A Simple Colorimetric Measurement for Humic Acids in Spodic Horizons

Abstract

Abstract An organic buffer, 2‐amino‐2‐methyl propanol neutralized to pH 10 with 4 M acetic acid, was investigated as an extractant for soil organic matter. The color of the humic acid fraction of this extract proved to be a distinctive marker of spodic horizon organic matter. Both the humic acid and fulvic acid fractions were quantified by a simple comparator used to classify color in natural waters. The fulvic acid color was functionally related to aluminum in the extract and also to aluminum in the pyrophosphate extract. If the extract contained iron, it was associated with the humic acid color, although humic acid color could be present without iron. The humic acid color was present only in those soils with pH < 4.5. Data are presented to demonstrate the ruggedness of the procedure with respect to variations of extraction time and of the soil/solution ratio.