Soil
Soil Formation
1. The four major components of soil are:
Water (25%)
Air (25%)
Organic matter (6%)
Parent material (44%)
2. Parent material is:
Bedrock which provides mineral content of the soil, Ex:
Sand, silt and clay
• Quartz: SiO2
• Calcite: CaCO3
• Feldspar: KAlSi3O8
• Mica (biotite): K(Mg,Fe)3AlSi3O10(OH)2
3. How is soil made from parent material? Include the role
of weathering and living organisms
• Weathering (physical and chemical) creates small pieces
• Dead organisms- decay and release nutrients and gases
• living organisms also release nutrients and gases
Parent material can be native to the area or transported to
the area by wind, water or a glacier
EX:
Calcareous soils in Miami-Dade County are derived from
Miami limestone. Most of Miami-Dade County, part of
Broward County, and Monroe County (including the Florida
Keys). Broward also has marl and stone sand bedrock
4. Humus is: Organic matter
Dead and decayed organisms, ex plant matter
5. How long does it take to make soil from bare
rock?
10 000 years
Soil Profile
1. Describe the 5 Soil horizons
• O- Organic matter, leaf litter (duff),
dead animals, decomposed litter
• A- Surface soil, decomposed organic
matter and minerals, humus (fertile)
• B- Subsoil, leached nutrients
• C- Parent rock, weathered large
unbroken rocks
• R (Bedrock)- mostly a continuous
mass of hard rock
Soil Texture
1. What is soil texture?
• Proportions of clay, sand and silt
 Particle size
Smallest - clay = less than .002mm
- Silt = .002mm - .05mm
largest - sand = .05mm - 2 mm
2. What is porosity?
• Ability to hold water
3.What is permeability?
• Ability of water to flow through the material (rate)
4. Compare permeability of sand and clay.
Water
• Sand high, clay low
High permeability
Water
Low permeability
5. What is a loam?
• A loam has about = mixtures of clay, sand, silt
and humus - best for growing crops.
6. How can soil texture be determined?
• Determined by particle size and feel
Soil type
1. What are the main Soil types?
There are six main types of soil usually discussed in
agriculture, distinguished by the size of the particle matter
that makes up the soil.
• Sandy (water/minerals easily flow)
• Clay (no drainage)
• Silty (fertile, good drainage)
• Loamy (a mixture of soils)
• Chalky (alkaline)
• Peaty (acidic , undecomposed organic matter)
Table 10-1 p. 216
Texture
Nutrient
Capacity
Infiltration
Water-Holding Aeration
Capacity
Clay
Good
Poor
Good
Poor
Poor
Silt
Medium
Medium
Medium
Medium
Medium
Sand
Poor
Good
Poor
Good
Good
Loam
Medium
Medium
Medium
Medium
Medium
Refer to Fig. 10-15 p. 215
Tilth
Soil Erosion is the process by which soil and rock are
removed from the Earth's surface by wind or water
flow, and transported and deposited in other
locations.
Sheet erosion - surface water peels off fairly
uniform sheets of soil.
Rill erosion - fast flowing rivulets cut
Small channels in soil.
Gully erosion - rivulets join together to
Cut wider, deeper ditches or gullies
Two major impacts- loss of soil fertility and
pollution of near by waters
Causes of soil Degradation
1. Deforestation
No vegetation to hold the
soil, soil is removed, loss of
soil fertility, pollutes and can
silt up rivers, decline in fish,
flooding can worsen
Management: prevent
deforestation, manage forest
harvesting, replant
(a) Selective cutting
(b) Clear-cutting
Clear stream
Muddy
stream
(c) Strip cutting
Uncut
Cut 1 year ago
Dirt road
Cut 3–10 years ago
Uncut
Clear stream
Stepped Art
Fig. 10-6a, p. 219
2. Agriculture
Overgrazing- livestock are grazed on land in an
unsustainable way (poorly managed) which leads to soil
erosion and compaction of soil (due to the feet of the
animals)
• Solutions-Rotational grazing- land is not grazed on until
the plants have had enough time to grow back, cattle
supplied with other food sources, ex hay
• Over grazing can lead to desertification
Soils Degradation
 Desertification - combination of
Prolonged drought and human activities
Lead to a reduction in the productive
potential of land.
Solutions: Reduce
1. Overgrazing
2. Deforestation
3. Destructive forms of farming,
irrigation, and mining
Soils: Degradation
 Salinization - salts left on soil as
irrigation water evaporates. Stunts crop
growth and reduces crop yields.
• Waterlogging - farmers leach salts from
Soils by applying large amounts of water.
if water does not drain, saline water sits in pools
and damages roots of plants.
Solution- Drip irrigation, better drainage
Prevention
Reduce irrigation
Switch to salttolerant crops
(such as barley,
cotton, sugar beet)
Cleanup
Flushing soil
(expensive and
wastes water)
Not growing crops
for 2-5 years
Installing underground drainage
systems (expensive)
Preventing and cleaning up soil
salinization
Industrialized Crop Production Causes Soil
Erosion
• Industrialized agriculture, high-input agriculture
(intensive) produces 80% of world’s food supply
• Uses heavy equipment and large amounts of fossil
fuels, water, commercial fertilizers, pesticides, and
financial capital.
• Primarily monocultures – single crop in one area.
– Goal is to steadily increase crop yield, Ex Corn
Reduce Soil Erosion Due to Agriculture
Soil conservation methods
• Crop rotation- Crop rotation is the practice of planting
different crops during consecutive growing seasons. By
doing this the following benefits are applied to the soil
and plants:
• Strip cropping with cover crop
Terracing:
Carving steep hills into terraces
to retain water at each level
and prevent soil erosion
from downhill runoff.
Contour farming: plowing
rows to follow the curve of
gently sloping land. Same
benefits as terracing.
Terracing
Alley cropping: rows of
crops are planted between a
row of trees that provide
fruit or fuelwood and reduce
Evaporation and wind blown
soil erosion
Windbreaks - use rows of
trees to reduce wind erosion
and help retain soil
moisture.
Soil Degradation: conventional tillage
 Conventional-tillage - fields often
Plowed in the fall and left bare over
winter. This leaves it vulnerable to
Erosion, breaks soil structure
Solution: Conservation tillage
Idea is to disturb the soil as little as possible when
planting crops
No-tillage- leave last years crop, use
Seed injectors
Minimum tillage - subsurface soil is
loosened but not topsoil.
CONSERVATON TILLAGE
Advantages
Disadvantages
Reduces erosion
Saves fuel
Cuts costs
Holds more soil water
Reduces soil compaction
Allows several crops
per season
Does not reduce crop
yields
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
• Water Management
Over-watering a crop area will result in erosion of
soil and possible flooded fields.
• To counteract this farmers can plant crops native to
the area that do not require external irrigation or
employ minimal water techniques, such as dripirrigation - the process of only watering the crops
themselves by using a hose with small holes at each
crop.
Case Studies
MEDC- USA pg 303 textbook (Dustbowel 1930s)
LEDC- India see article
Types of Soil
Characteristics
Podzols are soils with an ash• Cool moist environment
grey subsurface horizon,
bleached by organic acids, on Climate:
top of a dark accumulation • Evergreen so limited litter
layer
horizon with brown or black
reddish iron compounds.
• Slow to decompose due to
• Podzols occur in the Boreal limited soil organisms (cold)
and Temperate Zones
Water:
• Soils are acidic (pine
• Lots of water, snow melt
needles), little ground
• Water infiltrates through
vegetation
layers, leaches out nutrients
• Sandy not good for farming (Fe, Al) that collect lower
down the profile.
 Soil horizons
 Soil profile
Immature soil
O horizon
Leaf litter
A horizon
Topsoil
Regolith
Bedrock
B horizon
Subsoil
C horizon
Young soil
Parent
material
Mature soil