Soil geomorphic, hydrologic, and sedimentologic relationships and evaluation of soil survey data for a Mollisol catena on the Des Moines Lobe, central Iowa

摘要

Defining interactions between agriculture and the environment requires detailed information from several disciplines. This study developed a generalized model linking soil-geomorphology, soil moisture regime, parent material stratigraphy, and hydrology for the Clarion-Nicollet-Webster catena in central Iowa and quantified the capability of soil survey data to evaluate landscapes. Detailed soil and geomorphic maps and stratigraphic and hydrologic cross-sections were constructed from hydraulic head data and characterization data of 128 cores collected at the study site. Two strata of surficial sediments overlying glacial till were identified at lower landscape positions. Morphologic and stratigraphic evidence suggested a postglacial colluvial/alluvial origin for the deposits. Slowly permeable glacial till promoted development of a shallow circulating groundwater system in overlying sediments and jointed glacial till. The water table usually mirrored the landsurface, resulting in groundwater flow directed toward swales;Distribution of soils on upper landscape positions was related to hillslope geomorphology and textural differences in glacial till parent material. Poorly drained soils in swales were generally not related to buried geomorphic surfaces. Lateral groundwater flow influenced the genesis of calcareous Aquolls in swale centers surrounded by noncalcareous and often deeply leached Aquolls near the base of hillslopes. Water table fluctuation and soil morphology relationships suggested some soils contain relict features related to longer saturation prior to artificial drainage;Map unit composition of the county soil survey was estimated by GIS overlay analysis with the detailed soil map and ranged from 0 to 58% of the named series or taxadjunct. The largest factor determining map unit variability was misinterpretation of the low contrast tonal pattern on the county survey photo base map. Map unit interpretive purity, however, was very high. Average expected yield interpretations were identical for both scale maps and agreed reasonably well with measured yields. These results suggested county soil survey data are acceptable to quantitatively evaluate landscapes; however, the map unit variability necessitates on-site investigation for intensive land uses.