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Published byAshley Holmes Modified over 8 years ago
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Introduction to Soils Compliments of: Elizabeth Sulzman OSU Soil Science James Cassidy OSU Soil Science Teresa Matteson Benton SWCD Heath Keirstead Benton SWCD
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Soil is … Absolutely crucial for life on Earth! www.pikeconservati on.org/SoilEcosyste m.htm
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5 functions of soil Soil anchors and provides nutrients for plants. Some animals live in soil; it is a habitat. Soil recycles waste through decomposition. Soil cleans and stores water. Soil has engineering uses.
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The five factors of soil formation Climate Organisms Topography/relief Parent Material Time Soil = f(cl,o,r,p,t) Passive Factors Active Factors
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Missoula Floods delivered parent material to Willamette Valley
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Landscape positions
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Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock Soil O horizon: organic matter, plant and animal litter A horizon: topmost mineral horizon, darker than B horizon B horizon: mineral horizon: zone of accumulation C horizon: weathering soil; little organic matter or life R horizon: unweathered parent material; rock
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Minerals Organic matter Water Air Soil has four components
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The four components of soil:
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Mineral component Makes up less than 50% of a “soil” Varies in chemical composition Contains particles of several size ranges (small to really really small) Depends on the underlying geology/bedrock
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Organic matter Small constituent by weight, but huge influence on soil properties Made up of partially decomposed plant & animal residues + organic compounds synthesized by soil microbes O ni
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Functions of Organic Matter 1. Stabilizes soil structure, making soil easily managed 2. Increases the amount of water a soil can hold (and availability of the water) 3. Major source of plant nutrients 4. Main food/energy for soil organisms
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Soil Water Held to varying degrees depending on amount of water and texture of soil Not all soil water is available to plants
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Soil Air 1. High spatial variability 2. High temporal variability 3. High moisture content (Rh 100%) 4. High CO 2 content 5. Low O 2 content
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Soil Physical Properties Color Texture Structure Aggregate stability
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Soil Color Moisture Mineralogy (calcite, hematite, manganese) Coatings on particles: O.M. darkens underlying colors Fe and Al oxides (red & yellow)
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Texture – Proportions of sand, silt, and clay Determines water holding capacity, water availability, nutrient supply capacity… Loam is a soil texture with optimal sand, silt and clay contents for growing plants. Clay is a soil particle size and a soil texture.
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% clay % silt % sand
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“Big” smaller really small Sand silt clay Relative Size Comparison of Soil Particles (fine earth fraction)
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Sand Clay Fine clay has ~10,000 times as much surface area as the same weight of medium grain sand!
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Coarse textured soils larger pores Fine textured soils greater total pore space Sand Clay
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Clay particle mostly negative charged surface - + - + - + - + Ca ++ - - - - - - - - - - - - - - + - K+K+ NH 4 + Ca ++ - - Fe++
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Influence of Texture SandSiltClay Water-holding capacity Aeration Drainage Nutrient retention LowMediumHigh GoodPoor Medium SlowVery slowHigh LowMedium
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Types of Soil Structure
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Why Are Aggregates Important? Increase porosity Increase water infiltration, drainage, decrease runoff Increase water holding capacity http://www.youtube.com/watch?v=9_ItEhCrLoQ
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Effect of OM on aggregate stability
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Compaction Pore spaces are where plants get air, water, and nutrients. Soil compaction decreases valuable pore space between soil particles. Adapted from Sulzman and Frey, 2003
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Less Greater Compaction
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Take home message Clay soils have a higher water-holding capacity than sandy soils Water in coarse textured soils is easier for plants to remove than in fine textured soils Much of the water in high-clay soils is unavailable to plants, while most water in sandy soils is available
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A cup of soil contains... Bacteria Fungi Protozoa Nematodes Arthropods Earthworms 200 billion 100,000 meters 20 million 100,000 50,000 <1 The immobile ones all primarily found in the rhizosphere, the zone of soil closest to plant roots
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Bacteria
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Nematodes Protozoa
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Mites Springtails
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Other invertebrates
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Worms Voles! Ant Colony!
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Aggregates held together by: –Fungal hyphae –Bacterial “glues” –Organic matter sand silt hyphae clay bacteria
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Amoebae Ciliate Flagellate Nematode feed on bacteria and fungi release plant nutrients – protozoa KEY for N Nematode Microfauna
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Collembola (springtails) Fungus feeding mite feed on fungi, protozoa, nematodes, mites important in regulating populations of everything smaller Nematode feeding mite Mesofauna
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Photo by Suzanne Paisley shred plant material feed on bacteria and fungi associated with organic matter Macrofauna
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Earthworms Important component of soil fauna (not in acid soils, not in very dry soils) Pass as much as 30 tons/ha of soil through their bodies each year Casts (poop) are higher in N, P, K, Ca, Mg, pH, and CEC than soil Promote good soil structure and aeration
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Earthworm casts vs. soil CharacteristicEarthworm castsSoils % silt & clay22.2 Structural stability65 CEC (cmol c /kg)3.5 38.8 849 13.8
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Nitrogen Fixation (bacteria) Take N 2 from atmosphere, convert to soil NH 4 + Nodules formed on roots Examples include: –Rhizobia on legumes –Frankia on alder via organic matter N N NH 4 +
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SOIL ORGANIC MATTER Living Organisms: BIOMASS Dead tissues and wastes: DETRITUS Non-living, non-tissue: HUMUS SOM: What it is
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Sand Clay Large surface area means more charge so greater ability to hold water and nutrients
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Set up a soil column to see how soil purifies water. Hands-on FUN!!!
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Back to why we might care… …plants = food
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Erosion: A process that transforms soil into sediment –Natural (soils form over time in most settings) –Human-induced (e.g., over-grazing, forest harvest) Tied with damage to plant communities Wind vs. water (usually 2/3 by water)
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Downward spiral of land degradation
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Three steps of water erosion Most erosion is initiated by the impact of raindrops, NOT by the flow of running water
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Wind erosion 40% of soil transported by erosion in USA In six of the Great Plains states, wind erosion exceeds water erosion Fine particles can even be transported to other continents
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Current problems World population is increasing rapidly Only 10% of the world’s land area is suitable for growing crops Most of the most arable land is already in production Soil quality is degrading world-wide
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The real voyage of discovery consists not in seeking new landscapes but in having new eyes. ~Marcel Proust
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