Geology: Soils Earth Science Prairie School Chapter 14.3 and 14.4
Erosion and Weathering: REVIEW • Erosion:process by which material is dissolved, loosened or worn away from one part of the earth’s surface and deposited in other places. • Mechanical weathering:Large rock mass is broken into smaller fragments of the original material. Ex. Frost wedging, plant/human interactions • Chemical weathering:one or more chemical reactions decompose a mass of rock usually reaction with O2, CO2, and water.
Minerals and Rocks REVIEW • Mineral (diamond, bauxite):element or inorganic compound that occurs naturally and is solid. Rock Types: Rocks are any material that make up a large, natural, continuous part of the earth’s crust. May contain one or more minerals. • Igneous (granite, lava) • Sedimentary (limestone, sandstone) • Metamorphic (marble, slate)
Soils: Formation • Soil: a complex mixture of eroded rock mineral nutrients, decaying organic matter, water, air and billions of living organisms, mostly of the microscopic decomposers. • Soil Composition: Characteristics of the soil depend on the characteristics of the “parent rock” it is formed from. The soil forms distinct layers over time, creating a soil profile.
Soils: Formation • Soil horizons: mature soil is arranged in a series of zones called soil horizons. Each has a very distinct texture and composition that varies with different types of soils. • Soil profile: cross sectional view of the horizons in a soil. Most mature soils have at least 3 horizons of the possible horizons. • OABC Layers
Soils: Formation • Soil Horizon O: Surface litter layer, consists mostly of freshly fallen and partially decomposed leaves, twigs, animal waste, fungi and other organic materials. • Soil horizon A: Topsoil layer, a porous mixture of partially decomposed organic matter called humus. Animals that live in the soil inhabit this layer. Usually darker and looser than deeper layers. A fertile soil will have a thick topsoil with lots of humus. • B and C horizons: inorganic matter and broken-down rock. Layer C is partially weathered bedrock.
Immature soil O Horizon Organic A horizon Topsoil Regolith B horizon Subsoil Bedrock C horizon Parent material Mature soil
Soil Properties • Infiltration: When water percolates downward through the soil through the pores. • Leaching: During the percolation the water dissolves various soil components in the upper layers and carries them to the lower layers.
Soil Properties • Texture: the relative amounts and types of mineral particles. (clay, silt, sand, and gravel) • Loams:are a roughly equal mixture of all the above. • Structure: ways soil particles are organized and clumped together.
Soil Properties • Porosity: determined by soil texture, it measures the volume of pores or spaces per volume of soil and the average distances between those spaces. • Permeability: the rate at which water an d air move from upper to lower soil layers. Influenced by the average size of the pores and the soil structure. • pH: Measures alkalinity or acidity of soil and influences the uptake of nutrients by plants. To correct soil that is too acidic, add lime. When too alkaline add sulfur.
Soil Profiles for Different Biomes • Climate determines the weathering processes and because of this soil formation. • Tropical Soils: lots of rain and high temperatures lead to chemical weathering, developing thick soils rapidly. Contain iron and aluminum, which do not dissolve easily. Lots of leaching of top soil from heavy rains lead to thin A horizon. • Form Thick, Infertile Soils
Soil Profiles for Different Biomes 2. Temperate Soils: Where there is some rainfall and temperatures range from hot to cold, there is both mechanical and physical weathering. These areas have the thickest A horizon. Form Thick, Fertile Soil 3. Desert/Arctic Soils: Little hummus in soil, as it is too cold to sustain life. There is also a very thin layer of mostly regolith from mechanical weathering. Form Thin Soil
Water Water High permeability Low permeability
Soil and Topography The shape of the land has an impact on soil formation. Because water washes away much of the topsoil on a slope, the most fertile soil will be at the bottom of the slope. Lack on vegetation on slopes leads to a low production of organic matter, which forms humus. A flat area, with good drainage, provides the best service for fertile layers of soil.
Homework: Read over Chapter 14.3 by tomorrow Answer Questions 1-9 for the Section 3 Review DUE MONDAY Vocabulary Quiz Tuesday
Soils: Erosion • Sheet erosion: occurs when water moves down a slope or across a field in a wide flow and peels off fairly uniform sheets or layers of soil. • Rill erosion: occurs when surface water forms fast-flowing rivulets that cut small channels in the soil. • Gully erosion: when rivulets of fast-flowing water join together and with each succeeding rain cut the channels wider. See Fig. 10-18 p. 217
How Serious Is the Problem of Soil Erosion? • Causes loss of soil organic matter and vital plant nutrients • Reduced ability to store water for use by crops • Increased use of costly fertilizer to maintain soil fertility • Increased water runoff on eroded mountain slopes that can flood agricultural land and dwellings in the valleys below • Increased buildup of soil sediment in waterways and coastal areas that reduce fish production and harms other aquatic life • Increased input of sediment into reservoirs
Areas of serious concern Areas of some concern Stable or nonvegetative areas Global Soil Erosion Fig. 10-19 p. 218
Soil Erosion in the U.S. • Erosion in the U.S. has been a major concern for years as the farmers plowed over the fields every year at harvest and left it bare for a long period of time allowing it to be eroded mainly by wind. • Since the great Dust Bowl of the 1930’s, caused by a severe drought and over-plowing for years, the development of the Soil Conservation Service ahs made the prevention of soil erosion their top priority. (now known as the National Resources Conservation Service)
Waterlogging: Large amounts of irrigation water are used to leach salts deeper into the soil. However many times the soil doesn’t have good drainage and there is an accumulation of water as the water table rises. The roots get enveloped in water and lower their productivity and killing them after prolonged exposure. Evaporation Evaporation Transpiration Waterlogging Less permeable clay layer Fig. 10-22 p. 221
Solutions: Soil Conservation • Soil Conservation:reducing soil erosion and restoring soil fertility. Most often done by keeping the soil covered. • Conventional-tillage:Soil is plowed in the fall and left bare through winter and early spring and vulnerable to erosion • Conservation tillage: disturb soil as little as possible while planting crops. Minimum tillage and no-till farmingallow for the land to remain with crops residues and cover vegetation without disturbing the topsoil.
Solutions: Soil Conservation • Cropping methods: various cropping methods are used to reduce erosion, largely by working with the land and protecting the removal of topsoil. Include: terracing, contour planting, strip cropping, alley cropping, windbreaks, and gully reclamation. • Land Classification:classify the land to identify whether it is suitable for cultivation.
Soil Restoration • Organic fertilizer:plant and animal waste • Animal manure:from cow, goat ,chicken, horses, etc. • Green manure:from plant wastes • Compost:sweet dark brown humus like material rich in organic matter. • Spores:spores that attach to roots to help absorb nutrients • Crop rotation:rotate crops that deplete soil with those that conserve and add nutrients to the soil
Commercial inorganic fertilizer : contain nitrogen, phosphorous and potassium. They may contain trace amounts of other required nutrients. Easily transported, stored and applied. Used extensively worldwide. • Problems: • They don’t add humus to the soil • Reduce soil organic matter and ability to hold water • Lowers oxygen content and ability to take up nutrients • Not all nutrients needed are included • Lots of energy needed for production, transport and application • Increase global warming by release of N2O