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.