|
|
| |
|
|
|
|
| |
Soil
Conservation : |
|
 |
| |
|
|
| |
Soil Conservation
- The Dust Bowl – a lesson in the importance of top soil
- Soil formation: Weathering
- Soil profiles and properties
- Erosion
- Conservation
- The Dust Bowl.
I. The Dust Bowl.
Soil is the weathered products of rocks and minerals that are capable of supporting plant life.
Discussed the Dust Bowl in the 1930s.
II. Weathering and soil formation
Weathering – a set of processes by which rocks and minerals are broken into smaller fragments
Three classes of weathering processes:
Mechanical – physical breakup of rocks and minerals without a change in their composition.
Includes processes such as frost wedging, abrasion during glacial or stream flow, mass wasting (gravity driven processes), heating and cooling, and actions of plants and animals.
Importance – mechanical breakup of a rock increases the surface area of the rock or mineral that is exposed to chemical reactions that can further break down the fragments.
Chemical – breakdown of minerals by chemical reactions with air, water, and other chemicals.
1) Solution – the dissolving of minerals, typically through reactions with weakly acidified water
2) Oxidation – “rusting” of iron-bearing minerals.
3) Hydration – incorporation of water into mineral structures
4) Hydrolysis – complex reaction that results in formation of clays
Biological – an increasing amount of research demonstrates that bacteria play direct roles in breaking down minerals.
Rate of weathering
Controlled by
(1) grain size,
(2) amount of precipitation,
(3) temperature,
(4) organic component,
(5) air and water pollution
III. Soil profiles and properties
Soil is typically layered into a series of vertical zones, as shown in the graphic.
Horizons O and A – the uppermost layers, which tend to be rich in organic material (remains of dead organisms)
A horizon is the zone of leaching.
Horizon B - referred to as the zone of accumulation. Less exposed to weathering and much less organic material than upper horizons.
Horizon C – coarsely fragmented bedrock.
Horizon R – the regolith or bed-rock.
Discussed laterite, caliche, and loess
Wind-blown silt deposits are known as loess. Loess deposits reach depths of several hundred meters in some areas and cover roughly 10% of the earth’s land area.
IV.oil Erosion
Rates of soil erosion vary dramatically from one region to the next depending on soil conservation practices and the peculiarities of topography and vegetative cover.
Key facts about top soil:
- Richest in organic matter and hence most fertile for crop production
- Lost first when erosion occurs.
- Crop production declines significant upon loss of top soil
- Soil eroding from fields is deposited in lakes and streams and damages their ecosystems.
- Rate of natural soil production is roughly 2-10 times slower than rate of soil loss in the United States. Centuries to thousands of years are required to replace the A horizon.
- Problems are significantly worse in 3rd World countries than in the United States. Globally, amount of farmland that is so degraded that it can no longer be used to produce crops is approximately equal to combined size of India and China.
- Most damaging practices are overgrazing, deforestation, poor agricultural practices, construction, and use of off-road vehicles.
- Federal government funds Soil Conservation Service, who advises farmers about techniques for soil conservation. Much progress has been made, but despite all of the money spent and research invested, soil erosion remains a significant problem in this country 60 years after preventive measures were implemented
V.Conservation
Techniques for slowing or stopping erosion rely on slowing motion of water or wind that can transport sediment. Ability of water or wind to transport sediment increases as the SQUARE of its velocity, so it is critical to slow them down.
- Wind breaks such as tree lines and strip-cropping.
- Contour plowing
- Terracing
- Planting cover crops to hold soil
- Removing marginal land from agricultural production
- Conservation tillage (land is not plowed)
- Sediment traps (positioned in gullies and drainage ways to capture sediment)
|
|
| |
|
|
|
|
 |
Adds |
|
