Transcript Conserving Land and Soil

Conserving Land and Soil
Types of Land Use
• Agriculture
– New farmland must be
created by clearing
forests, draining
wetlands, and
irrigating deserts.
Types of Land Use
• Development
– Every year in the US,
about a million
hectares of farmland
are developed.
– Reduces the amount
of farmland and
destroys wildlife
habitats.
Types of Land Use
• Mining
– Strip mining removes
nonrenewable
resources from the
land.
• Expose the soil and
causes erosion.
– In underground
mining, minerals are
carried up through
shafts of tunnels that
have been dug out.
Restoring the Land
• It is possible to
restore land damaged
by erosion or mining.
(land reclamation)
• In some cases,
subsoil and topsoil
are replaced and
grass is planted so
that the area can be
used as agricultural
land.
Protecting the Soil
• Erosion
– Plant roots usually hold soil in place.
– Many uses of land expose the soil and can
cause erosion
• logging
• mining
• farming
Protecting the Soil
• Desertification
– The advance of
desertlike conditions
into areas that
previously were fertile
• Climate (drought)
• Overgrazing of
grasslands by cattle
and sheep
• Poor farming practices
and excessive cutting of
trees for firewood
Protecting the Soil
• Nutrient Depletion
– If farmers plant the same crops in a field year
after year, nutrients are used faster than
decomposers can replace them.
– Prevention
• Periodically leave fields fallow
• Leave the unused parts of crops in the fields rather
than clearing them away.
• Crop rotation
The Nitrogen Cycle
• The process by which nitrogen is removed
from the atmosphere, fixed in the soil by
bacteria, incorporated in other living
things, and then released back into the
atmosphere.
The Nitrogen Cycle
• Nitrogen Fixation
– The process of changing free nitrogen gas
into a usable form of nitrogen
– Done by bacteria, some of which live in
bumps called nodules on the roots of certain
plants (legumes)
• Clover, beans, peas, alfalfa, and peanuts
The Nitrogen Cycle
• Return of Nitrogen to the Environment
– Once the nitrogen is fixed into complex
compounds, it can be used by organisms to
build proteins and other substances.
– Decomposers break down these complex
compounds in wastes and dead organisms
and return nitrogen compounds in the soil.
– At some time, the bacteria completely break
down the compounds and release free
nitrogen back into the air.
The Nitrogen Cycle