X‐ray Technique to Evaluate Pedon and Erosion Variability of an Ava Map Unit

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AbstractAn uneroded map unit of Ava soil was examined to determine the presence of and variability in depth to the upper and lower boundaries of the argillic horizon, the second parent material, the horizon of maximum x‐ray mass absorption coefficient, the fragipan, the A and E horizons, and the clay maximum prior to accelerated erosion. Twelve pedons from six pits were examined to address the depth variability of selected soil features. These features have often been used as reference markers to provide a basis from which to estimate the soil loss from erosion. Considering all sampled pedons in an Ava map unit on a ridgetop, all selected soil parameter boundaries but the depth to the upper boundary of the fragipan were found to be reliable reference markers. The mean depth to the lower boundary of the horizon with the maximum coefficient of x‐ray mass absorption coincided with the mean depths to the lower boundary of the clay maximum, Fe maximum, and top of the second parent material, but did not coincide with the mean depth to the lower boundary of the argillic horizon. Iron content and x‐ray mass absorption coefficient were highly correlated because elements with high mass, such as Fe, increase the x‐ray mass absorption coefficient in a horizon. Where accelerated erosion occurred on a landscape segment, the lower boundary of the horizon of maximum x‐ray mass absorption coefficient, as well as other lower boundaries of subsoil parameters, could be used as reference markers to provide a basis for estimating soil loss from erosion.