Land evaluation and related glossaryCompiled, and with editorial comments, by D G Rossiter |
A LQ can often not be measured or estimated directly, instead it must be inferred from a set of diagnostic LCs.
In the context of irrigated agriculture, a land utilization type refers to a crop, crop combination or cropping system with specified irrigation and management methods in a defined technical and socio-economic setting.
In the context of rainfed agriculture, a land utilization type refers to a crop, crop combination or cropping system with a specified technical and socio-economic setting.
A land utilization type in forestry consists of a technical specifications in a given physical, economic and social setting
Its horizontal boundaries are where it grades to deep water or to barren areas of rock or ice.
The lower boundary that separates soil from the not-soil underneath is most difficult to define. Soil consists of the horizons near the earth's surface which, in contrast to the underlying rock material, have been altered by the interactions, over time, between climate, relief, parent materials, and living organisms.
However, soil ... does not need to have discernible horizons, although the presence or absence of horizons and their nature is of extreme importance to its classification. In the few places where the soil contains thin cemented horizons that are impermeable to roots, it is considered to be as deep as the deepest cemented horizon. More commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biologic activity. Thus the lower limit of soil is normally the lower limit of biologic activity, which generally coincides with the common rooting depth of native perennial plants.
If, however, either biological activity or current pedogenic processes extend to depths greater than 200 cm, the lower limit of the soil that we classify is arbitrarily set at 200 cm. For certain soil management purposes, layers deeper than the lower boundary of the soil that we classify must also be described if they affect the content and movement of water and air in the soil of the root zone."
(From Keys to Soil Taxonomy, 7th edition.; emphasis & punctuation added)
[The soil series] is conceived as a grouping of soils which are alike in their characteristics and behaviour in the landscape. Soils within a series are developed on the same parent material in the same environment and have profiles that are almost alike, with horizons that are similar in their vertical sequence, thickness and morphological properties.Note that the emphasis is on a recognizable field unit that can serve as an information carrier for interpretations.
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Each series is intended to have a unique combination of site features and morphological characteristics which can be assessed, for the most part, in the field.
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Once a series has been defined and mapped according to its differentiating characteristics, many accessory properties of practical importance can be predicted.
According to the SSSA glossary: :
"The lowest category of U.S. system of soil taxonomy; a conceptualized class of soil bodies (polypedons) that have limits and ranges more restrictive than all higher taxa. Soil series are commonly used to name dominant or codominant polypedons represented on detailed soil maps. The soil series serve as a major vehicle to transfer soil information and research knowledge from one soil area to another."
According to the USDA Soil Survey Manual:
"The soil series category is the most homogeneous category in the taxonomy used in the United States. As a class, a series is a group of soils or polypedons that have horizons similar in arrangement and in differentiating characteristics. The soils of a series have a relatively narrow range in sets of properties. The surface layer and such features as slope, stoniness, degree of erosion, and topographic position may vary unless these factors are associated with significant differences in the arrangement of horizons.Note the insistence that the Series be the lowest categorical level of Soil Taxonomy. Many authors and especially mappers have criticized this as being unrealistic. See "taxadjunct".Soil series are differentiated on all the differentia of the higher categories plus those additional and significant characteristics in the series control section. Some of the characteristics commonly used to differentiate series are the kind, thickness, and arrangement of horizons and their structure, color, texture, reaction, consistence, content of carbonates and other salts, content of humus, content of rock fragments, and mineralogical composition. A significant difference in any one of these can be the basis for recognizing a different series. Very rarely, however, do two soil series differ in just one of these characteristics. Most characteristics are related, and generally several change together. "
It is a branch of applied physical geography, and draws heavily from geomorphology and theories of pedogenesis to produce accurate maps.
"Taxadjuncts are polypedons that have properties outside the range of any recognized series and are outside higher category class limits by one or more differentiating characteristics of the series. The differences in properties are small so that major interpretations are not affected. A taxadjunct is given the name of an established series that is most similar in characteristics. It is an adjunct to, but not part of, the named series. It is treated as if it were a member of the named series, and its interpretations are similar to those for comparable phases of the series for which it is named. The difference from the established series is described.In short, the taxadjunt only arises because the insistence of Soil Taxonomy that the series must be the lowest category in Taxonomy. The taxadjunt is in fact in nature part of a recognizable and mappable series, which happens not to obey the limits set down in Soil Taxonomy at a higher categorical level.Example: A potential series is in a fine-silty family particle size class, marginal to fine-loamy; however, it differs from an established fine-loamy series in only particle size and no appropriate fine-silty series has been identified. The potential series is given the name of the established series, and a new series is not proposed."