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Soil Organic Matter Testing and Labile Carbon Identification by Carbonaceous Resin Capsules
Author(s) -
Johns Mitchell M.,
Skogley Earl O.
Publication year - 1994
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/sssaj1994.03615995005800030016x
Subject(s) - chemistry , soil water , organic matter , adsorption , atomic absorption spectroscopy , environmental chemistry , soil organic matter , nuclear chemistry , organic chemistry , physics , environmental science , quantum mechanics , soil science
An alternative test for soil organic matter that does not produce toxic dichromate waste, as does the Walkley‐Black test, and that also allows identification of labile soil C components is currently desired. The objectives of this study were to apply carbonaceous resin capsules for measurement of soil organic C (SOC) and for identification of soluble SOC constituents. Seven carbonaceous resins, selective for nonpolar organic adsorbates, were evaluated. The resins were tightly packed as spherical capsules and placed in saturated soil pastes of 19 Montana soils. Resin capsules were desorbed with NaOH, CH 3 OH, CHCl 3 , and C 6 H 14 . Capsules extracted with the organic solvents were used in identification by nuclear magnetic resonance and infrared spectroscopy. Ultrafiltration and atomic absorption spectrophotometry of trace metals were also used. All resin capsules sorbed measurable levels of soil labile C (LC). All the resin types provided statistically significant prediction of SOC. The Ambersorb 564 resin showed the highest prediction, with a linear relationship between capsule‐extracted LC (NaOH) and SOC of r 2 = 0.09 ( P < 0.0001). Prediction results from these soils suggested a linear relationship between soluble SOC and solid‐phase SOC, describable as constant partitioning. Labile C was composed of mostly aliphatics and some aromatics. Carbohydrates, OH, COOH groups, and metal‐organic complexes were present. Most of the LC was composed of low molecular weight humics (<1000 daltons). The ability of LC to be desorbed by the more nonpolar solvents indicated an amphipathic character for some LC constituents. The resin capsule methodology showed good testing potential for these SOC investigations.