The influence of elevation on the humic-fulvic acid ratio in soils of the Santa Catalina Mountains, Pima County, Arizona

Abstract

An elevational study of organic matter components was made of shallow soils of the Santa Catalina Mountains, Pima county, Arizona. At nineteen elevations (900 to 2700 m), total carbon, extractable organic carbon, humin carbon (tightly bound organic carbon), humic acid carbon, fulvic acid carbon, humic-fulvic acid ratios and E4/E6 ratios were determined. Parameters except the humic-fulvic acid ratios showed high correlations, R² at least .78, with elevation. Of these only the E4/E6 ratio was negatively correlated with elevation. Uncorrelated humic-fulvic acid ratios indicate no proprotional trend of the relative proportions of humic and fulvic acids. The E4/E6 ratio decrease with elevation agreed with all parameters. Humic acids are older, larger and contain higher concentrations of aromatics with increasing elevation. The humic-fulvic acid ratio, based on classical organic matter separation, does not produce a discriptively useful means for a range of climatically different soils. The E4/E6 ratio is more useful in evaluating soil genesis via composition.