM. Moreover, in order to avoid the blurring effect of pedogenesis on OM dynamics, a “less complex OM” source, i.e. compost samples, has been used. Results showed significant and high determination coefficients between classes, indices (of transformation of plant biopolymers, humification…) from RE pyrolysis, and the main classes of OM characterized by 13C NMR, e.g. A1 & A2 with labile/easily degradable components (alkyl C et O-alkyl C), A3 & A4 with humified OM (with aromatic C and phenolic C). The R index (contribution of bio-macromolecules) is correlated with phenolic and aromatic C, whereas the I index (related to immature OM) refers to labile––easily degradable components (alkyl C et O-alkyl C). The results confirm the pertinence of RE pyrolysis to monitor OM dynamics.
Highlights
Soil organic matter (SOM) benefits of a positive perception since a long time
This study focuses on RE pyrolysis as a method to evaluate both the nature and behavior of natural organic matter (OM)
In a first step to explore the pertinence of RE pyrolysis for SOM, compost excludes the complex ‘‘interferences’’ due to pedogenetic processes occurring in soils
Summary
Soil organic matter (SOM) benefits of a positive perception since a long time. It is clearly associated with the concept of soil fertility and, more recently, of soil quality., a minor component of soil in quantitative terms, organic matter influences many soil properties, which in turn affects several soil functions: for example, it provides nutrient reservoirs, it is a substrate for microbial activity, it preserves the environment, and it is critical for sustaining and increasing agricultural productivity (Schnitzer 2005). Very few are used routinely, because of the common need for preliminary sample preparation (e.g. extraction or purification), or due to their complexity and cost (e.g. NMR techniques). Rock–Eval pyrolysis (RE pyrolysis; Disnar et al 2003; Sebag et al 2006) or Near-Infrared Spectroscopy (NIRS; Albrecht et al 2008a; 2009) constitute two potential candidates for routine techniques
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