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4.1Introduction
The following differentiae are used to distinguish families/series of mineral soils during the soil survey of Kuwait (KISR 1999a, b) using the guidelines of USDA-NRCS (Soil Survey Staff 1999), which is upgraded to the latest edition of Keys to Soil Taxonomy (Soil Survey Staff 2014). The class names of these differentiae are used to form the family name. The class names are listed and defined in the same sequence in which they appear in the family names. The names of the soil family are separated by comma (Typic Haplocalcids, sandy, mixed, hyperthermic). Exception is in the soil family with Typic Torripsamments subgroup, where particle size class is redundant, because Typic Torripsamments (by definition) are sandy. If more than one phase is needed to be expressed, they are separated by hyphen (Typic torripsamments, mixed, hyperthermic, shallow-lithic).
Particle-size classes and their substitutes
Mineralogy classes
Cation-exchange activity classes
Soil temperature classes
Soil depth classes
Phases of soil taxa
4.2Definition of Particle-Size Classes
The term particle-size class is used to characterize the grain-size composition of the whole soil, including both the fine earth and the rock and pararock fragments up to the size of a pedon, but it excludes organic matter and salts more soluble than gypsum. The particlesize “texture” classes in pedologic classifications have been based on percentages, by weight, in the fraction less than 2.0 mm in diameter. Fine earth refers to particles smaller than 2 mm in diameter.
4.2.1 Control Section for Particle-Size Classes
The particle-size and substitute class names listed below are applied to certain horizons, or to the soil materials within specific depth limits, that have been designated as the control section for particle-size classes and their substitutes. The
4.2 Definition of Particle-Size Classes |
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lower boundary of the control section may be at a specified depth (in centimeters) below the mineral soil surface or it may coincide with the upper boundary of a root-limiting layer (defined below).
4.2.1.1 Root-Limiting Layers
The concept of root-limiting layers as used in the Kuwait Soil Taxonomy defines the base of the soil horizons (a petrocalcic horizon, a petrogypsic horizon, a lithic contact) considered for most differentiae at the family level.
4.2.1.2Key to the Control Section for Particle-Size Classes and Their Substitutes
The following list of particle-size control sections for the soils of Kuwait is arranged as a key to allow the user of the Kuwait Soil Taxonomy to make the correct classification by going through the key systematically, starting at the beginning and eliminating one by one all classes that include criteria that do not fit the soil in question. The soil belongs to the first class for which it meets all of the criteria listed.
A.For mineral soils that have a root-limiting layer (listed above) within 36 cm of the mineral soil surface, from the mineral soil surface to the root-limiting layer; or
B.Between the lower boundary of an Ap horizon or a depth of 25 cm below the mineral soil surface, whichever is deeper, and the shallower of the following:
(a)a depth of 100 cm below the mineral soil surface or (b) a root-limiting layer.
4.2.1.3 Key to the Particle-Size and Substitute Classes
The key to the soils of Kuwait is arranged to allow the user of Kuwait soil taxonomy to make the correct particle-size distribution classification by going through the key systematically, starting at the beginning and eliminating one by one all classes that include criteria that do not fit the soil or layer in question. The class or substitute name of each layer within the control section must be determined from the key. If any two layers meet the criteria for strongly contrasting particle-size classes, the soil is named for that strongly contrasting class. If the soil has none of the strongly contrasting classes, the weighted average soil materials within the particle-size control section generally determine the class. Exceptions are soils that are not strongly contrasting and that have a substitute class name for one or more parts of the control section. In these soils the class or substitute name
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of the thickest (cumulative) part within the control section is used to determine the family name.
The sandy-skeletal, coarse-gypseous, sandy, loamy, coarse-loamy, fine-loamy particle-size and substitute classes have been identified in the soils of Kuwait. The gypseous-skeletal and fine-gypseous substitute classes are not recorded in the soil survey for the state of Kuwait, but are likely to be recorded in future soil survey work in Kuwait, therefore, these are also added in the following section.
Throughout the control section, meet one of the following particle-size class criteria.
1.The mineral; soils have, in the fraction less than 20 mm in diameter, 40 percent or more (by weight) gypsum and one of the following:
a.A total of 35 percent or more (by volume) rock fragments.
Gypseous-skeletal
or
b.Less than 35 percent (by volume) rock fragments and 50 percent or more (by weight) particles with diameter of 0.1 to 2.0 mm.
Coarse-gypseous
or
c. Less than 35 percent (by volume) rock fragments.
Fine-gypseous
2.The mineral soils that have a total content of rock fragments, plus any artifacts 2 mm or larger in diameter which are both cohesive and persistent, of 35 percent or more (by volume) and a texture class of coarse sand, sand, fine sand, loamy coarse sand, loamy sand, or loamy fine sand in the fine-earth fraction (Fig. 4.1).
Sandy-skeletal
3.Have a texture class of coarse sand, sand, fine sand, loamy coarse sand, loamy sand, or loamy fine sand in the fine-earth fraction (Fig. 4.2).
Sandy
.
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0 cm
Ak
20 cm
Bk
60 cm
Fig. 4.1 Sandy-skeletal soil particle-size class
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0 cm
Ak
20 cm
Ck
65 cm
Fig. 4.2 Sandy soil texture in a Typic torripsamments