Lecture 6a Soil Weight and Tillage

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Lecture 6aSoil Weight and Tillage
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Soil Weight Bulk Density

• BD Weight / volume or grams/cc
• Soil Weight 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 gt 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
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Acre Furrow Slice
Tilled Soil
D W
AFS D x W 2,000,000 pounds
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What is an Acre?

• 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.

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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 pole is a discontinued linear measurement
  that is better known as the surveyor's rod (16.5
  feet).
• This term, too, is nearly obsolete.
• 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

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Calculation of soil loss or tons of soil loss
per acre

• 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

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BD problem

• 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(Wt vol.) or (1.2x62.4) (X lbs
  43560 ft2/acre x 3/12 ft)
• X (74.9 lbs x 43560 x 3/12) 815,661 lbs or
• 815661bs 2000lbs/ton 407 tons/acre

Volume LWH or Area H 1 acre 43560ft2
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Particle density

• 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 wt vol of solids 358g 135
  2.65 g/cc
• BD soil wt. soil volume 358 300 1.19
  g/cc
• Porosity pore space soil volume 165 300 x
  100 55

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Particle Density Porosity
Soil Water pore Air pore

• 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

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Porosity

• Porosity (P) the volume of the pores divided by
  the bulk soil volume.
• P pore vol soil volume
• Data from previous slide
• Porosity 165 300 x 100 55
• P 1 BD PD x100 or
• P1-(1.19 2.65)x100
• 1- .44.56 x 100 55

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Bearing Capacity-determined by Soil Texture

• 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

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Shrink / Swell Potential-

• soils with more than 30 clay have a high Shrink
  Swell gt clay more S.S. Potential (if clay is
  21)
• 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.

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Settling of foundation due to unstable soil due
to high shrink swell potential
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Bearing capacity of Materials

• 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

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Chemical Soil Stabilization

• 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.

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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.
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SOIL STRENGTH PENETROMETER

• 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.

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Tillage

• 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.

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Tillage - old
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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.

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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
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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 mankinds 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.h
  tm
• http//video.google.com/videoplay?docid6505199120
  210531414qCHISEL20PLOWhlen

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Tillage - Conventional Cons.

• Conventional - Moldboard plowing, disking,
  planting and cultivating.
• http//video.google.com/videoplay?docid7901297547
  942235489qplowingtotal1839start0num10so0
  typesearchplindex6
• http//video.google.com/videoplay?docid3413143716
  172356867qplowingtotal1833start10num10so
  0typesearchplindex4
• Conservation - leaves crop residue on soil
  surface, leaves clods or ridges, increases
  infiltration and reduces runoff.
• http//video.google.com/videoplay?docid6396536009
  66425831
• http//video.google.com/videoplay?docid1368127058
  493687056qDISKTILLAGEtotal6start0num10so
  0typesearchplindex4

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Conservation TillageAdvantages
Disadvantages

• energy saving
• time savings
• erosion control

• cold spring soils
• disease and insect problems
• lower yields
• compaction relief lt
• OM incorporation lt
• weed control harder

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Chisel Plowing
http//video.google.com/videoplay?docid7585540377
78096590qCHISELPLOWtotal4start0num10so0
typesearchplindex2
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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.
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Disk Plowing

• Similar to Chisel plowing, some residues are
  turned under by the disk lifting and inverting
  the soil.

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Ridge Tillage
The annual ridges are formed by using a rolling
disk bedder, and planting is done after only
minor spring seedbed preparation.
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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.

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Strip Tillage No Ridge

• 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/videopla
  y?docid6518049770349075983qSTRIPTILLAGEtotal
  83start0num10so0typesearchplindex0
• http//www1.umn.edu/umnnews/video/carbon.html

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NO - Till Planting

• 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.

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Turf Tillage

• Objectives Improve Aeration Increase
  Infiltration Ease root movement
• Procedures Coring Slicing

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Coring and top-dressing golf greens
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Soil Erosion in a field with 3 slope with
conventional tillage.
The End