Geoscience Reference
In-Depth Information
Fig. 18.6 Time change in
pH (open circle) and
exchangeable Al 3+ (filled
circle) in the 15-20 cm layer
of an acidic Kurosol initially
limed to a pH of 5.5
(0-10 cm) in 1992 (White
et al. 2000 ) Reprinted with
permission, CSIRO
Publishing, http://www.
publish.csiro.au/nid/72/paper/
EA98013.htm
(Greenland et al. 1997 ), without considering forest or urban surfaces. In agricul-
tural lands, the process of soil acidification is accelerated by the large amount of N
cycling through the system, when substantial amounts of organic products and
residues are removed. Permanent acidity may occur when H + and OH - generation
during mineral N uptake and transformation is decoupled, enriching the soil with
an excess of H + (White 2008 ). Urban and industrial inputs to the soil acidification
process are due generally to the release of forms of mineral sulfur and nitrogen,
which are converted to sulfuric or nitric acids, leading to acid rain and/or atmo-
spheric dry acid deposition.
Raising the pH of acidic soils through addition of lime materials is a very old
procedure. In 1882, Ruffen achieved this goal by adding oyster shells to acidic soil
in the coastal plain of Virginia, USA. With time, liming became a routine pro-
cedure for altering natural or anthropogenically induced soil acidity. Examples of
liming materials used in Australia and New Zealand are reviewed by White et al.
( 2000 ). Under field conditions, the positive effect of lime addition consists of a
combination of cementing and flocculation actions. Hoyt ( 1981 ) found that
application of lime to two Canadian soils increased soil pH (water) to the range of
5.5-6.5 causing a significant change in distribution of dry aggregates toward
coarser fractions, and increasing resistance of soil to compression. Liming is a
slow release process; the time required to change the pH of an acidic soil (Kurosol)
by surface application of lime materials is shown in Fig. 18.6 , where the change of
pH Ca from 4.1 to 5.5 occurred only 5 years after application.
The downward movement of liming products such as OH - and HCO 3 released
from CaCO 3 , through their diffusion or leaching, is overwhelmed by the buffering
capacity of soils. As a consequence, changing soil pH by liming into the subsur-
face regime can be achieved only by direct subsoil application of liming materials.
The slow release properties of the liming material, associated with continuous land
application of lime within sustainable agriculture management, can cause irre-
versible changes to soil acidity.
Increases in pH as a result of liming may cause a dispersion/flocculation pro-
cess that leads to irreversible changes in soil physical properties. At low pH, acidic
soils are normally flocculated because Al 3+ and H + activity in soil solution causes
Search WWH ::




Custom Search