soil resources

pedosphere

pedon + sfaira
- foundation of terrestrial life
- skin of the earth
- supports life on earth

makeup of the pedosphere

25% air, 25% water, 45% minerals, 5% organic matter

how do soil form?

weathering of rocks

how does the parent material affect soil formation?

where the soil came from

residual soil (parent material)

soil formed on-site
- weathering of underlying rocks

transported soils (parent material)

parent material was carried from elsewhere, and then deposited

how does climate affect soil formation?

temperature, rainfall, and moisture affect the pattern and intensity of the process

what happens in dry and cold climates? (soil formation)

slower process

what happens in moist and warm climates? (soil formation)

faster process

topography

physical, natural features of the land

how does the gradient of the slope affect soil?

the gradient of a slope affects the water flow and erosion of the soil

soils that form in steep slopes are ___________?

thinner due to higher rate of erosion

how do biological factors affect soil formation?

animals & microorganisms - burrow
plants - root wedging
microorganisms - affect nutrient and chemical exchange between roots and soil
humans - agriculture & urbanization

how does time affect soil formation?

1cm of soil - 200-400 years
- the longer, the thicker & more layers the soil has

step by step of soil formation

1. bedrock disintegrates
2. organic materials facilitate disintegration
3. horizons form
4. developed soil can support thick vegetation

soil profile

arrangement of soil horizons

soil horizon

layers of soil parallel to the surface

o horizon

loose and partly decayed matter
- soil, regolith

a horizon

mineral matter mixed with some humus
- soil, regolith

e horizon

light colored mineral particles, zone of eluviation and leaching
- soil, regolith

b horizon

accumulation of clay, iron, and aluminum from above, zone of illuviation
- soil, regolith

c horizon

partially altered parent material
- regolith

r horizon

unweathered parent material
- bedrock

gelisols

frozen soil
- coldest regions

histosols

highly organic soil
- wet & dark

how do soils get their dark color?

organic matter content

spodosols (wood ash)

sandy & acidic soil
- moist climate
- supports dense forests

andisols (dark soil)

volcanic ash

oxisols

very weathered soil
- tropical climate

vertisols

clay-like and swells/shrinks depending on water content

aridisols

dry soil
- arid regions

ultisols

strongly leached and weathered soil
- red clay

mollisols

soft, deep, fertile
- in grassland ecosystems

alfisols

moderately weathered and productive soil

inceptisols

slightly developed, young soil
- in steep slopes & mountain ranges

entisols

newly formed soil
- in steep rocky land

soil texture

proportions of particle sizes
- sand, clay, silt
- loam (mix of all three)

soil structure

arrangement of particles in soil that affect its porosity

granular structure

rounded, breadcrumb-like

crumb structure

- rounded, breadcrumb-like
- bigger than granular

prismatic structure

long, vertical, rectangular dimensions

columnar structure

- long, vertical, rectangular dimensions with rounded tops
- salt caps

platy structure

flat layers stacked on top of each other

single-grained structure

no aggregation and separated from each other
- sand-like

blocky structure

flattened, cube-like, with sharp edges

subangular blocky structure

flattened, cube-like, with rounded edges

soil color

indicates presence of organic matter, parent material, weathering, and permeability

soil color is influenced by

- parent material
- organic matter
- iron content
- moisture

dark-brown soil color

moderate organic matter & iron oxide

black soil color

high levels of organic matter

red soil color

- good drainage
- iron is oxidized more readily, thus the rusty color

yellow to yellow-brown soil color

- poorer drainage than red soil
- iron are hydrated (no rusty color)

gray, blue, green soil color

- very poor drainage & waterlogging
- iron and manganese form compounds that cause these colors due to the lack of air

white, pale, bleached soil color

- bleached or washed out
- heavy rainfall or drainage causes iron & manganese to be leached out