Suitability of the anthrone–sulfuric acid reagent for determining water soluble carbohydrates in soil water extracts


The anthrone–sulfuric acid method of quantifying soil carbohydrates is commonly used but reportedly subject to interference from ions found in soil solution. A subset of the samples generated from a study on soil amendments (compost plus manure versus fertilizer) and crop rotations (oats and green manure grown in alternate years with potato) was used to study the effect of soil solution ionic composition on carbohydrate recovery using the anthrone–sulfuric acid method. Soils were incubated for 24 h at 85°C using a soil-to-water ratio of 1:10 (w:v). After filtration, dilution and addition of the anthrone–sulfuric acid reagent, absorbance was read at 625 nm. Ionic composition of the soil-water extracts was determined using inductively coupled plasma spectrometry and ion chromatography. Fractional recoveries of 10 μg glucose ml−1 added to the extracts ranged from 0.56 to 1.03 and averaged 0.92, 0.78, 1.0, 0.93 and 0.90 for the five dates sampled. No significant correlations were found between spike recovery and amounts of NO3−, Fe, Mn, or Cl−. In a separate experiment, simulated soil extracts prepared from salts demonstrated no significant effect of solution composition on glucose recovery at either 10 or 30 μg glucose ml−1 added as a spike. These results suggest that systematic ion interference was unlikely to have occurred in the experiment and that glucose recovery was high and consistent across treatments. Some anomalous results suggest, however, that careful controls, such as spike recovery experiments and meticulous analytical procedures, must be employed in order to obtain reliable results.


Soil Biogeochemistry and Microbial Ecology

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Soil Biology and Biochemistry



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