Agriculture Reference
In-Depth Information
A. Particulate Structure
The soil is loose with no interlinking between particles‚ e.g.‚ unconsolidated sands.
B. Massive Structure
1. Sintered Structure
The soil is moderately cemented‚ it may be slightly porous or penetrated by plant roots or faunal channels‚ e.g.‚
earthworm burrows. May be divided artificially into coherent clods.
2. Cemented Structure
The soil is bound by hard precipitated cements (oxides‚ organic matter‚ carbonates‚ silica) which fix the
primary units into a hard resistant mass. This mass may range from discontinuous ( e.g. concretions) to
continuous structures such as iron pans‚ calcareous hard pans‚ etc.
C. Fragmentary Structure
1. Fine aggregate structures
i . These include aggregates up to approximately 1 mm equivalent cylindrical diameter (ECD); they result from
chemical linkages involving interactions between organic matter and clays‚ metal hydroxides and precipitated
humic substances. They may include the excrements of small animals.
ii. Built-up (agglomerative) structures. These aggregates are formed through soil working‚ either through the
agencies of soil animals or man:
a. Granular structures include subspherical aggregates ranging from I mm to 1 cm ECD and are often found
in the surface layers of tilled soils:
b. crumb structures are irregularly-rounded aggregates ranging from 1 mm to 1 cm ECD;
c. nutty structures are irregularly-rounded aggregates greater than 1 cm ECD.
2. Fissure structures
i. Blocky
structures are coherent‚ isodimensional aggregates with sharp edges;
they range
from a
few
millimetres to several centimetres in size.
ii. Prismatic structures are prism-shaped aggregates in which the vertical dimension is the greatest (to >20 cm).
Columnar structures are prisms with rounded tops.
iii. Lamellate or platy structures have their greatest dimension in the horizontal plane‚ e.g.‚ fragipans.
Search WWH ::




Custom Search