stable organic matter - humus. humic substancesnon-humic substances fulvic acidhumic acidhumin i.e....
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Stable Organic Matter - Humus
Humic substances Non-humic substances
Fulvic acid Humic acid Humin
i.e. polysaccharides, proteins, lignins, etc. In their natural or transformed states
soluble in acidsoluble in alkali
insoluble in acidsoluble in alkali
insoluble in acidinsoluble in alkali
Humus
Sparks (2002)
Stable Organic Matter - Humus
Fulvic Acid Humic Acid Humin
Light
yellow
Yellow
brown
Dark
brownBlack
Grey
black
decrease in degree of solubility
increase in molecular weight
increase in carbon content45% 62%
decrease in oxygen content48% 30%
decrease in exchange acidity1,400 500meq100 g-1
meq100 g-1
Sparks (2002) Stevenson (2002)
increase in nitrogen content0.8% 5.0%
Stable Organic Matter - Humus
COOH
COOH
Carboxyl
OH
OH
Alcoholic OH
O
O
Carbonyl(ketone)
NNH
NH2
Amine
Acidic groups
Phenolic OHQuinone
Neutral groups Basic groups
Polyfunctionality
Soil Organic Matter - Composition
O
• Probable structures can be estimated using the dimer concept
O
?
Soil Organic Matter - Composition
O
NH2
O
COOH
O
COOH
N OH
O
COOH
NHO OH
O
Soil Organic Matter - Composition
OR
O
O
OO
O
O
OH
OH
O
OH
O
O
O
OH
O
Carboxyl
dimerOH
Alkyl chain
Phenolic - OH
OCarbonyl
NH2
Amine
Soil Organic Matter - Composition
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