Agriculture Reference
In-Depth Information
Table 1.1
(continued)
Factors
Components
Characteristics and active agents
Features of soils formed
Organisms
Plants
Animals
Humans
Plant species differ in the chemical
properties of their leaf litter; roots
and earthworms form channels;
microorganisms decompose and
humans add, organic residues
Under conifers and heath, Fe and Al
organic complexes translocated to form
podzols and podzolic soils; humified
organic matter forms under deciduous
trees and grassland
Topography
Slope
Water and gravity move material down
steep slopes; solifluction occurs in
thawed-over-frozen soil
Slopes facing the equator are warmest
Soils at the top of slopes are shallow
with good drainage; depth increases
downslope but drainage usually is
poorer, so Fe colors change from
orange-red through yellow to blue-gray
Aspect
Time
Tens to hundreds of years (recent volcanic
eruptions, human activity) to tens of
thousands of years (glacial and interglacial
periods of the Pleistocene—box 1.2) to
more than 1,000,000 years (in stable
landscapes)
Modifies the action of the other factors
Soils range from shallow with little
profile development to deep with
well-developed profiles as time passes;
younger soils are generally more fertile
a
Chemical symbols for the elements are explained in chapter 3.
