3.4 The Soil System

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Transcript 3.4 The Soil System

Soil is a complex mixture of eroded rock,
mineral nutrients, decaying organic matter,
water, air and billions of living organisms
(microscopic decomposers).
1.
2.
3.
Weathering of rock (mechanical).
Deposition of sediments by erosion
(mechanical).
Decomposition of organic matter in dead
organisms (chemical).
“O” HORIZON = freshly fallen and partially
decomposed leaves, twigs, animal waste. You
can find fungi and other organic materials.
“A” HORIZON = porous mixture of partially
decomposed organic matter (humus) and some
inorganic mineral particles.
These top two layers are most fertile, have the
highest concentration of organic matter, and
contain large amounts of living organisms.
Rove beetle
Flatworm
Adult
fly
Pseudoscorpion
Centipede
Ant
Fly
larvae
Millipede
Sowbug
Roundworms
Beetle
Protozoa
Slug
Snail
Mite
Springtail
Bacteria
Fungi
Mite
Earthworm
Ground
beetle
Mite
Organic debris
Actinomycetes
“B” (subsoil) and “C” (parent material)
HORIZON contain most of the soil’s
inorganic matter, broken-down rock.
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Clay (very fine particles)
Silt (fine particles)
Sand (medium-size particles)
Gravel (coarse to very coarse particles)
SOIL TEXTURE is determined by the relative amounts of the
different types and sizes of mineral particles.
100%clay
0
clay
80
60
Increasing
percentage clay
40
clay
loam
sandy clay
loam
20
0
100%sand
loamy
sand
80
Increasing
percentage silt
silty
clay
sandy
clay
40
sand
20
silty clay
loam
loam
sandy
loam
60
80
silty
loam
silt
60
40
Increasing percentage sand
20
100%silt
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Soil texture helps determine SOIL POROSITY, a
measure of the volume of spores or spaces per
volume of soil and the average space between
those spaces.
INFILTRATION is the downward movement of
water through soils.
As the water seeps down, it dissolves various
soil components in upper layers and carries
them down to lower layers in a process called
LEACHING.
Water
High permeability
Water
Low
permeability
Properties of Soils with Different Textures
Texture
Nutrient
Capacity
Infiltration
WaterHolding
Capacity
Aeration
Workability
Clay
Good
Poor
Good
Poor
Poor
Silt
Medium
Medium
Medium
Medium
Medium
Sand
Poor
Good
Poor
Good
Good
Loam
Medium
Medium
Medium
Medium
medium
Nitrogen fixing
by lightning
Pathway of
plant
nutrients in
soil.
Commercial
inorganic
fertilizer
Organic fertilizers,
animal manure,
green manure, compost
Crop
plant
10-6-4
N-P-K
Dead
organic matter
Application
to land
Nitrogen fixing
Decomposition
Supply of
available plant
nutrients in soil
Weathering
of rock
Nitrogen fixing
by bacteria
Nutrient removal
with harvest
Absorption of nutrients
by roots
Nutrient loss
by bacterial
processes
such as
conversion
of nitrates to
nitrogen gas
Nutrient loss
from soil erosion
Soil erosion is the movement of soil components,
especially surface litter and topsoil.
 The two main agents of erosion are wind and
flowing water.
 Loss of plant cover by farming, logging,
construction, overgrazing by livestock, off-road
vehicles, deliberate burning of vegetation and
other activities leave soil vulnerable to erosion.
Two major harmful effects of soil erosion:
1.
2.
Loss of soil fertility and its ability to hold water
Runoff of sediment that pollutes water, kills fish
and shellfish, and clog irrigation ditches, boat
channels, reservoirs, and lakes.
serious concern
some concern
Stable areas
Causes
Consequences
Overgrazing
Worsening drought
Deforestation
Famine
Surface mining
Economic losses
Erosion
Lower living
standards
Salinization
Soil compaction
Environmental
refugees
SALINATION
WATERLOGGING
1. Irrigation water
contains small
amounts of dissolved
salts.
• Precipitation and
irrigation water
percolate
downward.
2. Evaporation and
transpiration leave
salts behind.
• Water table
rises.
3. Salt builds up in soil.
Both result in stunted plant growth,
lower crop yields,
dead plants and ruined land.
Transpiration
Evaporation
Evaporation
Evaporation
Waterlogging
Less permeable
clay layer
Advantages and disadvantages of using
Conservation Tillage.
Advantages
Reduces erosion
Saves fuel
Cuts costs
Holds more soil water
Reduces soil compaction
Allows several crops
per season
Does not reduce crop
yields
Disadvantages
Can increase herbicide
use for some crops
Leaves stalks that can
harbor crop pests and
fungal diseases and
increase pesticide use
Requires investment
in expensive equipment
Contour planting and strip cropping: each row acts
as a small dam to help hold soil and slow water
runoff.
Alley cropping or agroforestry: several crops are planted
together in strips or alleys between trees and shrubs that can
provide fruit or fuel-wood, shade, help retain and slowly
release soil moisture, and fodder for livestock.
Windbreaks or shelterbelts of trees reduce wind erosion, help
retain soil, supply wood for fuel, and provide habitats for birds,
pest-eating and pollinating insects, and other animals.
Terracing retains water
for crops at each level
and reduces soil erosion
by controlling runoff.
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Organic fertilizer
Manure
Compost crop rotation
No till farming
Contour farming
Terracing
Nitrogen fixation-legumes