Title:
|
Some studies on the effects of long-term stockpiling of soils
|
During many quarrying, civil engineering and landscaping
schemes topsoil is stripped from the site and stored in large heaps.
They remain in situ for many years before the soil is re-used and
it is generally believed that there is a great reduction in the
'quality' of the soil during that period.
A study of stockpiles of different sizes, age, soil type and
method of construction has revealed that biological, chemical and
physical changes do occur, mainly as a result of anaerobic conditions
within the stockpiles, but also as a result of mechanized handling
under unfavourable conditions. Visible changes occur within 0.3 ni of
the surface of the clayey textured stockpiles, but only below 2 m depth
for sandy textures. No visible changes were noticed within the sampling
depth of the heaps which were created by techniques other than the
earthscraper method whereby soil is not compacted by machinery. These
visible changes are accompanied by chemical changes, particularly in
the form of nitrogen, iron and manganese present, but also in the content
of available nutrients (P, K and Mg), pH and organic matter levels.
Biological changes include reductions in potential for
mycorrhizal infection, earthworm biomass and population and to a lesser
extent in soil microbial biomass.
Physical changes include reduction in aggregate stability
measured on 1-2 mm aggregates accompanied by considerable variation with
depth, increase in bulk density mainly on stockpiles constructed by
earthscrapers. Laboratory work has indicated that stockpiled soils
attained higher bulk densities at equivalent pressures and moisture
content than corresponding unworked soils. The breakdown of the
domain structure in stockpiles was sharply revealed by scanning electron
microscopy. The soil atmosphere in the stockpiles contains high levels
of carbon dioxide, methane, ethane and ethylene but these did not reach
critical limits.
Limited evidence suggests that many of the adverse effects
quickly disappear when the soil is respread.
|