Ch 3 Soil Organic Matter continued
Pools of Organic Matter (OM) in Soils ACTIVE (labile, ever-changing, mutable) Plant litter Light fraction Microbial biomass Water soluble organics STABLE (Humus) recalcitrant, long term, products of weathering of labile OM Humic acid Fulvic acid Humin
What Does Organic Matter Do? http://www.soils.umn.edu/academics/classes/soil5611/content/OrganicMatter/
: soilslab.cfr.washington.edu/.../DOMSorption.html
http://www.chm.bris.ac.uk/ogu/images/carboncycle.jpg
0.25 to 1 Mg C/ha/y sequestered in soils as carbonate http://www.chem1.com/CQ/Carbonate.png 0.25 to 1 Mg C/ha/y sequestered in soils as carbonate
Losses due to cultivation are 60-80 Mg C/ha/y http://www.climatescience.gov/Library/stratplan2003/final/graphics/images/SciStratFig7-5.jpg
www.farmscape.cse.csiro.au/.../mod1/fig1-05.gif
The Changing Forms of Soil Organic Matter Additions. When roots and leaves die, they become part of the soil organic matter. Transformations. Soil organisms continually change organic compounds from one form to another. They consume plant residue and other organic matter, and then create by-products, wastes, and cell tissue. Microbes feed plants. Some of the wastes released by soil organisms are nutrients that can be used by plants. Organisms release other compounds that affect plant growth. Stabilization of organic matter. Eventually, soil organic compounds become stabilized and resistant to further changes. http://www.extension.umn.edu/distribution/cropsystems/components/7402_02.html
http://www.ar.wroc.pl/~weber/kwasy2.htm
Composition of SOM SOM = humic + nonhumic substances Mostly C, H, O ~ 90% on a dry weight basis Remaining 8-10% is mostly N, S and Cations C/N ratio ~ 10
Proposed structure of humic acid http://www.rsc.org/ej/gt/2000/b001869o/
Computer generated model of humic acid http://www.rsc.org/ej/gt/2000/b001869o/b001869o-f3.gif