SWS3022 Exam 3 Questions and Answers
Chroma - Answer-Strength of the spectral color (peach to neon orange); high concentrations of Fe cause soils to have a high chroma number
Sand particle size separates - Answer-Mostly visible, gritty. Quartz. 0.2-0.05 mm.
Silt particle size separates - An...
How does texture affect overall porosity? - Answer-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.
How does texture affect water and gas movement in soils? - Answer-Coarse-textured
soils have bigger pore spaces and smaller total porosity, allowing water and gas to
move much faster.
Why are the proportions of soil particles important? - Answer-The proportions of sand,
silt, and clay determine which soil textural classes a sample belongs to.
How many textural classes are there? - Answer-12; sand axis on the bottom, clay axis
on the left, silt axis on the right, increasing clockwise
What is the relationship between soil texture and specific surface area? - Answer-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.
What does Stokes' Law define? - Answer-Stokes' Law allows determination of the
time required for different particle size
separates to settle from a suspension; settling velocity of particles in water; V=KD^2
What is Stokes' Law? - Answer-By 2 minutes, sand settles out
By 6 hours silt settles out
Numerical value for soil particle density - Answer-2.65 g/cm3
, The range in bulk densities for a typical soil containing approximately 1-5% organic
matter - Answer-1.0 to 1.6 g/cm3
How does texture, organic matter, aggregation, compaction, and depth in profile affect
porosity and bulk density? - Answer-Factors which increase porosity, decrease density.
And factors which increase density, decrease porosity.
Small pores slow water and gas movement, but increase contact between soil solution
and soil particles, increasing reactivity.
Less OM increases bulk density.
Compaction increases soil density.
Depth in profile = increased compaction, less OM and fewer roots.
What is the difference between total porosity and pore size distribution? - Answer-Total
porosity: the fraction of total soil volume that is pore space. (Vp/Vs)
Pore Size Distribution:
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.
What is soil structure and how can it affect soil porosity and pore size distribution? -
Answer-Arrangement of grouping of individual soil particles into secondary units.
Poor soil structure can inhibit infiltration of water, water movement, and growth of roots.
Very important in clayey soils to prevent water & air restriction.
Granular soil structure - Answer-Characteristic of surface soils, prominent in grasslands.
The product of organic matter and organisms. Very rounded edges.
Class (size): fine
Platy soil structure - Answer-Thin, horizontal plates. Often inherited from parent
material.
Class (size): medium
Often located in subsurface horizons (B-horizons) and promotes drainage in B-horizons
Class (size): coarse
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