Download Ch.13 - HCC Learning Web

Chapter 13: Soil and Its Uses
 13.1 The Study of Soil as a Science
 13.2 Geologic Processes
 13.3 Soil and Land
 13.4 Soil Formation
 13.5 Soil Properties
 13.6 Soil Profile
 13.7 Soil Erosion
 13.8 Soil Conservation Practices
 13.9 Conventional Versus Conservation Tillage
 13.10 Protecting Soil on Nonfarm Land
13.1 The Study of Soil as a Science
 Soil science
Is the study of soil as a natural resource on the surface
of the earth including soil formation, classification and
mapping; physical, chemical, biological, and fertility
properties of soils; and these properties in relation to
the use and management of soils.
13.2 Geologic Processes
 The crust of the Earth is an extremely thin, less-dense





solid covering over the mantle.
The mantle makes up the majority of the Earth, and
surrounds a small core of iron.
The outermost portion of the mantle is solid.
The crust and solid outer mantle are collectively known
as the lithosphere.
The asthenosphere is a thin layer below the outer
mantle capable of plastic flow.
The core consists primarily of iron and nickel and has
a solid center and a liquid outer region.
Geology
Structure of the Earth
Plate tectonics
 Plate tectonics is the concept that the outer surface of
the Earth is made of large plates of crust and outer
mantle (lithosphere) that are slowly moving over the
surface of the liquid outer mantle.





Heat from the Earth causes the slow movement of the outer
layer.
Plates are pulling apart in some areas, and colliding in others.
liquid mantle moves up and solidifies. Thus, new crust is
formed (half of the surface of the Earth have been formed in
this way, such as the bottom of the Atlantic Ocean).
Where plates collide, often one plate slides under the other and
is melted (volcanoes and mountains are formed, such as in the
west coast of America).
When two continental plates collide, the crust buckles to form
mountains (The Himalayan, Alp, and Appalachian mountain
ranges).
Tectonic plates
Weathering
 Weathering processes are important in reducing the size
of particles that can then be dislodged by moving water and
air.
 Mechanical weathering results from physical forces that
reduce the size of rock particles without changing the
chemical nature of the rock.
Freezing and thawing cycles
 Heating a large rock can cause it to fracture
 Glaciers cause rock particles to grind against one another, resulting
in smaller fragments.
 Actions of plants (roots) and the burrows of animals
 Wind and moving water remove small particles and deposit them at
new locations, exposing new surfaces to the weathering process.

Chemical weathering
 Chemical weathering involves the chemical
alteration of rock in such a manner that it is more
likely to fragment or be dissolved.
 The process of loosening and redistributing
particles is called erosion.
13.3 Soil and Land
 Land is the portion of world not covered by water.
 Soil is a mixture of minerals, organic material, living
organisms, air, and water that together support
growth of plant life.

Good agricultural soil:
 45% Mineral
 25% Air
 25% Water
 5% Organic Matter
This combination provides good drainage,
aeration, and organic matter.
The components of soil
13.4 Soil Formation
 Soil forming factors include the following:
 Parent
Material
 Climate
 Topography
 Biological Factors
 Time (it takes about 500 years to form 1 inch of
soil in dry or cold climates)
Biological factors
 The first organisms to gain a foothold in modified
parent material also contribute to soil formation.
Decomposition of dead further alters underlying rock.
 Animals and microorganisms mix soils and form burrows
and pores.
 Plant roots open channels in the soil.

Humus
 Humus is the organic material resulting from the decay of
plant and animal remains.


It mixes with top layers of mineral particles, and supplies needed
nutrients to plants.
It creates a crumbly soil that allows adequate water absorption and
drainage.
 Burrowing animals such as earthworms bring nutrients up
from deeper soil layers, improving soil fertility.
 Dry or cold climates develop soils very slowly, while humid
and warm climates develop them more rapidly.
 Cold and dry climates have slow rates of accumulation of
organic matter.
 Chemical weathering proceeds more slowly at lower
temperatures and in the absence of water.
13.5 Soil Properties
 Soil texture is determined by the size of mineral
particles within the soil.
 Too many large particles, such as gravel (larger
than 2 millimeters in diameter) and sand
(between 2 mm and 0.05 mm) lead to extreme
leaching (carrying dissolved organic matter and
minerals to lower layers).
 Too many small particles, such as silt (0.05 mm
to 0.002 mm) and clay (less than 0.002 mm)
lead to poor drainage.
Soil Properties
 Soil structure refers to the way various soil
particles clump together.
 Particles in sandy soil do not attach to one another
(granular structure). Particles in clay soil tend to
stick to one another to form large aggregates.
In good soils, one-half to two-thirds of spaces contain air
after excess water has drained.
 A good soil is friable, which means that it crumbles
easily.
 Protozoa, nematodes (wireworms), earthworms, insects,
algae, bacteria, and fungi are typical inhabitants of soil.

13.6 Soil Profile
 The soil profile is a series of horizontal layers of
different chemical composition, physical properties,
particle size, and amount of organic matter.
 Each recognizable layer of the profile is known as a
horizon.
Soil Profile
 A horizon is the topsoil, or the uppermost layer. It contains





most of the soil nutrients, small mineral particles, and living
organisms (dark color).
O horizon is made of litter (undecomposed or partially
decomposed organic material). Forest soils have an O horizon.
E horizon is formed from leaching darker materials (from A).
Usually very nutrient poor.
B horizon is the subsoil. It contains less organic matter and
fewer organisms, but accumulates nutrients leached from
topsoil. It supports a well-developed root systems. Soils in
woodlands that receive high rainfall have B horizon.
C horizon is weathered parent material below the subsoil. It
has no organic materials.
R horizon is bedrock (limestone, granite, etc).
Soil Profile
13.7 Soil Erosion
 Erosion is the wearing away and transportation of soil
by wind, water, or ice.
 Worldwide, erosion removes 25.4 billion metric tons of
soil per year.


Made worse by deforestation and desertification.
Poor agricultural practices increase erosion and lead to the transport
of associated fertilizers and pesticides.
 Most current agricultural practices lose soil faster than it
can be replenished.
 Wind erosion may not be as evident as water erosion, but
is still serious.


It is most common in dry, treeless areas.
Great Plains of North America have had four serious bouts of wind
erosion since European settlement in the 1800s.
13.8 Soil Conservation Practices
 When topsoil is lost, fertility is reduced or destroyed,
thus fertilizers must be used to restore fertility.
This practice raises food costs, and increases sediment
load in waterways.
 Over 20% of U.S. land is suitable for agriculture, but only
2% does not require some form of soil conservation
practice.

Soil Conservation Practices
 Agricultural Potential
 Worldwide:
11% of land surface is suitable for crops.
 An additional 24% is in permanent pasture.


United States:
20% land surface suitable for crops.
 25% in permanent pasture.


African Continent:
6% land surface suitable for crops.
 29% can be used for pasture.

Soil Conservation Practices
 Soil Quality Management Components:
 Enhance organic matter.
 Avoid excessive tillage.
 Manage pests and nutrients efficiently.
 Prevent soil compaction.
 Keep the ground covered.
 Diversify cropping systems.
Soil Conservation Practices
 Contour farming is tilling at right angles to the
slope of the land. Each ridge acts as a small dam.


Useful on gentle slopes.
One of the simplest methods for preventing soil erosion.
 Strip farming is the practice of alternating strips of
closely sown crops (hay, wheat) with strips of row
crops (corn, cotton, soybeans) to slow water flow,
and increase water absorption.
Soil Conservation Practices
 Terracing is the
practice of constructing
level areas at right angles
to the slope to retain
water.

Good for very steep land.
Terraces
Soil Conservation Practices
 Waterways are depressions in sloping land where
water collects and flows off the land.

Channels movement of water.
 Windbreaks are plantings of trees or other plants
that protect bare soil from full force of the wind.

Windbreaks reduce wind velocity, decreasing the amount of
soil that can be carried.
13.9 Conventional Versus Conservation Tillage
 Plowing has multiple desirable effects:
 Weeds and weed seeds are buried.
 Crop residue is turned under, where it will contribute to soil
structure.
 Leached nutrients brought to surface.
 Cooler, darker soil brought to top and warmed.
Conventional Versus Conservation Tillage
Reduced tillage is a practice that uses less
cultivation to control weeds and prepare soil, but
generally leaves 15-30% of soil surface covered with
crop residue after planting.
Conventional Versus Conservation Tillage
 Conservation tillage further reduces amount of
soil disturbance and leaves 30% or more of soil
surface covered with crop residue.




Mulch tillage: Tilling entire surface just prior to planting.
Strip tillage: Tilling narrow strips that will receive seeds.
Ridge tillage: Leaves ridges; the crop is planted on the ridge
with residue left between ridges.
No till farming: Involves special planters that place seeds in
slits cut in the soil.
Conventional Versus Conservation Tillage
 Positive Effects of Reduced Tillage:
 Wildlife gain winter food and cover.
 Less runoff results in reduced siltation of waterways.
 Row crops can be planted in sloped areas.
 Fewer trips over the field means lower fuel consumption.
 Two crops may be grown on a field in areas that had been
restricted to a single crop.
 Fewer trips over the soil means less soil compaction.
Conventional Versus Conservation Tillage
 Drawbacks of Conservation Tillage
 Plant residue may delay soil warming.
 Crop residue reduces evaporation and upward movement of
water through the soil, which may retard the growth of plants.
 Accumulation of plant residue can harbor plant pests and
diseases, requiring more insecticides and fungicides.