HPU NCS2200 Soil formation
Transcript of HPU NCS2200 Soil formation
10.4 Soil Components
• Components of soil – mineral grains (clay, silt, sand, rock fragments), organic matter, water, gas.
air
25%
water
25%
mineral matter
45%
organic matter
5%
Soil Profile• Horizons – soils develop a layered structure, the layers are
called horizons; (from top)o O horizon – mostly litter and humus
• Litter – organic debris on the ground’s surface
• Humus – decomposed litter, increases water-holding capacity
o A horizon – mixture of humus, sand, silt, clay
• O + A = topsoil
o B horizon – subsoil, low organics
o C horizon – partially weathered rock
o Water moves through soil and leaches ions
• Water, ions, clay from “A” end up in “B”
10.4 Factors affecting soil
development• Rates of plant growth & decay – affects humus and
chemistry
• Slope aspect & steepnesso Aspect – the direction a slope faces
• Time – chemical weathering is usually slow
• Soil transport – streams and winds move sediments
Soil Texture• Determined by soil particles
o Sand – largest
o Silt – middle
o Clay – smallest
• Percentage of each particle within the volume give the soil type
• Use the soil triangle to determine soil type
1) Find PercentageOf each particleType
2)Follow the lines for each percentageUntil they intersectAt a point.This give the soilType.
1) Find PercentageOf each particleType
2)Follow the lines for each percentageUntil they intersectAt a point.This give the soilType.
Permeability and Porosity• Permeability
o The ability to transmit (or release) fluids (water)
• Porosityo The volume of spaces between the soil particles
Water Water
High permeability Low permeability
Fig. 10.17, p. 224
Porosity vs Permeability• The larger the particle size the larger the spaces between
particles BUT there are fewer spaceso Sand has a high permeability because of large pore SIZE
• Gives sand the ability to DRAIN a lot of water
o Clay has a high porosity because of the NUMBER of pores
• Gives clay the ability to HOLD onto a lot of water
https://www.youtube.com/watch?v=39FfOa1gTX4&list=PLXKxye83Oxiy0qHna6eBa6HMIcQZuJjph&index=6
SOIL EROSION AND
DEGRADATION• Soil erosion is the
movement of soil components, especially surface litter and topsoil, by wind or water.
►Soil erosion increases through activities such as farming, logging, construction, overgrazing, and off-road vehicles.
Figure 13-9
Soil Degradation• Degradation – to degrade or lower
the ability of the soiloMechanisms of Degradation
• Erosion
• Desertification
• Salinization
• Waterlogging
SOIL EROSION AND
DEGRADATION• Soil erosion lowers soil fertility and can overload nearby
bodies of water with eroded sediment.o Sheet erosion: surface water or wind peel off thin layers of soil.
o Rill erosion: fast-flowing little rivulets of surface water make small channels.
o Gully erosion: fast-flowing water join together to cut wider and deeper ditches or gullies.
Global Outlook: Soil Erosion
• Soil is eroding faster than it is forming on more than one-third of the world’s cropland.
Figure 13-10
Desertification: Degrading Drylands
• About one-third of the world’s land has lost some of its
productivity because of drought and human activities that reduce or degrade topsoil.
Figure 13-12
Soil Degradation
• Causes of
Desertification
Overgrazing
Agricultural
overuse
Deforestation
Urban
development
Desertification – the complete loss of topsoilPreventing the remaining soil from retaining water and nutrients creating infertile substance
Moderate Severe Very severe
Soil Degradation
• Salinization
o Increase in the salt content of the soil due to irrigation
• Waterlogging
o Impermeable clay layer below soil traps water innundating root systems
Salinization and Waterlogging of Soils: A Downside of Irrigation
• Example of high evaporation, poor drainage, and severe salinization.
• White alkaline salts have displaced cops.
Figure 13-14
Fig. 13-15, p. 281
CleanupPrevention
Soil Salinization
Solutions
Reduce irrigation
Switch to salt-
tolerant crops
(such as barley,
cotton,
sugarbeet)
Flush soil
(expensive and
wastes water)
Stop growing crops
for 2–5 years
Install underground
drainage systems
(expensive)
Case Study: Soil Erosion in the U.S. – Some Hopeful
Signs
• Soil erodes faster than it forms on most U.S. cropland, but since 1985, has been cut by about 40%.o 1985 Food Security Act (Farm Act): farmers receive a subsidy for taking highly
erodible land out of production and replanting it with soil saving plants for 10-15 years.