Saturday, 15 July 2006

Geochemistry in Soil Survey and Soil-Landscape Analysis.

M.A. Wilson, R. Burt, S.J. Indorante, A.B. Jenkins, and J.V. Chiaretti. USDA-NRCS, 100 Centennial Mall N, MS 41, Lincoln, NE 68508

The process of mapping and classifying soils can provide a foundation for the systematic evaluation of soil geochemistry on a local and regional basis. The development and use of soil-landscape models complemented by laboratory and morphological data during the mapping of soils allows us to locate sites or pedons that represent the dominant soil component on each landscape unit and, in turn, define soil series in terms of their catena. These representative pedons have been the basis of soil survey sampling and laboratory characterization for many years and are an ideal choice for analysis of soil geochemistry. The NRCS Soil Survey Laboratory has been producing geochemical data on selected soils for a number of years with analyses produced on all or selected horizons. This analytical approach associates geochemistry data, generated to depths up to 2 m or lithic contact, with soil morphology, location, and landscape information, plus a full range of other laboratory analyses. On-going research is also addressing elemental variability within named mapping units and the extent of elemental segregation by pedogenic processes in landscapes. These geochemistry data have multifaceted applications within soil survey. Data may be useful for defining soils or mapping units, such as defining ranges of properties, taxonomic placement, or the naming of soil series. Geochemistry has also been used in characterizing pedon and landscape processes (e.g., direction or extent of weathering) and determining parent material origins. Geochemistry adds strong interpretative value to soil surveys by providing substance to soil quality, land-use planning, geologic baseline data, ecological evaluation, crop and forage suitability, plus more importantly health issues relating to humans and livestock. Environmental protection is a growing concern, with requirements to monitor waste management practices, and evaluate the possibility, degree, source, or risk of contamination. With an appropriate dataset, scientists in the National Cooperative Soil Survey Program can provide the public with an understanding of trace element ranges for different soils, parent materials, or regions; and assist in interpreting these data based on pedogenic processes. Soil scientists can help users of our soil information understand landscape distribution of soils, processes in soils that lead to elemental distribution, and degree of variability in soil properties that occur in a landscape. Geochemistry data on soil landscapes support our soil survey interpretations and foster knowledgeable decisions on landuse issues.

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