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Fragile Ecosystem
- upper layers provide nutrients and water to plants
- Plants, bacteria, insects, fungi, nematodes live in and create structures of soil
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Soil Stratification
- -layers known as horizons
- -upper layer is topsoil
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Name soil particles from smallest to largest (3)
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what does topsoil consist of
- mineral particles
- living organisms
- decaying organic material
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Loams
soils that support highly productive plant growth composed of roughly equal parts sand, silt, and clay
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cations adhere to?
negatively charged soil particles
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what happens during cation exchange?
- cations are displaced from soil particles by other cations
- Displaced cations enter the soil solution and can be taken up by plant roots
- Negatively charged ions do not bind with soil particles and can be lost from the soil by leaching
- •Percolating groundwater
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how does agriculture impact soil
- Depletes nutrients
- –Increases erosion
- –Taxes water resources
- –Soil compaction
- –Alters soil communities
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Aquafiers
primary source of irrigation water is in these underground water reserves
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the depleting of aquifiers can result in?
subsidence- the settling or sinking of land
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salinization
- concentration of salts in soil as water evaporates
- irrigation can lead to this
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Fertilization replaces what?
mineral nutrients that have been lost from the soil
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commercial fertilizers are enriched in?
- nitrogen
- phosphorus
- potassium
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organic fertilizers are composed of?
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Large monoculture farms with high fertilizers have?
bacteria dominated soil food webs
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natural systems and organic farms have?
fungal based soil food webs
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what does erosion of soil cause?
loss of nutrients
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how can erosion be reduced
- –Planting trees as windbreaks
- –Terracing hillside crops
- –Cultivating in a contour pattern
- –Practicing no-till agriculture
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when is a chemical element considered an element?
if it is required for a plant to complete its life cycle
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Macronutrients
- 9 essential elements
- -plants require them in large amounts
- Carbon
- Oxygen
- Hydrogen
- Nitrogen
- Phosphorus
- Sulfur
- Potassium
- Calcium
- Magnesium
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Micronutrients
- 8 elements
- plants need them in small amounts
- Chlorine
- Iron
- Manganese
- Boron
- Zinc
- Copper
- Nickle
- Molybdenum
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Rhizosphere
- •The layer of soil bound to the plant’s roots
- •The rhizosphere has high microbial activity because of sugars, amino acids, and organic acids secreted by roots
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Rhizobacteria
- •Free-living
- •Function in the rhizosphere
- •Can enter roots
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what can rhizobacteria do
- –Produce hormones that stimulate plant growth
- –Produce antibiotics that protect roots from disease
- –Absorb toxic metals
- –Make nutrients more available to roots
- •Inoculation of seeds with rhizobacteria can increase crop yields
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Nitrogen cycle
transforms nitrogen and nitrogen-containing compounds
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where does most soil nitrogen come from?
- actions of soil bacteria
- nitrogen can be an important limiting nutrient for plant growth
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what do plants absorb nitrogen as?
either NO3– or NH4+
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Nitrification
carried out by bacteria that convert NH3 into NO3–
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Nitrogen fixation
conversion of nitrogen from N2 to NH3 through nitrogen- fixing bacteria because plants cannot directly take in the N2 from the atmosphere
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plants in legume family have what with nitrogen fixing bacteria
a symbiotic relationship
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nodules
- swellings along legume's roots, composed of plant cells infected by nitrogen fixing rhizobium bacteria
- The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen
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bacteroids
Inside the root nodule, Rhizobium bacteria assume this form called bacteroids, which are contained within vesicles formed by the root cell
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