What is Soil - Earth and Environmental is Soil Soil is a complex ... Effects of Particle Sizes ... What determines the composition of a soil? Mostly the bedrock, erosion, organic stuff ...
Post on 04-May-2018
What is Soil Soil is a complex mixture of weathered rock, minerals, organic material (both living & decaying), water, and air. Different soils have different amounts. What might change the amounts? On average, soil has the following ratios: 45% minerals & rocks 25% water 25% air 5% organic materialHow is Soil Produced? Weathering of rocks and minerals Deposits of sediments washed/blown to the site Decomposition/actions of living things.Weathering of Rock Weathering is the physical or chemical breakdown of rock into smaller pieces These pieces may be large or too small to see! Two types of weathering: Mechanical ChemicalMechanical Weathering Physical breakdown of rock Chemical composition of the rock does not change Types: Exfoliation Ice Wedging Abrasion Plant & Animal ActivityExfoliation When rocks come to the surface, pressure on them is reduced. This can allow cracks to form, and the rocks break apart. Example: GraniteIce Wedging When water flows into the cracks in rocks & freezes. Why does this split the rocks?Abrasion When rocks broken from other processes collide and break even more. Happens because of gravity, ice, running water, or windwait, how does wind do this?Plant & Animal Activity Plant roots act like ice to split rocks Animals, mostly ones that burrow, expose other rocks for further weathering.Chemical Weathering Chemical reactions break the minerals in the rock into different materials Types: Oxidation Hydrolysis Carbonation Organic Acids Acid RainOxidation When elements in the rock combine with Oxygen, and break off as new compounds. Usually happens in rocks with iron Produces a red colorHydrolysis When chemicals in the rock react with water, causing some of the minerals to break away from the rock. Often happens with metals like Potassium & AluminumCarbonation When CO2 gets into water it makes Carbonic Acid This acid can stick to some minerals and form compounds that are washed away by water. This often happens to limestone.Organic Acids Some living things produce acids that are released to the environment. These acids can make cracks in rocks and start the weathering process. Examples: Lichens & mossesAcid Rain Nitrogen & Phosphorus from fossil fuels get into the air and combine with rainwater This rainwater weathers rock more rapidly than normal rain.Formation of Soil When new rock is exposed, soil begins to form. This newly exposed rock is known as Bedrock.Formation of Soil Weathering begins to break the bedrock into smaller rocks. This layer of partially weathered rocks, above the bedrock, is known as Regolith.Soil Characteristics The size of soil particles also affects the characteristics of a soil. Soils are usually categorized by the amounts of each type of particle that they have. Particles are: Clay: less than 0.0002mm Silt: 0.0002mm 0.05mm Sand: 0.05mm 2mmEffects of Particle Sizes The size of soil particles affects how much water & air the soil can hold. The smaller the particles, the less the soil can hold. However, if the soil is made entirely of larger particles, the water will run right through the soil! We measure particle sizes by measuring Porosity.Porosity:The measure of the volume of pores and distance of poresEffects of Particle Sizes Infiltration: the rate at which water from precipitation or other sources flows into the soilSaturation:The amount of water and air that can move through soilWater WaterHigh permeability Low permeabilitySoil Profiles The formation of soil in different areas produces different layers. These layers are called Horizons. The composition and depth of horizons is measured by looking at a Soil Profile.Soil HorizonsO horizonLeaf litterA horizonTopsoilB horizonSubsoilC horizonParentmaterialMature soilYoung soilRegolithImmature soilWhat changes a Soil Profile? What determines the composition of a soil? Mostly the bedrock, erosion, & organic stuffbut what determines these?!? Climate! Climate mostly affects the layers of a soil, but not the materials found in the soil. In general, climates that have all 4 seasons have all the layers of soil.Soil Erosion What is erosion? The movement of weathered materials from one location to another. Soisnt this the same as weathering? No! Weathering helps to build soil, soil erosion destroys soil. What Causes Soil Erosion? Wind Gravity Water Glaciers Human Actions can speed up the process!Wind WeatheringWind ErosionGravity WeatheringGravity ErosionWater WeatheringWater ErosionGlacier WeatheringGlacier ErosionHumans & Erosion So, how do humans affect this Soil Erosion thing? Development for housing/buildings Farmingthis is the big oneHumans & Erosion Farming can expose a lot of lose soil to erosion. This soil is the O and A horizonswhy are these important? These contain most of the organic material in the soil, which plants and animals need to survive.Farm ErosionIs Erosion Really a Problem?Areas of serious concernAreas of some concernStable or nonvegetative areasWhat can we do to prevent Erosion?Contour Plowing Hillsides are plowed in curves that follow the shape of the land. Prevents water from flowing straight down.Strip Cropping Crops are planted in alternating bands. This way, the whole area is not filled with row crops that dont cover all the land.Terracing Hills are carved into flat steps. This prevents water from flowing rapidly down the hill.Crop Rotation Planting a crop to harvest 1 year, and one to leave in place the next year. Often combined with strip and contour farming.
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