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Soils
Chapter 5
SOIL
• Is the soft material that covers the
surface of the earth and provides a
place for the growth of plant roots.
• It also contains minerals, organic
matter, air, and water.
Parent Material
Igneous rocks – heat created from deep in the
earth. Granite, quartz
Sedimentary rocks – formed by moving
particles (wind water and glacial) and then
recombining. Limestone, sandstone
Metamorphic – rocks that have changed due to
high pressure and or high heat. Marble and
slate
Formation of Soil
(weathering)
• Water
– Movement
– Freezing
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Wind
Glacial
Chemical
Temperature
Mechanical
– Roots, earthquakes, landslides
Five factors control soil formation
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Parent material
Time
Climate
Vegetation
Topography
Composition of soil.
5%
20-30%
Water
Air
45%
Mineral
20-30%
O.M.
Soil Textures
is the amount of sand, silt and clay in the soil.
Clay – fine and plat like, holds a tremendous
amount of water and nutrients poor
drainage. Smallest
Silt – in between particle between clay and
sand. Medium.
Sand – excellent drainage, warms up quickly
in the Spring, poor water retention and
fertility. Largest.
Texture Triangle
Soil Profile
• Refers to the arrangement and
properties of the various soil layers.
• Top soil
• Sub soil
• Parent Material
Soil Horizons
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O Horizon
A Horizon
B Horizon
C Horizon
• Depth & Colors
Soil Water Relationship
• Why is water needed in the soil?
– Movement of minerals into the plant
– Movement of glucose
– Photosynthesis
– Cooling
• Water types
– Gravitational water
– Capillary water
– Hygroscopic water
– Crystal lattice water
Soil Water Relationship cont.
1) Hygroscopic Water is held so strongly by
the soil particles (adhesion), that it is not
available to the plants
2) Capillary Water is held by cohesive forces
greater than gravity and is available to
plants
3) Gravitational Water is that water which
cannot be held against gravity
– as water is pulled down through the soil,
nutrients are "leached" out of the soil (nitrogen)
Saturation Percentage
• Immediately following an irrigation, the
film of water is thick, and smaller pores
are full of water. The soil particles can
not hold the water. It is easily lost to
the plant.
• 1/10 Atmosphere (Near Saturation)
What is Field Capacity?
• when the soil contains the maximum
amount of available water, the greatest
amount of water it can hold against
gravity.
• 1/3 Atmosphere
• ½ saturation %
What is Permanent
Wilting Point?
• the soil has so little water, that plants
can no longer recover from wilting.
• roots can no longer take in water.
• 15 Atmospheres.
• ¼ Saturation %
What is Available Water?
• the amount of water between field
capacity and wilting point
Chemical Properties
• Soil pH
– The amount of hydrogen ions in the soil.
• Soil pH range is 0 to 14.
• Acid soil is soil with a pH below a 7
-Probably high rainfall and possibly high
in organic matter.
-Use lime to raise pH
-Many fertilizers have an acid affect on
the soil.
pH cont.
• Alkaline soil is that which is above a
pH of 7
-Low rainfall areas
-Use sulfur to lower pH
• Neutral at a pH of 7
-Gypsum acts a buffering agent
Cation Exchange Capacity
Used to determine fertilization schedules
• Sodic and Saline Soils – High amounts
of sodium with a pH of 8.5 or above.
• Saline-sodic Soils = same as Sodic but
with a pH of 8.4 or below.
Organic Matter
• Improves physical condition &
structure.
• Increase water infiltration.
• Decrease erosion losses.
• Supply plant nutrients.
• Micro-Organisms enrich the soil.
Soil Classification
• Why classify soil?
• How can it help you?
Soil Management
• Erosion
– Sheet & Rill
– Gully
• Conservation
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Contour Cropping
Strip cropping
Terraces
Grass Waterways
Conservation Tillage
• No-Till
• Minimal Till
• Ridge Planting System
Soil Compaction
• What is soil compaction?
Soil Compaction
• How do we prevent soil compaction?
• How do we repair soil that is
compacted?