Agriculture Reference
In-Depth Information
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
Kinetic limited
0.00
0.00
0.05
0.10
0.15
0.20
D Na-total (mol Na m - 2 year -1 )
Fig. 6.4. Chemical weathering rate represented by the removal of Na from the regolith, plotted against
the total Na denudation rate (from Rasmussen et al ., 2011). Filled squares represent sites with HI > 1,
while open triangles are sites with HI < 1. Sites plotting close to the 1:1 line corresponding to erosion-
limited conditions for soil formation coincide with virtually complete depletion of Na from the regolith.
Dryer sites (HI < 1) plot more closely to the line of kinetic-limited weathering, where erosion is minimal
and the rate of soil formation is controlled by the rate of chemical alteration of the regolith.
of water availability and temperature on
weathering as a fundamental set of soil-
forming processes.
and maintaining the gene pool of the terres-
trial environment ( Fig. 6.2) .
Central to these functions is the devel-
opment of soil structure, the building of soil
aggregates. Soil carbon is a major factor in
this process. As lichens and plants colonize
the surface of parent material, the photosyn-
thate organic carbon provides an energy
and carbon source to support heterotrophic
microorganisms with a vital role as decom-
posers. Living organisms and extracellular
products of decomposition such as polysac-
charide adhere to larger fragments of de-
composing biomass, and also bind rock and
mineral fragments. These accretions form
the larger aggregates in the size fraction of
0.25-1 mm. These are associated with rapid
turnover of carbon and associated nutrient
elements from the decomposing organic
material, thus rendering nutrients bioavail-
able for new plant productivity. The abun-
dance of decomposers also supports grazing
populations, presumably protozoa, but also
soil fauna that further transform ingested
biomass, produce faecal material and also
The Development of Soil Function
The operation of Earth's weathering engine
(Fig. 6.1 ) as influenced by the interrelated
factors of soil formation (Jenny, 1941) does
not reveal fully the true nature of soil. As
soil forms, the range of chemical, biological
and physical processes that occur gives rise
to important soil functions that support eco-
system services, with impacts far beyond
creating soil as a geological material that ac-
cumulates at Earth's surface. These func-
tions include the storage and transmission
of water, filtration and transformation of
pollutants to reduce contamination in infil-
trating water, transformation and recycling
of nutrients to enhance their bioavailability,
storage of carbon and nitrogen and reduc-
tion of greenhouse gases, sustaining habitat
 
 
 
Search WWH ::




Custom Search