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Investigating the Chemical Characteristics of Soil Organic Matter Fractions Suitable for Modeling
Author(s) -
Sohi Saran P.,
Mahieu Nathalie,
Powlson David S.,
Madari Beatá,
Smittenberg Rienk H.,
Gaunt John L.
Publication year - 2005
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2004.0262
Subject(s) - organic matter , soil organic matter , soil water , decomposition , chemistry , reactivity (psychology) , fraction (chemistry) , nutrient , composition (language) , manure , aggregate (composite) , environmental chemistry , soil science , mineralogy , geology , agronomy , materials science , organic chemistry , biology , medicine , linguistics , philosophy , alternative medicine , pathology , composite material
Current models of soil organic matter (SOM) turnover tend to invoke pools that are defined by their contrasting first‐order reactivity constants but which cannot be directly measured. New models may be based around fractions defined by procedures that can be used to isolate them experimentally. The drawback of such fractions is that they may display properties that are not sufficiently distinct or which vary in time or space. In this study the properties of two fractions from soils of contrasting geographical origin and under different nutrient management were examined using 13 C nuclear magnetic resonance (NMR) spectroscopy. The fractions were free SOM (FR‐SOM, discrete organic particles located between stable aggregates), and intra‐aggregate SOM (IA‐SOM, discrete organic particles within stable aggregates). The composition of both fractions was highly consistent across soil types and environments, but the fractions differed significantly in the proportion of C present in five of the seven functional C groups identified by NMR ( P < 0.05). The results confirmed that IA‐SOM contains a greater proportion of microbial products and more resistant C as compared with the FR‐SOM. Nutrient management affected fraction composition in four functional groups most abundant in plant material or farmyard manure ( P < 0.05). The effects were considerably less pronounced when the analysis was restricted to plots receiving inorganic (or zero) N. Overall the results supported the view that free and intra‐aggregate organic matter occupy contrasting positions in the decomposition sequence, and are likely to display reactivities sufficiently distinct to operate as discrete pools in new SOM models.