Introduction to Agriculture, Food, and Natural
Resources
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Introduction to Agriculture, Food, and Natural
Resources
What’s in Soil?
Unit 3 – Lesson 3.3 Starting from the
Ground Up
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Soil is…
• The mineral and organic surface of
the earth capable of supporting
upland plants.
• Formed by the environment breaking
down parent material over time.
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Soil Components
Soil Components
Soils are made of four main components.
25%
45%
Minerals
Organic Matter
Air
Water
25%
5%
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Mineral Matter
• Includes rock and mineral fragments.
• Fragments are classified by size.
Gravel
Sand
Silt
Clay
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Organic Matter
Organic Matter includes things, such as:
• Plant roots
• Decaying leaves and other vegetative
parts
• Animals:
– Microorganisms (i.e., nematodes and fungi)
– Insects (i.e., larva and worms)
– Small mammals (i.e., gophers and moles)
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Air
• Air provides oxygen for plant roots.
• Soil air is trapped in pores of the soil.
• Porosity is a term to define how much
open space is available for air and water
to be held in the soil.
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Water
• Pore space in the soil can also be filled by
water.
• Some soil water is available for plant use.
• Organic matter can hold more water
because it creates pores and may even
absorb water like a sponge.
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Water
• If a soil has too many or large pores,
water drains away and is not held for
plant use.
• If a soil has no pores, the water does
not filter through the soil and erosion
can occur.
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References
Parker, R. (2010). Plant and soil science:
Fundamentals and applications. Clifton
Park, NY: Delmar.
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