Soil Physics

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Undergraduate Soil Science Flashcards on Soil Physics, created by Sadie Blum on 13/11/2022.
Sadie Blum
Flashcards by Sadie Blum, updated more than 1 year ago
Sadie Blum
Created by Sadie Blum about 2 years ago
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Question Answer
Physical Properties of Soil color, texture, structure
Why is soil texture important? Determines aeration, soil pore space, soil drainage. Affects soil workability. Influences nutrient holding capacity
What causes the formation of soil particles? Weathering
Regarding soil size determination, give the size range of the following: sand, clay, silt. Sand~2.00-0.05mm ; Silt~0.05-0.002m ; Clay~ less than 0.002mm
European and American nomenclature differs…How? What is a similarity? European uses logrithmic scale, but both consider clay to be ≤2um
Describe the chart: what is the difference between the fractions of the left to the right side? Classification of particle size fractions. German is on the left side and American nomenclature is on the right.
What are the two ways to determine soil texture? 1. sieves 2. sedimentation
What is a sieve? often used to separate large particles (gravelly soils)
O.M. can be removed by... H2O2
Soluble salts may be removed by ____ (they inhibit dispersion) water
Carbonates may be removed by... HCl
____ _____ is used to break up aggregates (sodium hexametaphosphate) dispersing agents
Who made up Stokes Law? George Gabriel Stokes
In the analysis of sedimentation, Stokes Law is used. What is stokes law?
What is the finger test? Determining soil texture by feel
As particles become smaller, the deviation from perfect sphere becomes more critical. deviation from spherical shape increases ..... surface to volume ratio
Access to surfaces on clay particles may be impeded by: *organic matter *films of weathered minerals *formation of micro-aggregates
What is important to note about packing of particles? particles cannot pack 110% even with extremely fine particle size
What is pore space? volume not occupied by particles
What is a matrix? particles + pore space
What is 1 pointing to? Microphage
What is 2 pointing at? Macrophage
what is a contact point? where particles touch
the more contact points, the ____ the soil strength. higher
What is bulk density? the mass per unit bulk volume of soil that has been dried to a constant weight at 105 °C
a soil with a mass of 50 grams after being oven-dried has a volume of 30 cm3 What is bulk density? 50 g/30 cm3 = 1.67 g/ cm3
What is particle density? the mass per unit volume of soil particles
What are some differences between bulk density and particle density?
What is soil porosity? percentage of soil that is pore space or voids
Average soil has porosity of ~50%
Pores are filled with.... air or water (depending on moisture content)
What is soil permeability? the ease with which air, water, or plant roots penetrate or pass through soil
Clayey soils can have ____ total porosity than sand and still be ____ permeable than sand since the pores are small. greater; less
Ideally, ____ particles should have highest density clay
Most soils tend to increase in surface with time. What does this result? changes in pore space, soil strength, etc.
How does human activity affect the soil? usually compress soils, reducing surface area of particles and reducing pore space
Water typically adheres to clay particles due to high polarity
amount of water adhering will impact _____/____ of soil matrix swelling/ shrinkage
Flocculated vs. dispersed particles dispersed=particles unattached to one another flocculated= particles clumped together
Why is flocculation important? water moves mostly in large pores between aggregates. Also, plant roots grow mainly between aggregates.
Most clay particles have a ____ electrical charge. Like charges repel, so clay particles repel one another. negative
_____ can make clay particles stick together (flocculate). Cations
What is an example of a poor flocculator? sodium
What are examples of good flocculators? Calcium and Magnesium
Explain Flocculating Power of Cations Cations in water attract water molecules because of their charge, and become hydrated. Cations with single charge and large hydrated radii are poorest flocculators.
What does SAR stand for? Sodium Adsorption Ratio
explain electrical conductivity Ions in solution conduct electricity, so total amount of soluble soil ions is estimated by measuring electrical conductivity (EC) of soil water extract.
Soil particles will flocculate if concentrations of (Ca2+ + Mg2+) are ____ relative to concentration of Na+ increased
_____ _______ (dispersion and flocculation) depends on the balance (SAR) between (Ca2+ and Mg2+) and Na+ as well as the amount of soluble salts (EC) in the soil. aggregate stability
Soil particles will disperse if concentrations of (Ca2+ + Mg2+) are _____ relative to concentration of Na+ decreased
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