Soil Solutions Continued

aqueous liquid phase of the soil and its solutes

A letter from an expert…

Atomic structure of water

nutrition.jbpub.com/.../chemistryreview6.cfm

Hydrogen Bonding

Water is a powerful solvent

How salt dissolves in water

nutrition.jbpub.com/.../chemistryreview6.cfm

http://www.chem1.com/acad/sci/aboutwater.html

Hydrated ion

http://nmr.ioc.ac.ru/Staff/AnanikovVP/127i-nmr/127i.htm

Inner-sphere complexes

• Interaction between metal ions and ligands where no water molecules are present

• Ions are 'fixed' irreversibly or tightly bound, thus not water-extractable or plant available

Outer-sphere complexes and ion pairs

• Water molecules are positioned between the metal ion and the ligand

• These ions are loosely bound and easily exchanged with other ions in solution

• Ion pairs are uncharged outer-sphere complexes in solution

Schematic diagram illustrating the outer- and inner-sphere Fe-sulfate complexes in water.

http://geoweb.princeton.edu/research/geochemistry/research/aqueous-sulfate-fig1.jpg

http://www.nsls.bnl.gov/newsroom/science/2003/images/01-Peak-figure2.jpg

Fe or Al

O or OH

Surface Complexation of Uranium(VI) Carbonate Adsorbed on Montmorillonite

jeffcatalano.googlepages.com/U_montmor.html

Solvated ion pair

www.theochem.ruhr-uni-bochum.de

Ion pair solvated by water molecules

nmr.ioc.ac.ru/Staff/AnanikovVP/127i-nmr/127i.htm

Speciation - the distribution of ions and complexes in their various forms (species)

http://www-ocean.tamu.edu/Quarterdeck/QD2.2/Sant-Gill/sant-gillfig2.html

Measurement of soil solution

What to measure: • "intensity" or concentration (how much is

there) – total dissolved quantity of an element,

moles/L, mg/L, or some amount per volume

• "capacity factor" - ability of solids to resupply depleted ions through dissolution, weathering, geochemical cycling, etc.

How to measure soil solution

• In situ – Use lysimeters, suction cups, or collect

drainage from soil. – very difficult due to changing water contents

and redox conditions, precipitation of compounds near collection points, access to soil pores, etc

http://www.maf.govt.nz/mafnet/schools/activities/swi/swi-04.htm

Combined tensiometer-

soil solution sampler

hopmans.lawr.ucdavis.edu/images/research_2_5.jpg www.decagon.com

Pore water

sampler

Measuring soil solution in laboratory more common, but not as accurate

• Displacement techniquesWith or w/o non-polar displacing chemicals

• Centrifugation (spinning the soil at a high speed pulls the liquid out of the pores)

• Saturation paste extracts or any ratio of soil to water mixture

Displacement by a non-polar chemical (e.g., CCl4)

http://commons.wikimedia.org/wiki/Image:Carbon-tetrachloride-3D-balls.png

Saturated Paste Extracts

Collecting soil solution

http://www.envisci.ucr.edu/faculty/graham/students/photos/blee05.jpg