Term
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Definition
diameter = ~8,000 mi
circumference = ~25,000 mi |
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Term
| The definitions of soil depend strongly on the concerns of those making the definitions. |
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Definition
| The definition of soil is dynamic because many specializations and disciplines view soil differently: ecological, geological, environmental, etc. |
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Term
| Basic functions of soils in the environment? |
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Definition
Medium for plant growth: support, gas and water exchange, temperature control, nutrient storage and release.
Regulator for water supplies: infiltration, runoff, storage, movement, purification |
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Term
| 4 basic processes involved in soil formation? |
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Definition
Transformation
Additions
Losses
Translocations |
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Term
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Definition
(physical and chemical) modifications of elements in the soil.
physical weathering: size & shape, freeze & thaw, plants, weather(reduces size & increases surface area, accelerating chemical weathering)
chemical weathering: synthesis & reorganization of constituents. hydration, hydrolysis, oxidation & reduction, acids, dissolution. |
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Term
| Consolidated - Unconsolidated - Secondary compounds |
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Definition
rocks composed of primary minerals (dominated by Al, Fe, Si, and O).
Chemical weathering transforms primary minerals into secondary minerals which are reactive (aluminosilicate clays, iron oxides, and aluminum oxides) |
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Term
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Definition
| organic material, dust particles, manure, fertilizer |
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Term
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Definition
| erosion of soil materials, decomposition of organic material, movement of salts, clays, and OM |
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Term
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Definition
vertical movement of minerals.
water is the primary agent.
elluviation: light soil colors indicate a loss of materials causing an inert characteristic. creates a zone of reactivity below (illuviation) |
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Term
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Definition
| = a type of transformation that can be physical or chemical |
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Term
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Definition
Climate: high temps and rainfall accelerate soil formation.
Relief:
Organisms: increase OM, profile mixing, nutrient recycling.
Precipitation: increases rates of translocations and eventually transformations.
Time: entisol to ultisol. |
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Term
| What is the parent material that dominates Florida soils? |
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Definition
sandy and clayey marine and alluvial(deposited by rivers and streams) deposited over limestone bedrock.
Mostly calcium and magnesium carbonates from original ocean species like corals and mollusks. |
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Term
| What is the origin of the sediments that ultimately formed the parent materials for Florida soils? |
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Definition
| An influx of continental sediments began about 25 Mya. The sediments were shed from the Appalachian mountains by the lowering sea levels. |
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Term
| How do rainfall and temperature impact soil formation? |
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Definition
| Increased temperature and rainfall both accelerate soil formation. High temperatures increase the rate of physiological processes while water increases the rate of weathering and translocation, ultimately increasing the rate of transformation. |
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Term
| Why are soils in Florida more developed compared to soils in the west? |
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Definition
| In the east there is more rainfall, causing faster weathering and soil transformation. This causes more differentiated soil horizons. |
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Term
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Definition
| the process of soil formation as a result of the combination of soil forming factors and processes |
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Term
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Definition
| roughly parallel layers of soil with varying compositions and properties |
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Term
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Definition
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Term
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Definition
surface organic horizon (>20% OM)
derived from the decomposition of plant and animal residues.
differentiated based on degree on decomposition. |
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Term
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Definition
topmost mineral surface horizon (topsoil).
subject to significant weathering, accumulates OM, often darker than the soil below, high in plant roots and biotic activity, zone of gas and water exchange. |
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Term
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Definition
zone of Elluviation.
maximum losses by translocations (of OM, clays, carbonates, Fe and Al oxides).
generally lighter in color and contains resistant primary materials (like quartz). |
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Term
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Definition
usually a zone of illuviation.
accumulates material (OM, clays, Fe/Al, salts) lost from above or forms in place.
potential color development and high reactivity due to secondary minerals and OM.
subordinate letter indicates what is accumulating. |
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Term
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Definition
| closely resembles parent material, unconsolidated, little or no evidence of alteration or development. |
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Term
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Definition
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Term
| Subordinate soil horizons |
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Definition
a, e, i: apply to O horizon. differentiated based on OM composition. high, moderate, weak.
p: applies to A horizon. disturbed or plowed.
t: applies to B. silica clay. if illuvial, argillic.
h: illuvial OM in B.
w: weak development of color or structure.
g: low oxygen, wet, depletion of Fe. |
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Term
| Relationship between time and degree of soil development. |
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Definition
| Younger soils (entisols) are less developmed and older soils (ultisols) are highly developed and differentiated. |
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Term
| Vertical horizon subdivisions |
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Definition
characterized by similar master and/or subordinate properties separated by degree.
Gradient of increasing clay content with downward movement in B horizon: Bt1, Bt2, Bt3... |
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Term
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Definition
| transitional layers between master horizons, defined by a dominant character (AE, EB, BE, etc..) |
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Term
| Generalizations in respect to soil color |
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Definition
gray/black = OM
orange/red = iron oxides
light colors = removal of materials |
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Term
| 3 components of soil color |
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Definition
Hue: dominant spectral color related to the wavelength of light in proportions of red to yellow.
Value: related to the total amount of light reflected. Lighter colors have higher numbers.
Chroma: strength of the spectral color. High concentrations of Fe cause soils to have a high chroma number. |
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Term
| 3 particle size separates |
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Definition
Sand: mostly visible, gritty. Quartz. 0.2-0.05 mm.
Silt: microscopic, smooth/silky.Quartz. 0.05-0.002 mm.
Clay: sub-microscopic, collodial. Secondary minerals. <0.002 mm. |
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Term
| How does texture affect overall porosity? |
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Definition
| Finer-textured soils have greater overall porosity than coarse-textured soils. Finer soils have smaller pore spaces which increase their capillarity, and allow them to hold water and gases better. |
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Term
| How does texture affect water and gas movement in soils? |
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Definition
| Coarse-textured soils have smaller pore spaces, allowing water and gas to move much faster. |
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Term
| Why are the proportions of soil particles important? |
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Definition
| The proportions of sand, silt, and clay determine which soil textural classes a sample belongs to. There are 12 different soil textural classes. |
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Term
| What is the relationship between soil texture and specific surface area? |
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Definition
| Soils with finer textures have more overall surface area compared to coarse-textured soils. This is important because the more surface area a soil has, the greater its ability for it to hold water, gases, and nutrients. |
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Term
| What is the range in bulk densities for a typical mineral soil containing approximately 1-5% OM? |
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Definition
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Term
| How does texture, organic matter, aggregation, compaction, and depth in profile affect porosity and bulk density? |
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Definition
Factors which increase porosity, decrease density. And factors which increase density, decrease porosity.
Increasing texture/OM increases bulk density.
Compaction increases soil density.
Depth in profile = increased compaction, OM and fewer roots. |
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Term
| Understand the difference between total porosity and pore size distribution. |
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Definition
Total porosity = the fraction of total soil volume that is pore space.
Macropores: >0.08 mm, large freely draining. inter-aggregate pores, large enough to accommodate roots.
Mesopores: 0.08 - 0.03 mm, retains water well against draining. accommdates fungi and root hairs.
Micropores: <0.03 mm, small storage of water. clay, intra-aggregate pores. accommdate bacteria. |
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Term
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Definition
arrangement of grouping of individual soil particles into secondary units.
Poor soil structure can inhibit infiltration of water, water movement, and growth of roots. V important in clayey soils to prevent water & air restriction. |
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Term
| What are the soil structure types? |
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Definition
Granular
Platy
Blocky
Prismatic |
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Term
| Describe the granular soil structure? |
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Definition
characteristic of surface soils, prominent in grasslands. the product of organic matter and organisms. very rounded edges.
class: fine |
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Term
| Describe the platy soil structure? |
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Definition
thin, horizontal plates. often inherited by the parent material.
class: medium |
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Term
| Describe the blocky soil structure? |
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Definition
angular or sub-angular. usually in subsurface horizons (B) and promotes drainage.
class: coarse |
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Term
| Describe the prismatic and columnar soil structures? |
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Definition
vertical orientation, swelling clays.
common in semi-arid regions.
class: very coarse. |
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Term
| 2 forces responsible for water movement in soils |
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Definition
gravity: the downward pull of gravity on water.
capillarity: spontaneous movement of water into and through pore spaces in the soil without the aid of gravity. |
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Term
| How do adhesion and cohesion work together to create capillarity in soils? |
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Definition
adhesion is the attraction of water molecules to a surface and cohesion is the attraction of water molecules to one another (hydrogen bonding).
adhesion allows attraction to pore walls and cohesion allows water to suspend itself within pore walls. |
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Term
| How does pore radius impact the strength of capillary forces? |
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Definition
Capillarity is inversely proportional to the pore radius. Capillarity is measured by the height of the pore.
h = 0.15 / r |
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Term
| What is potential energy and what are the three types in soil? |
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Definition
potential energy: energy waiting to be used or exploited.
gravitational
capillary (matric)
pressure |
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Term
| Why is gravitational potential energy not impacted by soil properties? |
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Definition
| Gravitational potential energy is only due to the height of any object above a reference point. The higher the elevation, the greater the gravitational potential energy. |
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Term
| In an unsaturated soil, what is the sign of the capillary potential? |
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Definition
| It is negative because negative pressure (suction) is required to pull water into the pore spaces. |
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Term
| What conditions create potential pressure energy? |
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Definition
| When a soil is saturated, all pore spaces are filled, and the water will exert a downward pressure that forces water through lower pore spaces. This results in a downward flow. The pressure potential is positive. |
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Term
| What is plant available water? |
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Definition
The difference between field capacity and permanent wilting point.
Field capacity: water in soil after drainage by gravity
Permanent wilting point: level of water content where plants can no longer access water (suction = ~15,000 cm) |
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Term
| How do you determine if water will flow between two points? |
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Definition
The gradient is the driving force for water to flow.
The larger the gradient, the more likely water will flow. |
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Term
| What is hydraulic conductivity? How is it affected by soil properties? |
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Definition
(K) is the ease with which water moves through soils.
Texture, density, structure, and water content all impact hydraulic conductivity. In fine-textured soils there is high porosity, and therefore there will be poor hydraulic conductivity; water will flow poorly.
In soils with high densities there is a strong porosity, causing low hydraulic conductivity. |
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Term
| How does water content of a soil affect hydraulic conductivity? |
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Definition
Under saturated conditions there is maximum conductivity because there are no available pores to suction water.
With a low water content there are available pores and they will suck water in, causing low hydraulic conductivity. |
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Term
| How is the overall flow of water determined? |
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Definition
| Darcy's equation. hydraulic conductivity (K) * gradient |
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