Transcript Structure and Depth Perception

Principles of Agricultural Science – Plant
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Principles of Agricultural Science – Plant
Structure and Depth Perception
Unit 2 – Mineral Soils
Lesson 2.1 Understanding Soil Properties
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Soil Structure
When soil particles cling together in an
arrangement known as a ped, it is called
structure.
Two considerations must be made for soil
structure:
• Structure type
• Structure grade
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Structure Type
The shape of the ped formed is called
structure type.
Granular – roughly spherical, like grape nuts.
Usually 1-10 mm in diameter. Most common in A
horizons, where plant roots, microorganisms, and
sticky products of organic matter decomposition
bind soil grains into granular aggregates.
Platy – flat peds that lie horizontally in the soil.
(Huddleston & Kling, 1996)
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More Defined Structure Types
Blocky – roughly cube-shaped, with more or less
flat surfaces. If edges remain sharp, it is called
angular blocky. If the edges are rounded, the peds
are called subangular blocky. Blocky structures are
typical of B horizons.
Prismatic – larger, vertically elongated blocks,
often with five sides.
(Huddleston & Kling, 1996)
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Structureless Types
Massive – compact, coherent soil not separated
into peds of any kind. Massive structures in clayey
soils usually have very small pores, slow
permeability, and poor aeration.
Single grain – in very sandy soils, every grain acts
independently, and there is no binding agent to
hold the grains together into peds. Permeability is
rapid.
• The above structure types are the two
extremes in terms of effects on permeability.
• Neither present great conditions for crop use.
(Huddleston & Kling, 1996)
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Structure Grade
How strongly the ped is held together is
structure grade.
Four grades define soils:
• Strong
• Moderate
• Weak
• Structureless
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Effects of Structure
Good structure, or strong structure, means
good aeration because of ample pore
space.
Organic matter is important for forming soil
structure.
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Effective Depth
Relative to structure is soil evaluation criteria
called effective depth.
Effective depth is the zone, which plant roots
can easily grow.
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Limitations of Effective Depth
Barriers for root growth are caused by:
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Massive soils
Dense soil structure
Poor internal drainage
Abrupt texture changes between horizons
Gravelly and large sands
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Signs of Promise for Roots
Good conditions for effective depth include:
• Moderate and strong structure grades
• Brown or red soils, which indicate good
aeration
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References
Huddleston, J. H., & Kling, G. F. (1996). Manual
for judging Oregon soils. Corvallis, OR: Oregon
State University.
Parker, R. (2010). Plant and soil science:
Fundamentals and applications. Clifton Park,
NY: Delmar.
Plaster, E. J. (2003). Soil science & management
(4th ed.). Clifton Park, NY: Delmar.
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