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Principles of Agricultural Science – Plant
1
2
The Size of the Matter
Unit 2 – Mineral SoilsLesson 2.1 Understanding Soil Properties
Principles of Agricultural Science – Plant
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The Components
Soils have four main components that make up the whole
Minerals, 45%
Organic Matter, 5%
Air, 25%
Water, 25%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1
Soil Parts
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Soil Particles
There are three main sizes of soil particles:
• Sand
• Silt
• Clay
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Sand
• .05 – 2 mm
• Round shape
• Feels gritty
Attributes to Soil
• Adds porosity
• Reduces water holding capacity
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Silt
• .002 - .05 mm
• Round shape – but very small to detect
• Feel smooth but does not stick together very well
Attributes to Soil
• Moderately good for porosity
• Helps water holding capacity
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Clay
• Less than .002 mm• Flat or platy• Sticky when wet – ribbon test
• Bad for porosity• Ties up water so plants can’t use it
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Relative Size of Particles
Sand Silt Clay
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Testing for Particles
Field tests can be done to determine the presence of each particle:
1. Moisten a sample of soil with water in your hand.
2. Break up all clods and add enough water to make a slurry.
3. Rub a thin layer of slurry between your thumb and forefinger to isolate the particles.
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Detection of Particles
• Sand is relatively easy to detect the gritty particles
• Wet silts may seem slick like clay but not sticky
• Conduct a ribbon test to determine how much clay content is present
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The Textural Triangle
The triangle helps you determine
classifications for soil
textures
Huddleston & Kling, 1996
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Loams
Loam that has less than 27% clay is a mixture of sand, silt, and clay.
Loam soils are considered to be the optimal soils for growing plants.
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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.