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 FormationSoil 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 HumusHumus is dark-colored organic matter made of pieces of decaying plants and animalsWorms 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 - HorizonThe B layer is lighter in color & contains little or no humus & contains minerals that were washed down (leaching) from the topsoil.
6 C-Horizon & BelowThe 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 SoilThe thickness of the horizons & the soil composition depend on many conditions.Rate of weatheringHot & Moist = increased chemical weathering & more vegetationCool & Moist = increased mechanical weatheringClimate (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 BowlIn 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 LossCrop rotation – Rotating crops so nutrients are not used up.Cover crops -Keeps soil inplace.Barriers –reduce wind andwater erosion