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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.