Field Identification of Spodic Horizons with Potassium Hydroxide Extractable Aluminum and Humic Acid Color1
- G. G. S. Holmgren and
- R. D. Yeck2
Fifty-nine previously classified soils were analyzed for humic acid color and KOH aluminum. These variables were used to develop alternate criteria for the spodic horizon by comparing data with the existing classifications. The resulting criteria are as follows: Humic acid color greater than or equal to 10 L platinum color units per gram or, maximum B horizon KOH-extractable Al > 7 g kg−1 (0.7%), with a ratio of maximum Al in the B horizon to minimum Al in the E horizon of 2 or more. This latter requirement is necessary to distinguish Spododols from Andepts if the KOH aluminum criterion is used. Soils with discrepant classifications by laboratory data, field morphology, and by these alternate criteria were examined to bring out the reasons for the differences. A second set of soils was then examined in terms of the proposed criteria. Of this second set, 88% were classified by the proposed criteria in agreement with either the laboratory or the field estimate of the classification. The principal disagreements in both sets of soils could be explained as a consequence of the questionable exclusion from Spodosols of soils with low pyrophosphate (Fe + Al)/dithionite (Fe + Al) ratios and by the effect of high or low clay contents on the pyrophosphate (Fe + Al)/clay ratio requirement. In some cases, the classification more closely corresponds to the field morphology than does classification by the existing laboratory criteria. A principal advantage is that the procedures can be performed under field conditions.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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