Intro Soil Geo Ch. 3 Flashcards
Where can the biggest changes in soil properties be seen?
top 30 to 1000cm
more than 75% of roots are located here.
how does soil differ from its parent material?
phase distribution, texture, colour, strucutre, mineralogical composition and presence of organic matter.
three soilphases
solid liquid, gas
mineral soil
less than 15-20% organic matter
organic soils
more than 15-20% organic matter.
examples of soil life
bacteria, fungi, protozoa, arthopods, earthworms.
calculation to find pore space.
100% - volume of solid%poros
why is porosity usually 50% instead of 25%?
aggregates - naturally occurring clusters of soil particles wiht relatively much space between them.
voids and channels created by roots and animals.
soilstruture
arrangement of soil particles.
primary minerals
quartz and silicates. usually present as sand and gravel.
secondary minerals
formed from primary minerals, those in sedimentary soils have arried in material eroded from upstream residual soils
residual soils
originate locally from in situ weathering of rock.
soil morphology
the soil’s visible and tactile properties including its architecture. It is determined by CLORPT.
soil horizon
layers parallel to the soil surfacethat have morphological, chemical, and usually physical and biological characteristics that differ from over and underlying layers. The vertical succession of soil horizons makes up a soil profile.
pedogenesis
soil formation
include in a soil profile
date, location, altitude, position in horizonization
include in each horizon description
depth of top and bottom ofhorizon, colou, texture,organic matter content, presence of calcium, mottles, presence of water table or other notable features.
soil texture
the relative proportions of differently sized particles in the soil. We divide into a fine and coarse earth fraction.
USDA
United States Department of Agriculture
What are the 4 soil textures?
gravel (everything over 2mm)
sand (0.05 to 2 mm)
silt( 2 to 50 micrometres)
clay (less than 2 micrometres)
textural class
dependent on the mass ratio between sand, silt and clay, shown on a triangle graph
particle size frequency curve
a graph with a logarithmic x axis depicting particle size against percentage of particles.
which 3 main factors influence soil colour
organic matter content
water content
presence of iron and manganese.
when do you get darker soils?
organic matter coatings, wet soil by both moisture and oxidation.
pigments occur where?
coatings on larger grains and as small independent particles between larger grains.
mottles
spots of colour in a matrix of another colour. Used to interpret natural drainagecondition of the soils. Found at the depth at which excess water accumulates as it cannot drain any deeper.
munsell colour charts
used to determine the colour of the soil. This is standardised.
