3G Science - Soils

3 Layers of Soil

• Topsoil – top layer of soil. Has the smallest grains. Most humus. Richest layer of soil.

• Subsoil – Under the topsoil. Larger grains than the topsoil. Less humus.

• Bedrock – Solid rock under the subsoil. Weathering breaks down bedrock into soil. Bedrock is made of different minerals in different places, so soils in different places contain different minerals.

Parts of Soil

• Weathered rock• Humus – decomposed plant and animal parts• Air• Water

Types of Soil

• Clay – smallest grains, packed tightly with little room for air, holds water easily, sticky when wet, stays stuck together when dry. May have gray, orange or red color.

• Sand – larger grains, loosely packed, has large spaces for lots of air, drains water quickly, falls apart when dry. Light in color.

• Loam – mixture of clay, sand and humus. Best soil for growing plants. Clay helps it to retain water, sand allows soil to stay loose which provides room for air. Humus adds nutrients, making the soil rich. Dark or black in color.

• Mineral – a solid formed in nature which has never been alive. Metals, rocks, crystals