Understanding Soil Composition: A Guide to Texture and Structure

1. Characteristics of Soil 5.2 Soil Soil is part of the regolith that supports the growth of plants. • Regolith is the layer of rock and mineral fragments that covers most of Earth’s land surface.

2. Characteristics of Soil 5.2 Soil Soil Composition • Soil has four major components: mineral matter, or broken-down rock; humus, which is the decayed remains of organisms; water; and air.

3. Composition by Volume of Good-Quality Soil

4. Characteristics of Soil 5.2 Soil Soil Texture • Texture refers to the proportions of different particle sizes. - Sand (large size) - Silt - Clay (small size) • Loam (a mixture of all three sizes) is best suited for plant life.

5. Characteristics of Soil 5.2 Soil Soil Texture (SAND) -Sand has less nutrients for plants than smaller particles -Voids between sand particles promote free drainage and entry of air -Holds little water and prone to drought

6. Characteristics of Soil 5.2 Soil • Soil Texture (SILT) • -Smaller particles – retains more water for plants and have slower drainage than sand. • -Easily washed away by flowing water – highly erosive. • -Holds more plant nutrients than sand.

7. Characteristics of Soil 5.2 Soil • Soil Texture (CLAY) • -Pores spaces are very small and convoluted • Movement of water and air very slow • -Water holding capacity • Tremendous capacity to adsorb water- not all available for plants. • -Chemical adsorption is large

8. Characteristics of Soil • Soil Consistence • -Loose: the soil breaks apart when held • Friable: the soil breaks apart with a • small amount of force • -Firm: the soil breaks apart with a lot of • pressure between two fingers 5.2 Soil

9. Characteristics of Soil 5.2 Soil Soil Structure • Soil particles clump together to give a soil its structure.

10. Humus/Organic Matter Humus/Organic Matter • Organic matter is made up of: • Decomposing Plants Such as leaves and flowers AND -Decomposing animals Such as insects • Organic Matter breaks down into nutrients which are used by plants for growth. Organic matter is made up of: • Decomposing Plants Such as leaves and flowers AND • Decomposing animals Such as insects • Organic Matter breaks down into nutrients which are used by plants for growth.

11. Soil Formation 5.2 Soil The most important factors in soil formation are parent material, time, climate, and organisms. 1.Parent material • Residual soil—parent material is the bedrock • Transported soil—parent material has been carried from elsewhere and deposited

12. Soil Formation 5.2 Soil 2. Time • Important in all geologic processes • The longer a soil has been forming, the thicker it becomes. 3. Climate • Greatest effect on soil formation

13. Soil Formation 5.2 Soil 4. Organisms • Organisms influence the soil's physical and chemical properties. • Furnish organic matter to soil

14. The Soil Profile 5.2 Soil Soil varies in composition, texture, structure, and color at different depths. Soil horizons are zones or layers of soil. A soil profile is a vertical section through all the soil horizons. • The A horizon is commonly know as topsoil. • The B horizon is subsoil and contains clay particles washed out from the A horizon. • The C horizon is between B horizon and unaltered parent material.

15. Soil Profile

16. A Soil Profile Showing Different Horizons

17. Soil Erosion 5.2 Soil Water erodes soil. Rates of Erosion • Human activities that remove natural vegetation, such as farming, logging, and construction, have greatly accelerated erosion.

18. Soil Erosion 5.2 Soil Controlling Erosion • Planting rows of trees called windbreaks • Terracing hillsides • Plowing along the contours of hills • Rotating crops