Lecture 6a
Soil Weight and Tillage
Soil Weight & Bulk Density
Note: Since gravity will not change we will use mass and weight interchangeable.
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BD = mass / volume or
grams/cc
Soil mass = BD x Volume
BD always measured on oven
dry soil (water is not
considered in BD
calculations)
BD changes as the pore
space changes ie. compaction
= > BD
BD of common surface soils =
1.1 - 1.4 g/cc
BD of common subsoils = 1.3 1.7 g/cc
Using a penetrometer to measure
soil bulk density indirectly
Acre Furrow Slice
Tilled Soil
D
W
AFS = D x W = 2,000,000 pounds
What is an Acre?
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An acre was initially defined as the
area that a man and ox could
cultivate in one day. In France the
equivalent area was called a journal
(in French jour means day). (about
size of a football field)
Medieval period acres varied from
locale to locale as can be imagined.
Eventually uniformity came about, at
least in Britain. There a 10-acre
square was defined as a furlong on
each side.
Football field is about 1.3 acres
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Furlong is Old English and originated as
furh (furrow) + long, i.e. a long furrow.
A furlong measures 1/8 mile, 220
yards, 660 feet, or 60 poles.
The furlong, the "long furrow", came
into use only after the adoption of the
horse (and horse collar) and the heavy
wheeled plow. Until then, with oxen and
a light plow, which could be easily
turned, the fields were more or less
square. DG Baker
Calculation of soil loss or tons of soil loss
per acre
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1 g water = 1cc
& 1 ft3 water = 62.4 lbs
example soil BD = 1.2g/cc or
the soil is 1.2 times heavier than water or
ratio of soil and water = 1/1.2 = 62.4/X
or X = 1.2 x 62.4 = 74.9 lbs. per cubic foot
BD problem
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For soil with BD of 1.2g/cc
that lost 3 inches of
soil per acre how many
tons of soil were lost?
Solution:
BD=
(mass(x) ÷ vol.) or
(1.2x62.4) = (X lbs) ÷ (43560 ft2/acre x3/12 ft)
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X = (74.9 lbs/ft3 x 43560 ft2 x 3/12 ft.) =
815,661 lbs or
815661bs ÷ 2000lbs/ton = 407 tons/acre
Volume = L×W×H or Area × H & 1 acre = 43,560ft2
Particle density
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Particle density is the mass of the soil particles divided by the
volume of the soil particles
Particle density normally is 2.65 g/cm3
Example:
Soil Core = 300 cc = volume of soil (soil particles + pore space)
pore space = 165 cc, (only volume of soil pores)
solids = 135cc , (volume of soil particles)
Soil weight = 358g
PD = soil mass ÷ vol. of solids = 358g ÷ 135 = 2.65 g/cc
BD = soil mass ÷ soil volume = 358 ÷ 300 = 1.19 g/cc
Porosity =pore space ÷ soil volume = 165 ÷ 300 x 100 = 55%
Particle Density & Porosity
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Between soil particles
and organic matter
are open spaces called
pores
Water which fills all
or parts of the pores
is soil water
Soil porosity directly
influences soil water
movement
Soil
Water pore
Air pore
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=
Porosity (P)
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Porosity (P) = the volume of
the pores divided by the
bulk soil volume.
P = pore vol ÷ soil volume
Data from previous slide:
Porosity = 165cc ÷ 300cc x 100 = 55%
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P = {1 –{ BD ÷ PD} }x100 or
P={1-(1.19 ÷ 2.65)}x100
= 1- .45 =.55 x 100 = 55% porosity
Bearing Capacity-determined by Soil Texture
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Ability of the soil to withstand a
load
Or the average load per unit area
that will cause failure by rupture of
a supporting soil mass.
Soil stabilization - any method that
prevents a soil system from moving
under a load.
Compaction - increase the density thereby increasing stability - apply
large pressure to soil at optimum
moisture
Shrink / Swell Potential
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soils with more than 30%
clay have a high Shrink
Swell > clay more S.S.
Potential (if clay is 2:1)
to avoid this problem soil
must be compacted and
water must be kept out.
without the above Shrink/swell will crack
foundations and pavements
or move telephone poles.
Settling of foundation due to unstable soil due to high
shrink swell potential
Bearing capacity of Materials
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Load bearing Pressure (psf)
Crystalline Bedrock
12,000
Sedimentary rock
6,000
Sandy gravel or gravel
5,000
Sand, silty sand, clayey sand, silty gravel and clayey
gravel
3,000
Clay, sandy clay, silty clay, and clayey silt
2,000
Psf ( pounds per square foot)
BOCA National Building Code, 1996
Chemical Soil Stabilization
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Lime, cement, and
pozzolan (high silica
volcanic ash) can be
used as chemical
additives.
Lime is most effective
on clay soils, and can
be used in combination
with cement and
pozzolan.
Loss of bearing capacity - a wet soil allowed this heavy tractor to
sink in to the axels. It required a pull to become un-stuck.
SOIL STRENGTH PENETROMETER
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This penetrometer is a
easy and reliable method
for determining in-place
soil strength.
Great for checking building
pads, excavations, or
potential building sites.
Simply measure the
penetration and look up soil
strength on the strength
chart included with the
unit.
Tillage
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Soil tillage - oldest procedure of agriculture to manipulate
the soil to improve crop production.
Farmers of Burkino Fasso (West Africa) preparing their land for planting.
Tillage - old
Tillage - Modern
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Tillage uses more
energy than any
other cropping
procedure.
Tillage requires time,
since lifting the soil
and moving it can not
be done rapidly.
Tillage - Objectives
Preparation of seedbed
 Control of weeds
 Fluff soil - reduce bulk density
of root zone
 Soil and Water conservation
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Compaction
The Plow
A plow is a wedge that is dragged through
the soil by a draft animal or a tractor.
It cuts away the top layer of soil.
The plow lifts and turns over the soil layer.
The plow is one of mankind’s oldest
machines.
Wooden plows have been in use for about
5000 years. Metal plows date back less than
200 years.
http://www.historyforkids.org/learn/economy/plow.htm
http://video.google.com/videoplay?docid=6505199120210531414&q=CHISEL%20PLOW&hl=en
Tillage - Conventional & Cons.
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Conventional Moldboard plowing,
disking, planting and
cultivating.
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http://video.google.com/videoplay?docid=79012975479422354
89&q=plowing&total=1839&start=0&num=10&so=0&type=sear
ch&plindex=6
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http://video.google.com/videoplay?docid=3413143716172356867&q=
plowing&total=1833&start=10&num=10&so=0&type=search&plindex
=4
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Conservation - leaves
crop residue on soil
surface, leaves clods
or ridges, increases
infiltration and
reduces runoff.
http://video.google.com/videoplay?docid=639653600966425831
http://video.google.com/videoplay?docid=1368127058493687056&q=
DISK+TILLAGE&total=6&start=0&num=10&so=0&type=search&plind
ex=4
Conservation Tillage
Advantages
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energy saving
time savings
erosion control
Disadvantages
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cold spring soils
disease and insect
problems
lower yields
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compaction relief <
OM incorporation <
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weed control harder
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Chisel Plowing
http://video.google.com/videoplay?docid=758554037778096590&q=CHISEL+PLOW&total=4&start=0&num=10&so=0&type=search&plindex=2
Chisel Plowing
This system does not turn the soil over, but rather
leaves it rough with clods of soil, with plenty of crop
residue remaining.
The soil density and amount of covering depends
on the depth, size, shape, spacing, of the chisel
blades.
The residue and rough, cloddy surface of the soil
reduces raindrops impact and reduces runoff
velocities, thus reducing erosion.
Disk Plowing
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Similar to Chisel plowing, some residues
are turned under by the disk lifting and
inverting the soil.
Ridge Tillage
The annual ridges are formed by using a
rolling disk bedder, and planting is done
after only minor spring seedbed preparation.
Ridge tillage
The extent of soil conservation depends on the
amount of residue left and the row
direction. Planting on the contour plus
increased surface residues greatly reduce
soil loss.
Strip Tillage –No Ridge
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Strip tillage aims to retain
crop residues, and establish
crops with the least amount
of soil disturbance while still
maintaining crop yield.
Strip till techniques often
involve fully cultivating a strip
that is about one third of the
row spacing wide.
The rest of the soil is left
undisturbed, and provides a
good carriage way for
vehicles passing through the
crop.
http://video.google.com/videoplay?docid=65180497703490759
83&q=STRIP+TILLAGE&total=83&start=0&num=10&so=0&typ
e=search&plindex=0
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http://www1.umn.edu/umnnews/vid
eo/carbon.html
NO - Till Planting
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All planting requires:
placing seed at accurate depth
 pressing and covering seed so
each has an equal chance for
germination & emergence,
This provides uniformity and
predictability of crop
establishment.
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No till
This planting system prepares
a seedbed 2 inches wide or
less, leaving most of the
surface undisturbed and
still covered with crop
residues.
The result is a wetter, colder
environment that protects
the seed and soil with its
insulating effect of the
surface residue.
Turf Tillage
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Objectives
Improve Aeration
Increase Infiltration
Ease root movement
Procedures
Coring
Slicing
Coring and top-dressing golf greens
Dyad
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Describe conservation tillage that you have seen or done, or describe some turf tillage that you have observed or participated in.
Soil Erosion in a field - 3% slope
& conventional tillage.