Soils and EnvironmentSoil is important in:Land capability: suitability of land for a particular useWaste-disposal problems—interaction btwn waste, water, soil and rock determine suitability of particular site to receive wasteCan help evaluate natural hazards—landslides, floods, earthquakesCarry a climatic signal—indicates what past climate was likeWeathering: physical and chemical breakdown of rocks and first step in soil developmentResidual soil: weathered material that remains essentially in place on bedrockTransported soil: eroded rock particles that are transported by water, wind or glaciers and then modified in their new deposition locationSoil horizons:Vertical and horizontal mvmts on material in a soil system create a distinct layering, parallel to the surface, collectively called a soil profileLayers are called zones or soil horizonsLook at pg. 530 for diagram of layers and zonesO Horizon: mostly composed of organic materials including decomposed or decomposing leaves, twigs etc.A horizon: composed of both mineral and organic materials. Leaching: process of dissolving, washing or draining Earth materials by percolation of groundwater or other liquids, occurs in the A horizon and moves clay and other material such as iron and calcium to B horizonE horizon: composed of light-colored materials resulting from leaching of clay, calcium, magnesium and iron to lower horizons. A and E horizons together constitute zone of leachingB horizon: enriched in clay, iron oxides, silica, carbonate or other material leached from overlying horizons. Horizon is known as the one of accumulationC horizon: composed of partially altered aren’t material; rock is shown here but material could also be alluvial in nature, such as river gravels in other environment. Horizon may be stained red with iron oxidesR: unweathered parent materialHardpan: hard compacted soil horizonSoil properties:Color:O and A horizons tend to be dark bc of abundant organic materialE horizon may be almost whiteB horizon shows most dramatic differences depending on presence of clay minerals and iron oxidesBk horizons may be light=colored bc of carbonates, but sometimes reddishTrue K horizon, may be almost whiteColor indicates how well a soil drainsTexture:Depend on relative proportions of sand, silt and clay sized particlesStructureSoil particles cling together in aggregates called peds that are classified according to shapeGranular: A horizonBlocky: B horizonPrismatic: B horizonPlaty: E horizonLook at pg. 533Soil FertilityIn every cubic meter has small rodents, insects, worms, algae, fungi and bacteriaRefers to the capacity of soils to supply nutrients, such as nitrogen, phosphorus and potassium needed for plant growthSoil developed on flood planes or similar places contain sufficient nutrientsSoils from highly leached bedrock or on loose deposits have little nutrients and organic materialDevelopment and maintenance of many terrestrial ecosystems depend upon soilChemical weathering releases chemicals that can be used by the organisms in the soilWater in soilSoil is composed of bits of solid material and organic matter with pore spaces in btwn that are filled with gas or waterSoil classificationSoil taxonomyClassification of soil for agricultural and land-useEngineering classificationsUnified soil classification systemEngineering properties of soilsLook at table pg. 535Soil strengthAbility of soil to resist deformationCohesion; measure of ability of very small silt and clay soil particles to stick togetherCan depend on size of granulesVegetation can play a role in soil strengthSoil sensitivityMeasures changes in soil strength resulting from disturbances such as vibrations or excavationsSoil compressibilityMeasure of a soil’s tendency to consolidate, or decrease in volumeErodibilityEase with which soil materials can be removed by wind or waterHydraulic conductivityMeasure of ease with which water moves through a materialCorrosion potentialSlow weathering or chemical decomposition that proceeds from surface into groundEase of excavationPertains to procedures and equipment required to remove soil during constructionEarth mover, back hoe…Rippable excavationBlasting, rock cuttingShrink-swell potentialTendency of a soil to gain or lose water.Soils that tend to increase or decrease in volume with water content are called expansive soilsCan cause environmental problems, such as changing the shape of the ground a house is built onRates of soil erosionMeasured as volume, mass or weight of soilSediment pollutionChokes streams, fills lakes, reservoirs, ponds, canals, drainage ditches and harborsBuries vegetationLand use and environmental problems of soilsAgricultureA lot of damage over the years to agricultureWays to reduce damage, erosion:Contour plowing: plowing the with natural topography of the landNo-till agriculture: eliminates plowing altogether, greatly reducing soil erosionTerracing slopes: produce flat areas for farming. Stone or other materials are used to form terracesPlanting more than one crop: allows the land to recover since not always using the same resources—best in small farms in tropical rain forestUrbanizationConversion of agricultural, forested or rural landAffects soil by:May be scraped off and lost so they may have lower strengths when they are remoldedMaterials may be brought in from outside areas to fill a depression before construction, resulting in a much diff soil than was previously thereDraining soils to remove water may cause dessication, or drying out, and other changes in soil propertiesSoils in urban areas are susceptible to soil pollution resulting from deliberate or inadvertent addition of chemicals to soilsOff-Road vehiclesCause soil erosion, changes in hydrology and damage to plants and animalsSoil pollutionOccurs when materials detrimental to people and other living things are inadvertently or deliberately applied to soilsSoil surveys and land-use planningShould include soil descriptions, soil maps showing the horizontal and vertical extent of soils and results of test to determine grain size, moisture content and strengthCh. 16 Outline 20/10/2010 05:31:00← Soils and Environment- Soil is important in:oLand capability: suitability of land for a particular useoWaste-disposal problems—interaction btwn waste, water, soil and rock determine suitability of particular site to receive wasteoCan help evaluate natural hazards—landslides, floods, earthquakesoCarry a climatic