Soil Properties and Classification (Soil Taxonomy)
The consistent use of standard procedures is one of the strengths of the National Cooperative Soil Survey in the USA. Together these standards ensure that soil descriptions and data can be compared, grouped, classified, and interpreted effectively. Import
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Soil Properties and Classification (Soil Taxonomy) Craig A. Ditzler
3.1
Documenting Soil Properties in the Field and Laboratory
The consistent use of standard procedures to describe soils in the field, analyze soil samples in the laboratory, and classify soils in a way that effectively organizes knowledge of the nation’s soils is essential for carrying out an effective soil survey program.
3.1.1
Properties Used to Describe Soils in the Field
In the USA, hundreds of soil scientists working over a span of more than a century have collectively studied and recorded information from hundreds of thousands of soil profiles as part of the National Cooperative Soil Survey (NCSS). Such a large undertaking requires a standard approach so that soil descriptions can be compared, grouped, interpreted, and classified consistently. A soil profile is a 2-dimensional face observed in a pit, road cut, or other exposure large enough to reveal the boundaries of soil horizons and the largest structural units. The standards for describing soil profiles have been recorded in successive versions of the Soil Survey Manual (Soil Survey Division Staff 1993) and more recently, in the Field Book for Describing and Sampling Soils (Schoeneberger et al. 2012). The process of describing the soil generally begins by exposing a soil profile over a lateral distance of about 1 m and to a depth of 1.5–2 m (Fig. 3.1). From the exposure depicted in Fig. 3.1, a sequence of layers or horizons can be observed ranging from the darkened surface layer (“A” horizon), to a lighter colored subsurface layer (“E” horizon), through the subsoil (“B” horizon), and, to the underlying, little-altered parent material (“C” horizon). C.A. Ditzler (&) USDA-Natural Resources Conservation Service, Lincoln, NE, USA e-mail: [email protected] © Springer International Publishing AG 2017 L.T. West et al. (eds.), The Soils of the USA, World Soils Book Series, DOI 10.1007/978-3-319-41870-4_3
Soil scientists use a shorthand nomenclature to record the kind and thickness of horizons present in the soil profile. Master horizons are denoted with a capital letter (Table 3.1). Lower case letter suffixes can be used to differentiate within master horizons to describe some important aspects of the soil material or infer important soil-forming processes (Table 3.2). Each horizon identified in the profile is labeled with the appropriate nomenclature. Once the kind and thickness of soil horizons is recorded, additional properties are noted for each horizon. Properties commonly recorded for each horizon include those shown in Table 3.3. A typical example of a standard narrative soil horizon description is as follows: Bt - 20 to 35 cm; yellowish brown (10YR 5/4), silt loam; 5 % gravel fragments; moderate medium subangular blocky structure; friable; few fine distinct light gray (10YR 7/2) redox depletions; common fine black (10YR 2/1) iron-manganese concretions; many dark yellowish brown (10YR 5/4) clay films on ped faces and in pores; common fine and medium roots; common fine tubular pores; slig
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