Agriculture Reference
In-Depth Information
Triangular diagrams (Figure I.4) permit allocation of soils to broadly-defined textural
classes and this can be of considerable value in predicting their handling and tillage
properties. This may also be of use in biological characterisation since, as discussed
below, moisture and organic matter relationships depend to a substantial degree on texture.
Figure I.4 presents the uppermost mineral horizons of a subset of soils from Table I.4,
classified according to International standards (McDonald
et al
., 1990). It should be noted
that because of the differing definition of silt in the British Standard System, the posi-
tions of the soils described in Avery (1990) are only approximate. Further, soil texture
normally alters with depth in the profile and the alfisol described by Murtha (1982)
(Table I.4, Figure I.3b) changes abruptly from a sandy loam to a sandy clay at
the transition between the E and B horizons (
i.e
., at 22 cm).
Textural differences between selected major soil groupings
The proportions of the primary size fractions of the fine earth (the particle-size distribution)
often differ markedly between soils and horizons. Texture variation down the profile is
a characteristic of certain orders in the American system of classification, Soil Taxonomy
