Moisture Characteristics of Pennsylvania Soils: III. Parent Material and Drainage Relationships

Abstract

Available moisture (WA), assumed as the difference between moisture contents of ‘undisturbed cores’ equilibrated at ⅓ atm of tension and of < 2-mm sieved samples equilibrate at 15 atm of tension and expressed on a volume basis, was determined on horizons collected from 207 profiles in 27 Pennsylvania counties. Weighted means of WA, coarse fragments, sand, silt, and clay were calculated for A, B, and C horizons and for 0–30, 30–60, 60–90, and 90–120-cm depth increments for each soil profile, and the profiles grouped according to parent material and drainage class. Parent material groups showed the following relative amounts of cumulative WA: aeolian > alluvium > limestone > till > shale > sandstone > glacial-fluvial. Differences in WA are related to textural relationships and coarse fragment contents, with WA decreasing with increasing amounts of clay, sand, and coarse fragments. WA generally decreased with increasing depth within each parent material group with the relative amounts of WA within horizons as follows: A > B > C. Within a parent material group, content of coarse fragments was the most important factor determining WA content within the soil profiles. Cumulative WA also tended to increase as soils became more poorly drained and decreased with depth within each drainage class. Differences in the drainage were usually related to the parent material from which the soil developed. Therefore, differences in parent material should be the primary consideration when estimating WA and the effect of drainage conditions upon WA should only be considered when these differences occur within a parent material group.