Educators PPT file chapter 6

Chapter 6
Environmental Science, Soil Conservation, and Land Use Management

Sustainability is
existence maintained
over time. A sustainable
system is one where
current and developing
practices can continue
without exhausting the
natural resource on
which that existence
depends. Resources are
renewed or replenished
rather than depleted.
Sustainability
Image Credit: USDA
soils4teachers.org/KSKL

Best management practices are
activities that landowners and
managers can use to help
conserve soil and water
resources. BMPs are proven to
reduce soil erosion and pollution
and improve water and
environmental quality.
Management practices can
address the source of the
problem, the outcome, or both.
Best Management Practices
Image Credit: USDA-NRCS
Fig. 6-18. Contour strip cropping.

NATURAL PROCESSES
AFFECTING SOIL DEGRADATION
Natural processes that affect soil in both natural and
agricultural ecosystems include erosion, acidification,
desertification, and salinization.

Erosion occurs when
soil particles are
detached, transported,
and deposited.
Erosion
Image Credit: Know Soil Know Life, D. Lindbo, D. Kozlowski, and C. Robinson - Editors, © 2012
Fig. 6-1.

Because of the way they are
managed, agricultural
ecosystems may experience
accelerated wind and water
erosion, so soil erodes faster
than it forms. If more soil
erodes than forms, the amount
of available soil decreases over
time, threatening long-term
sustainability.
Erosion
Image Credit: USDA

Water erosion is caused by two detaching forces: raindrop impact and flowing
water. Three types of water erosion can occur: sheet, rill, and gully.
Erosion by Water
Fig. 6-9. Rill erosion Fig. 6-10. Gully erosion

Water control methods
attempt to decrease the
kinetic energy of the water by
limiting soil detachment,
decreasing transportation, and
encouraging deposition. The
most effective way to control
erosion is to keep the soil
surface covered, either with
growing plants or residues
from past crops.
Water Erosion Control Methods
Fig. 6-11. Irrigated cotton planted
after wheat.

Wind erosion damages millions
of hectares of land in the United
States annually, especially in the
Great Plains. Less precipitation
in the West means there is less
vegetation. The landscapes are
generally flatter, with few hills
and trees to slow the wind at the
soil surface. The soils also tend
to have less organic matter to
hold aggregates together, making
the soils more susceptible to
wind erosion.
Erosion by Wind
Fig. 6-17(b). Conventional plowing.

Sand particles are
heavier and are moved a
few centimeters to a few
kilometers, but silt
particles can be carried
for a few hundred
kilometers and clays for
thousands.
Erosion by Wind
Image Credit: USDA

The main principles for
controlling wind erosion are
similar to those for controlling
water erosion: protect the
surface and reduce energy.
soils4teachers.org/KSKL Image Credit: Know Soil Know Life, D. Lindbo, D. Kozlowski, and C. Robinson - Editors, © 2012
Fig. 6-20. Conventional tillage left no
residues on the soil surface to protect it
from wind erosion.
Wind Erosion Control Methods

Fig. 6-24. Areas of the world most vulnerable to
human-induced desertification.
Desertification
Desertification is the extreme degradation of productive land in
arid and semiarid regions. It is a natural process associated with
global climate changes. Desertification can also be brought on
by improper management practices.

Grasslands adjacent to deserts
can have low precipitation
amounts, and such grasslands are
often used as rangeland for
grazing livestock. This can lead
to overgrazing, resulting in the
death of the perennial grasses.
The lack of soil cover increases
erosion of soil. Without
sufficient precipitation, the
perennial grasses do not recover,
and characteristic desert
vegetation encroaches.
Desertification
Fig. 6-25. Degraded rangeland with crusted soils and sparse annual
vegetation.

Adequate vegetative cover
should be maintained to
prevent accelerated erosion.
Range management BMPs
include controlling the
livestock stocking rate and
grazing intensity, keeping
livestock out of sensitive
areas, and providing
livestock with alternative
locations for water and
shade.
Fig. 6-26. Degraded rangeland improvement project.
Desertification Control Methods

Acidification occurs when base cations leach from the soil during times of
excess precipitation, leaving acidic cations behind. The pH decreases as the
soil becomes more acid. Producers managing acid farmlands regularly apply
lime (calcium carbonate or similar minerals) to mitigate the acid in the soil.
Acidification
Image Credit: USDA

Salinization, or the buildup of
salts, occurs when water
evaporates from soil and
leaves behind previously
dissolved salts. These salts
begin to accumulate in the
soil because there is little
rainfall to wash out, or leach,
the salts.
Improperly managed
irrigation, especially in arid
and semiarid areas, can result
in salinization and rising
groundwater tables.
Fig. 6-28. Salt accumulated on soil surface and base of plants.
Salinization

HUMAN ACTIVITIES AFFECTING
SOIL DEGRADATION
Human activities can accelerate erosion, acidification,
desertification, and salinization beyond natural rates on a
global scale.

The effects of tree loss
on soil are significant.
Trees and shrubs can
shield the ground from
the force of raindrops, so
the removal of this
vegetation can expose
soil to rain splash. This
loosens soil and
dislodges soil particles,
eroding soil and create a
more impermeable bare
surface, which increases
runoff.
Fig. 6-29(a). Deforested landscape.
Deforestation

Every year, urbanization removes more land from food production, putting more
pressure on the remaining farmland, often in areas with more marginal soil
productivity, to produce more crops and livestock.
Urban and Rural Issues
Image Credit: USDA

Urbanization also
contributes to runoff
and erosion potential
because of the
preponderance of
houses, roads, parking
lots, and other
impermeable surfaces.
When native
landscapes are
converted to urban
uses, runoff increases
several fold.
Urban and Rural
Issues
Image Credit: USDA

Soil loss due to construction
activity is a small fraction of the
whole, but is still a common
occurrence. Construction sites
are often stripped of all
vegetation, leaving bare,
compacted soils with little
infiltration, increasing runoff
and erosion
potential.Regulations and
construction codes now require
mitigation and erosion control
practices to be used.
Fig. 6-33.A silt fence as the only erosion method may fail.
Urban and Rural
Issues

One of the greatest challenges
associated with human,
livestock, and food production
wastes and byproducts is the
quantity of nutrients they
contain. These wastes contain
nutrients that may enter surface
waters through runoff and
erosion or through leaching.
When nutrients get into surface
waters, nutrient overload
(eutrophication) results.
Fig. 6-36. Eutrophication in a small livestock pond.
Land Application of Manures and Treated Wastes

Most meat animals today are
fed in confined animal
feeding operations (CAFOs).
Feed (along with the nutrients
in the feed) are imported
from elsewhere.
Concentrating so many
animals in one place greatly
increases the efficiency of
production.
Image Credit: USDA

In CAFOs, the amount of
manure and effluent (liquid
waste from runoff or washing
production floors) produced
per area increases several fold.
These operations are
considered point sources of
pollution and are regulated
under federal law.
Image Credit: USDA

The wastes contain plant
nutrients and are typically
disposed of through land
application. Increased
nutrient loads in leachates to
groundwater and runoff to
surface waters can result
when the wastes are applied
improperly. When wastes are
applied to the same land over
many years, nutrients may
increase to levels that limit
plant growth.
Image Credit: USDA

Mineland
Reclamation
Fig. 6-37.
Reclamation of the
Standard Mine
Superfund site in
Colorado. The
reclamation activities
involved efforts to avoid
surface and groundwater
contamination,
revegetation, land use
controls to minimize
human exposure to
contaminants and
monitoring.

Historical methods of agricultural production include inverting the soil to bury crop
residues and break up soil aggregates, leaving a bare, uniform surface in which to
plant seeds. Bare soil aggregates are exposed to energy in raindrops and wind,
accelerating erosion. This results in loss of fertile ground, necessitating increased
use of fertilizer to sustain crop yield, which in turn increases cost of food
production.
Agriculture
and Soil
Degradation
Fig. 6-4.
Conventional
inversion tillage.

To control erosion, farmers employ a variety of BMPs: reduced tillage, conservation
tillage, residue management, contour plowing, strip cropping, cover crops, crop rotations,
diversions, terraces, grassed waterways water control structures, and buffer strips.
Agricultural BMPs to Control Erosion
Image Credit: USDA

• Challenges to soil that reduce productivity include:
Erosion, Desertification, Acidification, Salinization.
• Human activities that are degrading the soil are:
Deforestation, Urbanization, Disposal of wastes, Mining
reclamation.
• Best management practices prevent loss of arable soil.
Key Points

Educators PPT file chapter 6

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