soil erosion

plsc204 final exam

about ___ of degraded land has suffered vegetative, but not soil degradation

60%

most land with degraded soils could be ___

easily restored or with considerable financial and technical investments

severely degraded soils are currently ___

useless for agriculture and would require major international assistance for restoration

about ___ of the soil degradation is caused by erosion by wind and water

85%

about ___ of all degraded soils are extremely degraded and incapable of restoration

.5%

___s move more soil material than all natural processes combined

humans

unintentional soil movement refers to ____

soil loss due to agricultural activities such as land clearing, tillage, overgrazing, and long periods without vegetative cover

As the natural vegetation is disturbed soil becomes ____

exposed to raindrops and wind leading to erosion and loss of soil, organic matter, and nutrients

impoverished soil can support only stunted vegetation, leaving ____

even less protective cover and not mass than before

_____ is a major cause of erosion

agriculture

3 basic steps of soil water erosion

1. detachement

2. transport

3. deposition

what is the first step of soil water erosion

 A raindrop speeding toward the ground.

what is the second step of soil water erosion

The splash that results when the drop strikes a wet, bare soil. Such raindrop impact destroys soil aggregates, encouraging sheet and interill erosion. Also, considerable soil may be moved by the splashing process itself.

what is the thrid step of soil water erosion

The raindrop affects the detachment of soil particles, which are then transported and eventually deposited in locations downhill

3 major types of soil water erosion

1. sheet erosion

2. rill erosion

3. gully erosion

what is sheet erosion

• Relatively uniform erosion from the entire soil surface

• Note that the perched stones and pebbles have protected the soil underneath from sheet erosion

what is rill erosion

• Initiated when the water concentrates in small channels (tills) as it runs off the soil

• Subsequent cultivation may erase rills, but it does not replace the lost soil

what is gully erosion

• Creates deep channels that cannot be erased by cultivation

• Although gully erosion looks the most catastrophic of the 3, far more total soil is lost by the less obvious sheet and rill erosion

agriculture increases erosion compared to ____

forested land

a ____ allows vegetative cover to be efficiently established on difficult to reach areas

hydroseeder

_____ are laid down over newly seeded grass to hold the seed and soil in place until the vegetative cover is established

erosion control mats or blankets made of plastic netting or natural materials

____ control the flow of water off cropland and prevent gully erosion

contour tillage and grassed waterways

_____ can be effective tools to reduce losses of runoff water and soil

narrow grass hedges

erosion control methods

• sod and rip-rap

• barriers

• water bar

rip-rap prevents ___

gully erosion, reduces soil loss, and guides runoff around the perimeter of a construction site

universal soil loss factors

• rainfall erosivity

• soil erodibility

• topography

• cover management

• support practices

main 3 processes of wind erosion

1. soil creep

2. saltation

3. suspension

soil creep involves

sliding and rolling

saltation involves

bouncing

suspension involves

longer-term dispersal by wind

factors affecting wind erosion

• wind velocity

• surface roughness (tillage effects, residues)

• soil properties (mechanical stability, BD, moisture, texture)

• vegetation (slows wind, roots hold soil in place)

_____ is the primary mode of wind erosion

saltation

control of wind erosion

• soil moisture

• wind breaks

• soil cover (tillage)

the effect of windbreaks extends ___ times the height of trees

10-20