physical properties Flashcards
function of soil in an ecosystem
physical environment for plat to root in (seed/soil contact important), provides water, aeration, nutrient source and heat.
soil as a rooting medium
root space important - root is strong but it can’t make its own pores, porosity, pore continuity, soil material strength
importance of pore size
more like im-pore-tant, pore size is key.
water sticks to pore surfaces, surface tension. allows for root travel, water holding, and airation
physical properties of soil
texture, structure, shrink/swell potential, compressibility, frost susceptibility.
all of this is summed up into:
- particle density
- bulk density
- porosity
soil texture meaning in a nutshell
relative proportion of mineral particles of a different size.
sand is coarse, silt is flower-like, and clay is sticky/paperlike
sand particle size
2.0-0.05mm
silt particle size
0.05-0.002mm
clay particle size
<0.002mm
development of soil texture
water/glaciation or wind, not management.
significance of soil texture
volume and pore size - water movement, aeration, roots, and surface area
how to determine soil texture
many methods, hydrometer (lab), pipette, or using stokes law
stokes law
disperse soil in a salt water, measure time to sink a certain distance.
measure using the smallest diameter - bigger diameter would’ve already fallen by then.
V=Kr^2, t=h/Kr^2
K=34700cm/s
pipette method
measure controlled amount of water, boil it down to determine weight difference and whatever at diff times
hydrometer
idk, something w density
particle size distribution curve
measure how much in suspension at a size, every soil type can still have diff curves.
soil structure
arranging primary soil particles and organic matter to definable secondary structures like aggregates
for plants, need root/air/water space
granular soil structure
enough small pores for seed-soil contact, and pores for roots and shoots
how are soil structures formed?
drying/wetting, freezing/thawing, biological activity
crop impact of freezing and thawing
perennial crops with tap root (really deep one) get impacted - freezing in the root splits it and pushes it up, causing winter kill. more snow insulates the ground better and reduces winter kill
organic content on soil stability
good, great even, maybe. perhaps. very good for soil stability no cap
characterization of soil structure
particle density, bulk density, volume fraction of pores (pore space ratio). basically pore size distribution and continuity
bulk density
dry soil mass/volume of soil.
sand has most density, clay has least
think of it like water holding ability.
tillage can reduce BD, if only for a moment.
particle density
soil solid mass (dried)/volume of solids
kinda a constant
pore space ratio
1-bulk density/particle density
clay has the largest ratio, sand has smallest
pore size
big - macro, small - micro, middle - meso
varies w texture and structure, clay soils have ,ore mircopores than sands, sands have more macro than clays
clay has smaller particles itself
mirco pore significance
have strong capillary action, holds water on the surface, water is not plant available bc can’t be sucked out
meso pore significance
plant available water, variable porosity, where lil hairy roots can go
Marco pore significance
not a lot of capillary action, drains out easily, keeps soil oxygenated, allows air flow. roots grow in large pores, can’t create new pores
compaction
increase in bulk density - loss of large pores. large pores go first and easiest, break into small ones. more water, less air/roots.
sand not easily compacted, clay easily compacted. bc of pore space ratio
tractor compaction
most at contact point, not as much impact further down. wider wheels decrease compaction
shear
soil pushed around a load - not as much compaction as it looks
higher BD on root structure
shorter, thicker roots, not as much water access
lower BD on root structure
more drought hardy, long thing roots increase surface area and water intake
erosion
small aggregates picked up and brought away. reduced by slowing water down, reducing a slope and slowing potential
management practices to improve soil structure -
no
