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soil study guide


what is soil? relatively thin surface layer of the Earth’s crust
What does soil consist of? mineral and organic matter that is affected by agents such as weather, wind, water, and organism
What are the 4 distinct parts of soil? mineral particles, organic matter, water, air
What percent of soil is mineral particles? 45%
What percent of soil is organic matter? 5%
What percent of soil is water? 25%
What percent of soil is air? 25%
Why is soil important to microorganisms? inhabit the soil & depend on it for shelter, food & water
Why is soil important to plants? Plants anchor themselves into the soil, and get their nutrients and water
Why is soil important to terrestrial plants could not survive without soil, therefore, humans could not exist without soil either
Is soil a renewable or nonrenewable resource? Renewable resource
What does soil provide nutrients for? for plant growth and also helps purify water
What is weathering? Soil formation begins when bedrock is broken down by physical, chemical and biological processes
What are mature soils? soils that have developed over a long time
What are soil horizons a series of horizontal layers
How is the parent material of soil formed? The rock that has slowly broken down into smaller particles by biological, chemical, and physical weathering
How long does it take parent material to form? To form 2.5 cm (1 in.) it may take from 200-1000 years
What are examples of physical weathering? Erosion (wind, water, ice, etc)
List some examples of chemical weathering A plant’s roots or animal cells undergo cell respiration and the CO2 produced diffuses into soil, reacts with H2O & forms carbonic acid (H2CO3). This eats parts of the rock away
What produces new soil? decomposition
Where is soil NOT renewable in tropical rainforests
Why isn't soil renewable in tropical rain forests? all of the nutrients are caught in the trees and when cut down & burned the soil cannot get the nutrients back
How do you measure soil with texture The percentages (by weight) of different sized particles of sand, silt and clay that it contains
What is the texture of gravel/stones >2mm in diameter
What is the texture of sand 0.05 to 2mm
Which has the larger soil particles? Sand
What is the soil texture of silt? .002 to .05 mm
What is about the size of flour and barely visible with the eye? Silt
What is the soil texture of clay? <.002mm
Which soil texture has the greatest surface value and can only be seen under an electronic microscope? Clay
Why is gravel/stones not actually considered soil? it doesn’t have direct value to plants
What does it mean if soil is gritty? It has a lot of sand
What does it mean is soil is sticky? high clay content and you should be able to roll it into a clump
What does it mean if soil is smooth, like flour? It is silt
What is the structure of soil? How soil particles are organized and clumped together. (Sand, silt, clay)
What is Friability in soil? How easily the soil can be crumbled
What is the Porosity in soil? A measure of the volume of soil and the average distances between the spaces
What is Permeability in soil The rate at which water and air moves from upper to lower soil layers. It is distances between those spaces
How do soils vary? in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them
What is shrink well potential? Some soils, like clays, swell when H2O gets in them, then they dry and crack. This is bad for house foundations, etc.
What is the pH of most soils? 4.0 to 8.0
What is the pH of the Pygmy Forest in California? extremely acidic with 2.8 to 3.9
What is the pH of Death Valley California? very basic 10.5
Why are plants affected by pH because of the solubility of nutrient minerals
Why do steep slopes have little or no soil on them? because of gravity
What does runoff from precipitation do to a slope? it erodes it
What do moderate slopes and valleys encourage? the formation of deep soils
Where are soils very shallow in texas? San Antonio
Soil depth can range from? 2 inches of soil then rock or 36 inches deep of soil
What does dark soil say? it is rich with lots of organic matter
What does light soil like sand say? not so rich with very little organic matter
What is the uppermost layer of the soil called? O-horizon/Organic Layer
What is the O-horizon/Organic layer rich in? organic material
What accumulates in the O-horizon? plant litter and it gradually decays
When is the O-horizon completely absent? in desert soils
When is the O-horizon a dominant layer? in certain organically rich soils
What is horizon is top soil? A-horizon
What is topsoil/A-horizon? dark and rich in accumulated organic matter and humus
What horizon/layer has a granular texture? Topsoil/A-horizon
Why is topsoil/A-horizon some what nutrient poor? due to the loss of many nutrient minerals to deeper layers and by leaching
Which layer is the B horizon? the sub soil layer
What is subsoil/B-horizon? The light-colored subsoil beneath the A-horizon
Why is subsoil/B-horizon often a zone of illuviation? nutrient minerals have leached out of the topsoil and litter accumulate
Which soil layer is typically rich in iron and aluminum compounds and clay? Subsoil/ B-horizon
Which layer is the C-horizon? Parent Material
What is in the C-horizon/Parent material? contains weathered pieces of rock and borders the unweathered solid parent material
Why is C-horizon/Parent material often saturated with ground water? Most roots do not go down this deep
What happens during Infiltration? the downward movement of water through soil
What happens during Leaching? dissolving of minerals and organic matter in upper layers carrying them to lower layers
What does soil type determine? the degree of infiltration and leaching
What are macronutrients? larger in atomic structure
What are examples of macronutrients? Nitrogen, Phosphorus, Potassium
What are examples of micronutrients? Selenium, Zinc, Iron
What are micronutrients? smaller in atomic structure
What are organic fertilizers? animal manure, crop residues, bone meal, and compost
What are inorganic fertilizers? man-made from chemical compounds
What are benefits of inorganic fertilizers? exact compositions are known; they are soluble & thus immediately available to the plant
What are the costs of inorganic fertilizers? quickly leach away; this pollutes the water; doesn’t help the water holding capacity of the soil like organic fertilizers do
How much soil is eroded in the US each year? 6.4 billion tons
How much would 6.4 billion tons fill up this would fill 320 million average-sized dump trucks that, if parked end-to-end, would extend to the moon and ¾ of the way back
What is erosion the movement of soil components, especially surface litter and topsoil, from one place to another
What do the roots of plants do in undisturbed ecosystems? help anchor the soil
What destroys plant cover and leaves soil vulnerable to erosion? farming, logging, construction, overgrazing by livestock, off-road vehicles, deliberate burning of vegetation
Destroying soil in a few decades ruins solid that took how long to produce? what nature took hundreds to thousands of years to produce
Soil erosion lowers what? soil fertility
Soil erosion can overload what? nearby bodies of water eroded with sediment
What is sheet erosion? surface water or wind peel off thin layers of soil
What is rill erosion? fast flowing little rivulets of surface water make small channels
What is gully erosion? fast-flowing water join together to cut wider and deeper ditches or gullies
Soil is eroding at what rate? faster than it is forming on more than one-third of the world’s cropland
Soil erodes faster than it forms on most U.S. cropland, but since 1985 it has decreased by 40%
What happened in the 1985 Food Security Act (Farm Act)? farmers receive a subsidy for taking highly erodible land out of production and replanting it with soil saving plants for 10-15 years
What is splash (water erosion)? water hits the soil at a severe angle (based on slope) which can erode soil
What is sheet (water erosion)? when surface water moves down a slope or across a field in a wide flow and peels off fairly uniform sheets of soil.
What happens to topsoil during sheet erosion? it disappears evenly, and may not be noticeable until too much damage has been done
What is mass slippage (water erosion)? very wet and large amounts of soil slip away in large chunks called mud slides ex-California
What is Rill (water erosion)? concentrated flow across the surface of soil. its leaves rivets called micro channels
Where does gully erosion happen? on steep slopes where all or most vegetation has been removed.
What is saltation? One particle hitting another and being blown across the surface of the soil
What is suspension? airborne soil. ex- soil from lubbock is found in temple texas
What is surface creep? mountains/sand dunes; surface creeping slowly across. Landslides are an example of a very fast surface creep
How much productivity of the worlds land has been lost due to degraded topsoil? One third
What are the causes of desertification in degrading drylands? Overgrazing, deforestation, erosion, salinization, soil compaction, natural climate change
What are the consequences of desertification in degrading drylands? worsening drought, famine, economic losses, lower living standards, environmental refugees
Repeated irrigation can reduce crop yields by causing what? salt buildup in the soil and water logging of crop plants
What happens during salinization? irrigation water contains small amounts of dissolved salts, evaporation and transpiration leave salts behind, salt builds up in soil
What happens during water logging? Precipitation and irrigation water percolate downward, the water table rises
What are ways to reduce soil salinization? Reduce irrigation and switch to salt tolerant crops such as barley, cotton, and sugarbeet
What are ways to cleanup soil salinization? Flush soil(expensive and wastes water), stop growing crop for 2-5 years, install underground drainage systems (expensive)
White alkaline salts have displaced cops
What are shelter belts and what do they reduce? can reduce wind erosion. Long rows of trees are planted to partially block the wind.
What can shelter belts help to do? retain soil moisture, supply some wood for fuel, and provide habitats for birds
What is minimum tillage? (conservation tillage) to disturb the soil as little as possible while planting crops
What happens during minimum tillage? Special tillers break up and loosen the subsurface soil without turning over the topsoil, previous crop residues, and any cover vegetation
Fertilizers can help do what? restore soil nutrients
What can runoff of inorganic fertilizers cause? water pollution
What are hydrophonic crops? crops grown in fertilized water
What soil is best for plant growth? Loam
When does leaching occur? when humus is dissolved and chemical compounds carried to lower layers
What is not a consequence of desertification? abundant crop harvests
Created by: lasykes