What is Soil? The 4 Core Fractions

An ideal agricultural or forest soil consists of four balanced components: approximately 45% mineral particles, 5% organic matter, 25% air, and 25% water.

Mineral particles (sand, silt, and clay) come from weathered rocks and glacial deposits. Organic matter consists of decaying leaves, roots, fungi, and worms.

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  45% Minerals: Inorganic weathered rock fragments that provide physical structure and micronutrients.
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  5% Organic Matter: Decaying leaves, twigs, microbes, and dark humus that hold water and fertility.
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  25% Soil Air: Oxygen and carbon dioxide held in pore spaces, essential for root respiration.
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  25% Soil Water: Dissolved nutrient solution that plants absorb through root hairs.

To discover what our local soil is made of, each student group conducts a classic shake-jar sedimentation investigation.

By suspending soil in water and allowing it to settle, gravity separates the particles into distinct layers based on particle size and density.

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  1 Clear Jar with Tight Lid: Recycled peanut butter, pickle, or mason jars (16–24 oz).
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  1 Cup of Local Soil: Sample collected from the Tyonek schoolyard, greenhouse, or forest trail.
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  Clean Tap Water: Enough to fill the jar 3/4 full, plus coffee stirrers or popsicle sticks.
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  Rulers & Science Journal: To measure and sketch layer thickness after settling.

Step 1: Place 1 cup of local soil into your clear jar.

Step 2: Add water until the jar is roughly 3/4 full. Observe immediate bubbling as air escapes from soil pores.

Step 3: Secure the lid tightly! Shake the jar vigorously for a full 60 seconds until all soil clumps are thoroughly dissolved into a murky liquid slurry.

Place the jar on a level shelf and do not touch it! Watch how gravity sorts the particles:

Within 1 minute: Heavy, coarse SAND particles fall directly to the bottom.

Within 2 hours: Medium-sized SILT particles settle into a smooth layer over the sand.

Within 24 hours: Microscopic CLAY particles settle at the top, while light ORGANIC HUMUS floats on the water surface.

Natural soils around Tyonek can be acidic and sandy or dense with glacial silt. To grow massive cabbages, potatoes, and carrots, Tyonek Grown farmers actively build up organic matter.

By adding fish compost, cured seaweed, and leaf mulch, farmers increase soil water-holding capacity and feed billions of beneficial microbes that nourish crops.

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  Compost Addition: Raises organic matter from 2% to over 8% in greenhouse beds.
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  Microbial Boost: Allows village crops to thrive without synthetic petroleum fertilizers.