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Soil is a mixture of weathered rock and organic matter

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Presentation on theme: "Soil is a mixture of weathered rock and organic matter"— Presentation transcript:

1 Soil is a mixture of weathered rock and organic matter
Soil is a mixture of weathered rock and organic matter. It also contains mineral fragments, water, and air.

2 Soil Formation Soil starts as weathered rock. Plants grow in weathered rock. Worms, insects, bacteria and fungus live among the plant roots and help soil evolve by adding organic matter.

3 Humus Humus is dark-colored organic matter made of pieces of decaying plants and animals Worms and insects mix the humus with the fragments of rock.

4 Soil Profiles AB&C Horizon
The O horizon is filled with organic matter (leaf litter). The A horizon, known as topsoil, it is the most fully evolved layer in a soil profile. It is dark & contains more humus & smaller sediments.

5 B - Horizon The B layer is lighter in color & contains little or no humus & contains minerals that were washed down (leaching) from the topsoil.

6 C-Horizon & Below The C horizon is the bottom layer in a soil profile, it contains partly weathered rock, but no humus. Below the C-horizon is parent rock.

7 Types of Soil The thickness of the horizons & the soil composition depend on many conditions. Rate of weathering Hot & Moist = increased chemical weathering & more vegetation Cool & Moist = increased mechanical weathering Climate (humidity and temperature) The type of rock the soil has evolved from. Slope of the land & the amount of humus in the soil. Grassland vs. Mountain slope

8 Soil Loss Desertification or desert formation
occur where soils are damaged by overgrazing & poor farming practices in areas that receive little or no rain. Overgrazing strips plants from the land. This results in erosion of topsoil & slows soil evolution.

9 The Dust Bowl In the 1930s, the “Dust Bowl” was created by poor farming practices, overgrazing, & a drought in the Great Plains. It caused soil to be carried away by water & wind, creating dust storms and widespread famine.

10 Overgrazing in the Tropics creates Desertification
Deforestation, clear-cutting, and slash & burn farming removes all trees & many nutrients, it also gives a very short growing period before the existing nutrients in the soil are used up.

11 Preventing Soil Loss Crop rotation – Rotating crops so nutrients are not used up. Cover crops - Keeps soil in place. Barriers – reduce wind and water erosion

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