protecting soil from erosion project.ppt

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
PowerPoint® Slides prepared by
Jay Withgott and Heidi Marcum
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Ch 9
Soil and Agriculture
Part 2: Environmental Issues
and the Search for Solutions

This lecture will help you understand:
• The relationship between
soils and agriculture
• Major agricultural
developments
• The fundamentals of soil
science
• Causes and consequences
of soil erosion and
degradation
• Principles of soil
conservation

Soil as a system
• Soil consists of mineral
matter, organic matter,
air, and water
- Dead and living
microorganisms, and
decaying material
- Bacteria, algae,
earthworms, insects,
mammals,
amphibians, and
reptiles
Since soil is composed of living and non-living matter, it is
considered an ecosystem

Soil formation is slow and complex
• Parent material = the base material of soil (solid rock)
• Weathering = the physical, chemical, or biological
processes that break down rocks to form soil
- Physical (mechanical) = wind and rain, no chemical
changes in the parent material
- Chemical = substances chemically interact with
parent material
- Biological = organisms break down parent material

Weathering produces soil

Other processes affect soil formation
• Biological activity such as decomposition accumulates
organic matter
• Humus = a dark, spongy, crumbly mass of material rich
in nutrients

A soil profile consists of horizons
• Horizon = each layer of soil
• Soil profile = the cross-section
of soil as a whole
• Up to six major horizons may
occur in a soil profile
- Topsoil = inorganic and
organic material most
nutritive for plants
- Leaching = dissolved
particles move down through
horizons

O Horizon: Litter layer
Consists mostly of organic matter
A Horizon: Top Soil
Organic material mixed with minerals
E Horizon: Leaching Layer
Minerals and organics are washed out
B Horizon: Subsoil
Accumulate of organics and minerals
C Horizon: Weathered parent material
Parent material that has been altered
R Horizon: Parent Material
Rock that soil is formed from

Soils are characterized in many ways
• Soils are classified based on color, texture, structure, and pH
• Soil color = Color of the soil
indicates its composition and fertility
- Black or dark brown = rich in organic matter
- Pale gray or white = indicates leaching (removal of nutrients)
• Soil texture = determined by the size of particles
Particle size determines how easy it is to cultivate and let air
and water travel through the soil
- From smallest to largest = clay, silt, sand
- Loam = soil with an even mixture of the three

Which soil color is best for agriculture?
Darker = nutrient rich

What particles make up the BEST soil
Clay, Silt, or Sand?

Particle Size
Name Particle
diameter
Sand 0.05-2.0 mm
Silt 0.002- 0.05 mm
clay Less than 0.002

Water Holding Capacity
• Should retain water for plant growth
• During heavy rains, if water is not absorbed
water can pool and take a long time to drain or
run off resulting in flooding
• Most important factor: Spaces of air between
the soil particles
• Water Holding Capacity depends on infiltration
rate and capillary action

Infiltration Rate
• Gravitational flow through soil
• Soils with high infiltration rate are easily leached
(removing nutrients)

Capillary Action
• Strong attraction between water molecules and soil
causes water to be drawn upward from the water
table.
• Capillary action increases when soil is packed close
enough to provide a continuous film of surface
• Soils with high rate of capillary action lose water
more quickly through evaporation than soil where
capillary action is slower.

Ions
What do ions do for plants?
• Nitrogen: gives plants green color
• Phosphorous: helps seed production
• Potassium: gives fruit color, helps with fruit
production

Soil texture classification
Silty soils with medium-size
pores, or loamy soils with
mixtures of pore sizes are
best for plant growth and
crop agriculture

pH Scale

Soil pH
• Soil pH = influences a soil’s ability to support plant
growth (plants grow best at pH of 7)
- Soils that are too acidic or basic can kill plants
- When pH gets too low, soil can not bond to nutrients

Soil structure
• Soil structure = a measure of soil’s “clumpiness”
- Large clumps can discourage plant roots

Population and consumption degrades soil
• Feeding the world’s rising human population requires
changing our diet or increasing agricultural production
• Land suitable for farming is running out
• We must find ways to improve the efficiency of food
production
• Mismanaged agriculture turns grasslands into deserts;
removes forests; diminishes biodiversity; and pollutes
soil, air, and water
- Fertile soil is blown and washed away

Millions of acres of cropland are lost each
year
We lose 5-7 million ha (12-17 million acres) of
productive cropland annually

Soil degradation has many causes
• Soil degradation results from
erosion, and
salinization/desertification

Plant cover reduces erosion

Types of erosion
1. Splash erosion: water impacts surface loosening and
breaking up soil particles
2. Sheet Erosion: rainfall intensity of a storm exceeds the
infiltration capacity of the soil
3. Rill Erosion: is caused by water concentrating into
closely closely-spaced areas forming small channels
4. Gully Erosion: steep-sided trenches formed by rill
erosion

Various types of soil erosion
Splash
Sheet
Rill
Gully

Soil erodes by several methods
• Rill erosion moves the most topsoil, followed by sheet
and splash forms of erosion
Despite conservation measures, the U.S. still loses 6 tons of soil
for every ton of grain harvested

Erosion degrades ecosystems and
agriculture
• Deposition = the arrival of eroded material at its new
location
• Flowing water deposits sediment in river valleys and
deltas
• But, erosion is a problem because it occurs faster than
new soil is formed
• Erosion increases through: excessive tilling, overgrazing,
and clearing forests

Overgrazing causes soil degradation
• Overgrazing = too many
animals eat too much of the
plant cover
- Impedes plant regrowth
• A leading cause of soil
degradation
70% of the world’s rangeland is classified as degraded

Effects of overgrazing can be striking
• Weeds invade grazed land
- Less nutritious to livestock
- Out compete native vegetation
Ungrazed plot Grazed plot

Forestry impacts soil
• Clear-cutting = the removal of
all trees from an area at once
- Leads to soil erosion,
especially on steep slopes

Tilling the land

Irrigation: boosted productivity, but
problems, too
• Irrigation = Artificially providing
water to support agriculture
• Waterlogging = over-irrigated
soils
- Water suffocates roots
• Salinization = the buildup of salts
in surface soil layers
- Worse in arid areas
Salinization inhibits production of 20% of all irrigated cropland,
costing more than $11 billion/year

Salinization prevention
• Do not plant water-guzzling
crops in sensitive areas
• Irrigate with low-salt water
• Drip irrigation targets
water directly to plants

Desertification
• Desertification = a process
by which fertile land turns
into barren land
• Causes: Erosion, soil
compaction, forest removal,
overgrazing, salinization,
climate change, depletion of
water sources
• Most prone areas = arid and
semiarid lands

Dust Bowl

Fertilizers boost yields but cause problems
• Fertilizer = substances that contain essential nutrients
• Inorganic fertilizers = mined or synthetically manufactured
mineral supplements
• Organic fertilizers = the remains or wastes of organisms
- manure, crop residues, fresh vegetation
- Compost = produced when decomposers break down
organic matter to produce humus
Applying
synthetic
fertilizer, vs.
Planting rye,
a “green
manure”

Overapplication of Fertilizer

Environmental effects of over-fertilizing

Protecting soil: crop rotation and contour
farming
• Crop Rotation = alternating the
crops grown field from one
season or year to the next
• Cover crops protect soil when
main crops aren’t planted
- Wheat or corn and soybeans
• Contour Farming = plowing
furrows sideways across a
hillside, perpendicular to its
slope, to prevent rills and gullies

Protecting soil: terracing and intercropping
• Terracing = level platforms
are cut into steep hillsides,
sometimes with raised edges
- A “staircase” to contain
water
• Intercropping = planting
different types of crops in
alternating bands or other
spatially mixed arrangements
- Increases ground cover

Protecting soil: shelterbelts
• Shelterbelts = rows of trees or
other tall, perennial plants that are
planted along the edges of fields to
slow the wind
• Reduced Tillage = furrows are cut
in the soil, a seed is dropped in and
the furrow is closed
- No-till farming disturbs the soil
even less

QUESTION: Review
Traditional subsistence agriculture uses all of the following,
except:
a) Animal power
b) Irrigation
c) Irrigation water
d) Fossil fuels

QUESTION: Review
Physical weathering is characterized by:
a) The chemical interaction of water with parent
material
b) Organisms breaking down parent material
c) Wind or rain breaking down parent material
d) The dislodging or movement of soil by wind

QUESTION: Review
Which horizon is the most valuable for agriculture?
a) Topsoil (A horizon)
b) E horizon
c) B horizon
d) R horizon

QUESTION: Review
Erosion increases through all of the following, except:
a) Excessive tilling
b) Overgrazing
c) Clearing forests
d) All of the above increase erosion

QUESTION: Review
Which sustainable farming method involves planting rows
of trees along field edges to slow the wind?
a) Terracing
b) Crop rotation
c) Shelterbelts
d) Contour farming

QUESTION: Weighing the Issues
Should developed nations fund reforestation projects in
developing nations to combat erosion and deforestation?
a) Absolutely, developing nations are facing a crisis
b) No, not with money, but developed nations could
give advice
c) No, developed nations had to solve their problems,
let the others solve their own problems
d) I don’t care, it doesn’t really affect me

QUESTION: Weighing the Issues
Should the U.S. government provide farmers with financial
incentives to use technologies such as no-till farming
and crop rotation?
a) Absolutely, farmers may be more likely to switch to
these techniques
b) Yes, but farmers must put any money received into
the farm
c) No, it’s not the government’s job to interfere with
farming practices
d) I don’t care, it doesn’t really affect me

QUESTION: Interpreting Graphs and Data
According to this figure, which of the following is NOT true?
a) Reduced tillage
results in less nitrogen
loss
b) Conventional tillage
causes more soil loss
c) Organic carbon lost
is greater with reduced
tillage
d) Conventional and
reduced tillage have few
differences

protecting soil from erosion project.ppt

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