Soil Degredation

John Wesley Powell

“The soil is the one indestructible, immutable asset that the nation possesses. It is the one resource that cannot be exhausted, that cannot be used up.” -

Lloyd Noble

“No civilization has outlived the usefulness of its soils. When the soil is destroyed, the nation is gone.” -

Franklin D. Roosevelt

“The nation that destroys its soil destroys itself.” -

natural processes affecting soil degredation

in both hatural and agricultural ecosystems

1. erosion

2. compaction

3. acidification

4. desertification

5. salinization

accelerate

human activity can __________ these natural processes

natural resources on which that existence depends

a sustainable system is one where current and developing practices can continue without exhausting the…

erosion

when soil particles are detached, transported, ad deposited

• bare soil aggregates are exposed to energy in water and wind

wind, water, tillage

erosion can be caused by

detachment, transportation, deposition

the three processes in erosion

what makes soil susceptible to erosion

• texture

  • amount of silt, sand, or clay

• aggregation

  • strength and size of aggregates, how attached to each other

• soil water conditions

• soil health and erosion

• erosion and soil fertility

in terms of erosion, there are links between…

water and wind

what are the two types of erosion

types of water erosion

1. splash erosion

2. flowing water erosion

splash erosion

erosion caused by the power and force of a raindrop

types of flowing water erosion

1. sheet

2. rill

3. ephemeral

4. gully

5. stream bank

sheet erosion

type of water erosion where topsoil is eroded in even layers

rill erosion

type of water erosion where water hits soil particles and carries them away creating random, spuratic grooves

ephemeral erosion

type of water erosion where water carrying away soil particles, following natural grooves in land

rill and erosion

types of flowing water erosion that can be fixed by tilling

gully erosion

erosion caused by the deep tracks made by water in soil

• can evolved from ephemeral

filling it in

gully erosion can be fixed by…

stream bank erosion

type of water erosion that is cuased by soil eroding on edges of bodies of flowing water

removing vegetation

stream bank erosion can be worsened by __________ along the banks

bodies of water

eroded topsoil is transported to __________

effects of increased sediment in water

1. degrades water quality; discolors water

   • less attractive for swimming, fishing, recreation

   • reduced clarity affects plant and algae growth

2. decreased depth of lakes, decresed storage volume

3. sediment fills up lake beds, affects fish egg laying habitat

4. creates shallow water, more susceptible to evaporation

5. clogs hydrroelectriv dam turbines

6. increases cost of drinking water purification

landslides and mudslides

examples of rapid and extreme erosion are…

increases, decreases

rapid and extreme erosion results when water __________ weight of soil and __________ cohesion of soil

saltation, suspension, creep

what are the three types of wind erosion

saltation erosion

wind erosion where soil particles jump from one area to another

suspension erosion

wind erosion where soil particels are picked up by wind and transported elsewhere

creep erosion

wind erosion where soil particles roll across the surface of the soil

particles don’t aggregate

wind erosion moves sand particels first because the __________

1. up and down

2. along the contour

3. soil thrown down slope

what are the three causes of erosion resulting from tilling soil on slopes

up and down the slope

tilling __________ causes more soil to move downslope than upslope

along the contour

tilling __________ also moves more soil downslope

moldboard throws soil downslope

more soil is moved if a __________, which is usually preferred because better inversion is obtained this way

soil loss tolerance (T value)

amount of annual soil loss that can be tolerated while still maintaining high soil productivity

surface and subsoil

what are the two types of soil compaction

tilth

soil compactions has an effect on __________

surface crusting

• raindrops disperse aggregates

• particles settle into thin, dense layer

• most common in arid, semiarid regions

• effects:

  • reduced water infiltration and threfore increased runoff, erosion

  • reduced germination success

plow layer compaction

• results from loss of aggregation

• loss due to:

  • erosion

  • reduced organic matter levels

  • weight of field equipment

subsoil compaction

• compaction below the plow layer

  • characteristics of subsoil make it easier to compact

  • also harder to loosen and add organic matter to

• can be caused through transfer of surface compaction force

• or directly by pressure from a disk or plow

smaller and easier to move through the soil

lower horizions tend to have more clay because clay particles are

easier

soil layers with more clay are ___________ to compact

the topsoil is not

subsoil can be compacted even if…

axle load

subsoil compaction is caused by __________ (expressed in tons)

higher, deeper

the __________ the axel load, the __________ the stress will be transmitted into the soil

reduction

__________ of axel load reduces subsoil compaction

more easily

wet soil tends to compact __________ than dry soil

sand, clay

how much __________ vs __________ determines the plastic limit of the soil

consequences of soil compaction

• lossof pore space

  • pores are smaller

  • becomes hard when dry

  • increased resistance to penetration

• hormonal response of plants

  • slows down respiration and growth

soil acidification

when precipitation exceeds soil water holding capacity and what plants can use, it leaches soluble cations out of topsoil

• cations are replaced by hydrogen ions

subhumid and humid

soil acidification is most common in __________ regions (tropics, arctic, some coastal)

liming the soil (adding Ca)

soil acidification is treated by…

fertilizers

soil acidification is a natural process but can be acceleration by some __________

salinization

occurs when

• water evaporares from soil leaving too much salt behind

• water runs off andleaves salts behind

water casues salt accumulation in soil, water leaves for any reason, and leaves salt accumulation behind on soil surface

• deals with capliary action and capillary rise

arid and semi-ari

salinization is a challenge in __________ regions (SW USA, Middle East, AUstralia, China, parts of India)

excessive irrigation and rising groundwater table of water

salinization also occurs with…

tilling soil and mixing salt back into soil

salinization can be managed/solved by

wash it out of the soil

if salinization is too great, instead of tilling you must

competes with plants for water

salt raises osmotic potential of soil water and thus the soil…

sodification

• buildup of excess sodium (Na⁺) in soil

• less of a plant problem more of a soil problem

• a specific type of salinization

• breaks up aggregates

• pushes soil particles apart (lose structure) and crust forms

sodium acts as a dispersant, meaning it…

results of sodification

• loss of soil structure

• increased compaction

treatment of sodification

add gypsum to the soil and the flush with adequate amount of water to displace the negative mineral