Transcript Soils and Fertilizers

Soils
Plant Material Maintenance
Soil

Soil is the top layer of the Earth’s crust.
 Millions
of years to make
 Being lost at a rate of 5.2 tons/acre/year (Iowa statewide average)
Pore Space
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Two kinds:
 Macro
pore space
 Micro pore space
air
water
The Ideal Soil
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In undisturbed soils organic matter helps
bind soil particles into larger aggregates.
Soil Horizons and the Soil
Profile:
O – Thin layer of decomposing organic matter.
A – Primarily composed of inorganic materials
(sands, silts, and clays) it is also normally rich in
organic matter. This horizon has a characteristic
dark color.
E – Not present in all soils and not pictured in the
illustration to the left.
B – Zone of accumulation where materials that have
leached from the surface mix with soil particles
from the lower parent material.
C – Composed of partially weathered parent
material.
Inorganic (Mineral) Soil Particles
Sand
 Silt
 Clay
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Properties of sand, silt, and clay:
Size
Shape
Water
Infiltration
Aeration
WaterHolding
Capacity
NutrientHolding
Capacity
Sand
Largest
2.0 – 0.05mm
Naked eye
Round
or
angular
Rapid
Good
Low
Low
Silt
Medium
0.05 – 0.002mm
Microscope
Round
or
angular
Slow
Poor
Moderate
Moderate
Clay
Smallest
<0.002mm
Electron
microscope
Waferlike
Moderate
to poor
Moderate High
to poor
High
Water-holding Capacity
Soils with a large percentage of
micropores have a high water-holding
capacity - clay
 Soils with a larger percentage of
macropores over micropores have a lower
water-holding capacity - sand
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Gravitational Water

Water that drains from the
macropores under the force
of gravity after a
rain/irrigation event.
Field Capacity
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A soil is said to be at field
capacity immediately after
the gravitational water has
drained away.
Water that remains held in
the micropores is called
capillary water.
 available
 unavailable
Permanent Wilting Point

When available water is
depleted, and no additional
water is added, plants may
reach the permanent wilting
point.
Soil Texture
Determined by the percentages of sand,
silt, and clay a soil contains.
 Textural triangle.

Loam Soils
Ideal balance of 3 particles
 Results in high fertility and good water
retention
 Drains well
 Desired for gardening
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Organic Matter (OM)
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Generally only present in very small quantities;
5% or less.
Most OM in the form of humus: stable,
decomposed plant and animal life.
 In
sandy soils - increases water and nutrient holding
capacity.
 In clay soils - improves drainage, air movement, and
helps form aggregates.
Cation-Exchange Capacity
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Capacity of a soil to attract and hold nutrients on
the surface of soil particles.
Soil and organic matter have negative charges.
Nutrients have positive charge, so are attracted
to the negative charges .
Clay soils and soils high in organic matter have
higher CEC rates.
pH Scale
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Measures the acidity/alkalinity.
pH affects the nutrient availability in the soil.
Ranges from 0 to 14. pH of 7 is neutral.
Less than 7 is acidic.
More than 7 is alkaline.
pH of 6 is 10 times more acidic than 7 pH.
pH of 5 is 100 times more acidic than 7 pH.
Nutrient availability and pH
At certain pH levels, some micronutrients
become unavailable to the plant. They
become chemically bound to the soil
particles.
 pH level of 6.5-7.0 is the optimal range for
most micronutrients.
 Iron is commonly deficient due to high pH
soil.
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Adjusting pH levels
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Low pH soils (acidic)
 Add
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lime
High pH soils (alkaline)
 Very
difficult to lower pH on large scale
 Add sulfur
 Add organic amendments
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Oak leaves, sphagnum moss, pine needles
Mychorrhizal Fungi
A symbiotic relationship between plant
roots and fungi.
 The fungi help roots absorb water and
nutrients.
 The roots provide the fungi with food
(sugar).
 Most plants growing in “undisturbed” soils
have mychorrhizal fungi growing in
association with their roots.
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End