Results from a
combination of abiotic and biological processes
acting on
sediment or rock.
Abiotic:
weathering, leaching, mechanical breakdown
Biotic:
accumulation of organic material, acid production
Soil Profile:
Horizons (Fig
4.1): 0, A, E, B, C, R
0 Horizon:
surface, Litter, Duff, no mineral component
greatest
change in temp, moisture
may
fluctuate seasonally
most
decompositon occurs here
A Horizon: first
mineral layer, contains organic matter,
mostly
DOM
Gradient
of POM to attenuated DOM
Leaching
of minerals, clays from water percolation
E Horizon: zone
of maximum leaching of minerals, little organic matter
B Horizon: Zone
of accumulation
Silicates,
clay, iron, aluminum
May
be above a solid clay layer; clay pan:
perched aquifers, wet prairie
C Horizon:
unaltered parent material: marine, alluvial sediment
R Horizon:
unaltered bedrock
Rock fragments:
larger than 2.0 mm
Sand: 0.05-2.0
mm
Silt: 0.002-0.05
mm
Clay: <0.002
mm
“well
sorted”
Texture
determines pore space or interstitial space, 50% pore space best
Clay important
to soil chemistry, processes
Clay mineral
structure: Layers of Aluminum or Silica Fig 4.5, 4.6
net
negative charges
Cation
Exchange (Fig. 4.7) in order of binding strength:
Al3+,
H+, Ca2+, Mg2+, K+, NH+,
Na+
Cation
Exchange Capacity: number of cation binding sites per unit soil
Percent
Base Saturation: % of binding sites
occupied by Ca2+, Mg2+,
K+, Na+
Soil
fertility dependent on CEC, %BS, Salinity, metals
Soil Water:
Field Capacity:
amount of water held 2-3 days post rain
Consists
of capillary and hygroscopic water
Available Water
Capacity: defined by vacuum extraction
(differs
by plant species) Wilting Point Figure 4.4
AWC, Drainage
dependent on soil texture:
Excessively
drained to poorly drained
Saturated soils:
anaerobic, accumulated organic matter, histosols