Sticking To It
GK-12 Workshop
October 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 mm
SILT: 0.002 – 0.05 mm
CLAY: < 0.002 mm
Source: Brady, N & Weil R
Example:
15% sand
15% clay
70% 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: sand
2. Soil forms a ball, but will not form a ribbon:
loamy sand
Source: Dr. Del Mokma
Gritty, noncohesive appearance and short ribbon
sandy loam
Silt loam (smooth)
Clay (smooth and long ribbon)
(c)
Source: Brady, N & Weil R
Web soil survey
http://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 cm
V = 11,241 x (0.1)2= 112.4 cm/sec
George Gabriel Stokes
• clay: D = 0.002 mm =0.0002 cm
V = 11,241 x (0.0002)2= 0.00045 cm/sec
Sedimentation method
Layer D: organic materials
Layer C: Clay (2 days-2weeks)
Layer B: Silt (2 hours)
Layer A: Sand (1-2mins)
2mm
Each face is 4 mm2
6 faces x 4 mm2 = 24 mm2
1mm
Each face is 1 mm2
6 faces x 1mm2 x 8= 48 mm2
Surface Area cm2/g
Diameter (mm)
Particles /g
Sand 2.0 –0.05
90-722 x 103
Silt 0.05 – 0.002
5.8 x 106
454
Clay < 0.002
90 x 109
8 x 106
11 ‐ 227
16g clay
http://www.theodora.com/wfb/photos/greece/greece_photos_15.html
Calculating surface area and volume:
Measuring in class with balls
Volume=
Surface area= 4πa2
Ball = mm, volume =
Marbles= a= mm , volume = mm3 x Number of marbles = mm3
Large ball= a= mm, surface area= mm2
Marbles= mm, volume = mm2 x marbles = mm2
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.
Electronegativity
The ability of an atom in a molecule to attract shared electrons to itself
http://iws.collin.edu/biopage/faculty/mcculloc
h/1406/outlines/chapter%202/chap02.html
DNA has a negative charge
because of the
sugar backbone
http://www.mit.edu/~kardar/teaching/project
s/dna_packing_website/DNA_chemical_struct
ure.jpg
http://bioweb.wku.edu/courses/
biol115/wyatt/biochem/lipid/Plipid.gif
http://www.yellowtang.org/images/lipid_bilay
er_c_la_784.jpg
Amino Acids have charge- which determines how proteins fold
http://www.biosci.ohiostate.edu/~prg/protein1.gif
http://biotech.matcmadiso
n.edu/resources/proteins/l
abManual/images/amino_0
00.gif
Clay
- - - - -- -- -- - - -- -- - - - - ------- ------------- - - - -- -- -- - ------ - - - ------------------------------------• Soil has a net negative charge
• Clay has positive and negative
charge and high surface area
Sand
- - - -- - -
• Decomposing organic matter has electronegative properties
• Gives soil it’s negative charge
Humic Acids
Lignin
http://www.northeastern.edu/chem/faculty_and_rese
arch/faculty/geoffrey_davies1/
Electronegativity in Clay
• -OH group can create electronegativity
• pH can be very important
Soi
Mg 2+
http://courses.soil.ncsu.edu/ssc051/chapters/i
mages/fig2-2_4.gif
Al 3+
Clay
Sand
- - - - -- -- -- - - -- -- - - - - ------- ------------- - - - -- -- -- - ------ - - - - - ------------------------------- - - -- -- -- -- - - NO3- - NH4+
H+
-- - -- -
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.