Assessing Bt
Horizon Character in Sandy Soils
Using
Ground-Penetrating Radar:
Implications
for Soil Survey
D.
L. Mokma, R. J.
Schaetzl, E. P. Johnson and J. A. Doolittle
In sandy soils, the cumulative
thickness of lamellae (textural bands) is the primary criterion used for the
determination of an argillic horizon (Soil Survey Staff, 1975; Miles and
Franzmeier, 1981). Such soils present
challenges in mapping because (i) the presence of absence of this diagnostic
horizon is not reflected at the soil surface and (ii) Psammentic Hapludalfs and
Alfic Udipsamments, sandy soils whose classifications depend on thickness of
lamellae, occur in both consociations and complexes with each other. Productivity is affected by the cumulative
thickness of and depth to the lamellae, in part because these bands markedly
increase water-holding capacities of sandy soils. To optimize production and increase land-use efficiency, land
owners often need to know which soils is dominant in a field.
In other sandy soils, finer
materials, rather than lamellae, may occur in the subsoil. Although some measure of the mean depth to
these fine materials can be accomplished by point data, variability in depth
is difficult to determine from the limited number of auger observations usually
made during soil mapping. As in soils
with lamellae, thickness of the sand over finer material greatly influences
productivity. (Warncke et al., 1985).
Ground-penetrating radar (GPR) is a field technique that has been used successfully to study organic soil thickness (Shih and Doolittle, 1984; Collins et al., 1986), depth to bedrock in mineral soils (Olson and Doolittle, 1985; Doolittle et al., 1988), depth to and lateral extent of argillic horizons (Collins and Doolittle, 1987; Truman et al., 1988) and to update soil surveys (Schellentrager et al., 1988). The GPR may have potential in gathering data to assist soil scientists in mapping the sandy soils described above. The objectives of this study were to determine the usefulness of GPR for assessing the character and depth of Bt horizons in sandy soils and to estimate map unit composition.