Abstract In soil micromorphology most studies are done with light and electron microscopes on thin sections from selected samples. Information is obtained on nature, distribution, size, form, quantity, etc. of soil constituents and features. Significant data, not readily obtainable from thin sections, can be supplied by using sieve fractions. Amongst such data are specific soil structures (rounded macro-aggregates, micro-aggregates and coated plant fragments) which may, partly or wholly, have been made by soil biota. During the study of water repellency of agricultural and uncultivated sandy soils in the southwestern Netherlands, each sample was sieved, washed and treated with hydrogen peroxide. By measuring the water drop penetration time (WDPT) of a soil sample and of its sieve fractions, and by microscopic examination of soil components and features in each of these, one can indicate which soil constituents are important to the building up of water repellency. The appearance and degree of water repellency are closely related with organic matter (plant fragments, roots, etc.). This organic matter can form a part of soil structures (e.g. micro- and macro-aggregates) or be the principal component itself. Water repellency (WDPT > 5 s), caused by micro-aggregates, can already occur in wettable soils, in the finest ( 2000 μm) were wettable. With increasing water repellency, from slightly to extremely water-repellent soils, more sieve fractions are occupied by soil structures and components that contain water-repellent organic remains, e.g. macro-aggregates, plant fragments and coatings on sand grains. Most of these structures and micro-aggregates have presumably, partly or wholly, been made by soil biota. Conversely, the degree of water repellency of soils can be reduced by decomposition of organic matter and by coating of plant fragments with fine non-water-repellent soil materials; processes in which soil biota are also active.
[1]
Louis W. Dekker,et al.
Water repellency in the dunes with special reference to the Netherlands
,
1990
.
[2]
P. King.
Comparison of methods for measuring severity of water repellence of sandy soils and assessment of some factors that affect its measurement.
,
1981
.
[3]
Ag Waters,et al.
Aggregate hierarchy in soils
,
1991
.
[4]
L. Debano.
Water repellent soils: a state-of-the-art
,
1981
.
[5]
J. Tisdall,et al.
Stabilization of Soil Aggregates by the Root Systems of Ryegrass
,
1979
.
[6]
Leonard F. DeBano,et al.
Soil wettability: A neglected factor in watershed management
,
1965
.
[7]
R. Miller,et al.
Nature of the Organic Coating on Sand Grains of Nonwettable Golf Greens1
,
1977
.
[8]
J. Loch,et al.
Submicroscopy and chemistry of heavy-metalcontaminated precipitates from column experiments simulating conditions in a soil beneath a landfill
,
1983
.
[9]
J. Oades,et al.
The use of dispersible clays to reduce water repellency of sandy soils
,
1989
.
[10]
A. Rovira,et al.
Ultrastructure of the root-soil interface
,
1983
.
[11]
D. Mcghie,et al.
The Effect of Plant Top Material on the Water Repellence of Fired Sands and Water Repellent Soils
,
1981
.
[12]
B. Carbon,et al.
Water repellence in sandy soils of South-Western Australia. II. Some chemical characteristics of the hydrophobic skins
,
1972
.