Soil Regolith – layer of rock and mineral fragments produced by weathering Soil – part of regolith that supports plant growth

Soil Composition Mineral matter, humus (decayed, organic material), air, water

Soil Texture Texture refers to % of particle sizes Sand (large size) Silt Clay (small size) Loam (a mixture of all three sizes) is best suited for plant life

Soil Texture

Soil Formation The most important factors in soil formation are: parent material time climate organisms slope

Soil Formation: Parent Material Residual soil: parent material is the bedrock Transported soil: parent material has been carried from elsewhere and deposited

Soil Formation: Time • The longer a soil has been forming, the thicker it becomes

Soil Formation: Climate Greatest affect on soil formation hot/wet – thick/chemically weathered soil cold/dry – thin/mechanically weathered soil

Soil Formation: Organisms plants – main source of organic matter, acids from decay increase weathering animals – burrow and mix materials (earthworms)

Soil Formation: Slope steep – more erosion = thin/nonexistent soil flat – little erosion = thick soils

Soil Profile A Horizon – (topsoil) B Horizon – (subsoil) C Horizon - mixture of mineral and organic matter, insects, fungi, microorganisms  B Horizon – (subsoil) fine clay particles leached out of A horizon  C Horizon - partially weathered parent rock