2The Formation of Soil What is Soil? Mixture of weathered rock, decayed organic matter, mineral fragments, water, and air.
3Formation of Soil How does soil form? Weathering breaks down rocks and minerals into fragments.Plants and animals add organic material to the soil.May take thousands of years to form.May range in thickness from a few centimeters to 60 meters thick.
4Composition of Soil Rock and Mineral Fragments Mostly small particles of sediment such as clay, silt, and sand.Some larger rocks can be present.
5Composition of Soil Organic Material Dead and Decaying Plants Make up the majority of organic material.Leaves, stems, roots, etc.Dead and decaying animals and microorganisms
6Composition of Soil Organic Material Humus Dark colored material formed from decayed plants and animals.Decay process is due to bacteria and fungi in the soil.Serves as a nutrient source for plants.Mixed with other components of soil by burrowing rodents, worms, and insects.Good-quality surface soil has about 50% humus.
7Composition of Soil Water and Air Fill the spaces between the particles of soil.
8Soil Profile Horizons Different layers of soil. Typical soils have an A, B, and C horizon.All the horizons form a soil profile.
9Soil Profile A Horizon Top layer of soil. Also known as topsoil. Contains a higher percentage of humus.Generally dark and fertile.May be covered with litter.Litter consists of leaves, twigs, and other organic material.Helps prevent erosion and holds water.
10Soil ProfileB HorizonContains material moved down from the A horizon through leaching.Leaching is the removal of minerals that have been dissolved in water.
11Soil Profile C Horizon Consists of partially weathered rock. Coarser than other horizons.Contains less humus.Similar to the parent rock found beneath the horizon.
12Soil Types What affects formation of soil and soil type? Glaciation ClimateType of parent rockType of vegetationSlopeTime
13Soil Types Glacial Deposits Unsorted mass of clay, silt, sand, and boulders.Creates very fertile soil.
14Soil Types Climate Desert soils Prairie soils Temperate Forest soils Contain little organic material.Thinner than soils in wet climatesPrairie soilsThick, dark A horizons due to the large number of grasses.Temperate Forest soilsThinner A and B horizons enriched in minerals due to leaching.
15Soil Types Parent rock Affects the type of soil that develops. Can also affect the vegetation that grows in the area.
16Soil Types Slope Steep slopes Bottomland Soil horizons are often poorly developed.BottomlandSoils are often thick, dark, and full of organic material.
17Soil TypesTimeAt first, soil characteristics are determined by the characteristics of the parent rock.Over time, soil resembles the parent rock less and less.