sticking to it gk-12 workshop october 5 th 2011. part i: soil texture what is soil texture how do...
TRANSCRIPT
Sticking To It
GK-12 WorkshopOctober 5th 2011
PART I: Soil Texture
• What is soil texture• How do you measure it?• What is your soil like at your school using a
NRCS map?• What is your soil texture if you use the
sedimentation method?
Soil texture
SAND: 0.05 – 2.00 mmSILT: 0.002 – 0.05 mmCLAY: < 0.002 mm
Source: Brady, N & Weil R
Example:15% sand15% clay70% silt
Texture by feel method
Preparation: Place approximately 2 tsp. soil in palm Add water slowly and Knead soil to break down all chunks Consistency like moist putty
Source: Dr. Del Mokma
Texture by feel method
1. soil will not cohere into a ball, falls apart: sand2. Soil forms a ball, but will not form a ribbon:
loamy sand
Source: Dr. Del Mokma
(c)
Gritty, noncohesive appearance and short ribbon sandy loam
Silt loam (smooth)
Clay (smooth and long ribbon)
Source: Brady, N & Weil R
Web soil surveyhttp://websoilsurvey.nrcs.usda.gov/app/HomePage.htm
Sedimentation method
Layer D: organic materials
Layer C: Clay
Layer B: Silt
Layer A: Sand
Stokes’ law
Velocity V(cm/s)= K D2
K = 11,241 cm-1 sec-1
• Sand: D = 1 mm= 0.1 cmV = 11,241 x (0.1)2= 112.4 cm/sec
• clay: D = 0.002 mm =0.0002 cmV = 11,241 x (0.0002)2= 0.00045 cm/sec
George Gabriel Stokes
Sedimentation method
Layer D: organic materials
Layer C: Clay (2 days-2weeks)
Layer B: Silt (2 hours)
Layer A: Sand (1-2mins)
Each face is 4 mm2
6 faces x 4 mm2 = 24 mm2 Each face is 1 mm2
6 faces x 1mm2 x 8= 48 mm2
2mm 1mm
Diameter (mm) Particles /g Surface Area cm2/g
Sand 2.0 –0.05 90-722 x 103 11 227‐
Silt 0.05 – 0.002 5.8 x 106 454
Clay < 0.002 90 x 109 8 x 106
http://www.theodora.com/wfb/photos/greece/greece_photos_15.html
16g clay
Surface area= 4πa2Volume=
Ball = mm, volume =Marbles= a= mm , volume = mm3 x Number of marbles = mm3
Large ball= a= mm, surface area= mm2Marbles= mm, volume = mm2 x marbles = mm2
Calculating surface area and volume: Measuring in class with balls
Class discussion: Pore sizes
• Different particles sizes have different spaces in between.
• What do you think the pore spaces between clay and sand compare?
• How is this important for air and water?• How would pure clay and sand relate to plant
growth? Why?
Part II: Chemistry
• Using the BeST plots for chemistry– Ions, valence, electronegativity
What is an ion?
• Cation and Anion
• Examples from the BeSt plots
Valence Electrons
• Draw Valance for:• Nitrate, Ammonium, N2, Phosphate, Calcium
ion, etc.
ElectronegativityThe ability of an atom in a molecule to attract shared electrons to itself
http://iws.collin.edu/biopage/faculty/mcculloch/1406/outlines/chapter%202/chap02.html
http://www.mit.edu/~kardar/teaching/projects/dna_packing_website/DNA_chemical_structure.jpg
DNA has a negative charge because of the sugar backbone
http://bioweb.wku.edu/courses/biol115/wyatt/biochem/lipid/P-lipid.gif
http://www.yellowtang.org/images/lipid_bilayer_c_la_784.jpg
http://www.biosci.ohio-state.edu/~prg/protein1.gif
http://biotech.matcmadison.edu/resources/proteins/labManual/images/amino_000.gif
Amino Acids have charge- which determines how proteins fold
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- - - - - - -- - - - - - - - - - - - - -Clay Sand
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• Soil has a net negative charge
• Clay has positive and negative charge and high surface area
http://www.northeastern.edu/chem/faculty_and_research/faculty/geoffrey_davies1/
Lignin
Humic Acids
• Decomposing organic matter has electronegative properties• Gives soil it’s negative charge
Electronegativity in Clay
• -OH group can create electronegativity
• pH can be very important
http://courses.soil.ncsu.edu/ssc051/chapters/images/fig2-2_4.gif
Soi
Mg 2+Al 3+
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- - - - - - -- - - - - - - - - - - - - -Clay Sand
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NH4+
H+
NO3-
Important for Nitrogen Cycle
• Cool facts: DNA and lipids can be found in soil.
• DNA can be bound to clays!• Nitrogen Cycle– Nitrate easily lost– Ammonium can be adsorbed to soil OR nitrified– Nitrogen is usually low (N2)
Conclusion
• Soils in the BeSt plots have different kinds of soil
• The texture could be important for explaining plant growth
• Texture has certain physical and chemical properties which then determines how much water and nutrients are being held.