History of Soil Organic Matter Studies Continued, Developments during 20th Century, Contributions by Shmuk, Trusov, Berzelius and others on Soil Organic Matter

1. First two decades of 20th Century
Scientist Contribution
Schreiner, 40 different chemically
shorey &
individual compounds of organic
coworkers, nature – sterols, fats, org N – P
1908 – 1930 cpds – HS not specific
substances
Shmuk, 1924 Specific reserve of organic
substances in the soil overlooked
– soils studied have low humus
content – not typical of majority
soils
Oden, 1912, Identified Humus Coal, FA, HA &
14 , 19 Hymatomelanic acid

2. First two decades of 20th Century
Scientist Contribution
Humus Coal Similar to sprengel’s humus coal,
Berzelius and Mulder’s humin &
Ulmin, Insoluble in water, acid
alkali, partially soluble during
fusion with alkali and black
colour
Fulvic acid Similar to Berzelius Crenic and
Apocrenic acids – yellow to
yellow cinnamonic in colour –
soluble in alkali alcohol –
sensitive & resistant to oxidation
(CA & ACA), 55% C content

3. Humic acid
in the
water
extracts
with
Calcium
Carbonate
in the
Lime Stone
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4. First two decades of 20th Century Contd.
Scientist Contribution
Humic Acid Dark Brown to Black colour,
insoluble in alcohol soluble in
alkali, eq. wt 340 58% C
Hymato- Light coloured than HA, Similar
melanic Acid to Ulmic acid, Chocolate Brown,
soluble in alcohol, eq.wt.250 and
62% C
Mis- FA not analogous to CA & ACA
conceptions UA not identical to
of Oden Hymatomelanic acid
HS classification based on
solubility provisional

5. First two decades of 20th Century Contd.
Scientist Contribution
Doyarenko, Protein nature of N fraction of
1901 HA was established
Suzuki, 1906
– 08 Jodidi,
1910 – 13
Kelly, 1914
Sestini, 1902 HA condensation products of N
cpds of polypeptide type –
Aromatic nature established

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7. First two decades of 20th Century Contd
Scientist Contribution
Maillard, 1912 Amino acids and carbodydrates
– 17 reacted – Dark coloured HS of
melanin type obtained –
Condensation reaction –
Microbes help in hydrolysis of
Proteins & Polypeptides
Beijerinck, Enzymatic activity of microbes
1900 Perrier, in biochemical transformation of
1913 HS
Bertrand,
1898

8. First two decades of 20th Century Contd
Scientist Contribution
Trusov, 1914 Classified Plant Materials in to
– 15 two types:
1. Cpds readily utilized by microbes such as
cellulose, hemicelluloses, simple sugars and
organic acids are indirect sources of HS –
first incorporated into microbial plasma and
then utilized in HS synthesis
1. Cpds not readily utilized by microbes like
lignins, tannins and amino acids of aromatic
nature are direct sources of HS

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10. First two decades of 20th Century Contd
Trusov identified three steps in HS formation:
1. Hydrolytic decomposition with formation of
simpler substances of aromatic nature
2. Oxidation of the latter with the formation of
quinones which he called as hydroxy
quinones
3. Further condensation of quinones into dark
coloured complex products
Aromatic compounds by oxidation
and condensation into HS have been
confirmed

11. First two decades of 20th Century
Trusov Contd
– Origin & Biochemistry of humus
formation
Shmuk
– Chemical Nature, Structure and Physico
– chemical properties of HS studied

12. Humic Acid is a High Polymer
Heterogenous Aromatic Compound
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13. First two decades of 20th century Contd
Scientist Contribution
Shmuk
Humic acid most characteristic constituent of
humus with specific nature – not chemically
individual cpds – group of cpds with general
structural features
Oden’s classification of HS based on solubility
only provisional – isolated two fractions – one
soluble and another insoluble from a
chernozem soil

14. First two decades of 20th Century Contd
Shmuk
HS are intermediate between crystalloids and
colloids – but possess properties of colloids
like adsorption, swelling etc.
HA formed esters with alcohol and Benzyl
chloride – Presence of Carboxyl and Hydroxyl
(Phenolic) groups
N, constituent and not contaminant of HA –
secondary origin – source being microbial
plasma

15. The Steelink model of the Humic
Acid Monomer.
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16. First two decades of 20th Century Contd
Shmuk - Established aromatic nature of humic acid –
Found two components in HA (Hoppe Seyler(1889) in
peats)
1. An aromatic N containing compound of microbial
origin
2. Benzene Ring
Two components in chemical linkage and not a mixture –
Shmuk’s ideas together with that of Trusov (Oxdn of
aromatic cpds into quinones and subsequent
condensation) led to present day theory of humus –
condensation of an aromatic cpd with N cpd of protein
origin

17. First two decades of 20th Century Contd
Defects of Shmuk’s works
1. Lignin was the main source of aromatic nature –
But Tannins, Polyphenols also contain aromatic ring
2. Views on humin (alkali insoluble) and crenic &
apocrenic acids as unstable mixture of plant
residues in varying stages of decomposition
differed from contemporary views

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19. First two decades of 20th Century Contd
Williams (1897, 1914)
Humus formation – biologically interrelated
phenomena – equilibrium between reciprocal
processes – life & death; symbiosis &
antibiosis; synthesis of organic cpds in
plants, their decomposition by microbes &
resynthesis into HS
Humus synthesis not a chemical process – Any
organic substance yields black liquids on acid
addition – straw, saw dust etc
Vegetative cover, natural conditions important
for humus formation

20. First two decades of 20th century Contd
Williams (1897, 1914) - Three types of biological
associations;
1. Woody Vegetation and Microbes – Fungi,
Actinomycete and anaerobic bacteria – podzol
formation by crenic acids – woody vegetation
decomposed by anaerobic fungi
2. Meadow Grass Vegetation and bacteria, mainly
anaerobic – Ulmic acid formed – anaerobic
decomposition of grasses – stable crumb structure
3. Steppe Vegetation and aerobic bacteria – humic
acids formed – deterioration of soil structure

21. First two decades of 20th century Contd
General Findings of 20th century
1. Existence of HS as natural products was
convincingly demonstrated
2. Various plant materials during complex
biochemical transformations served as source for
HS
3. Kostychev’s ideas that products of bacterial
synthesis were involved in the formation of HS was
confirmed

22. First two decades of 20th century Contd
General Findings of 20th century
4. HS were considered to be a product of a two stage
process – Decomposition of original plant residues
into simpler compounds and subsequent synthesis
of complex HS
5. HA – condensation products of aromatic nature
with N containing organic cpds
6. Enzymatic activity of microbes was involved not
only during decomposition of plant residues but also
during synthesis of HS

23. Further Investigations during 20th century
Chemistry of humus from coal, brown coal and peat studied by
German Scientists – Fischer & Schrader, 1921-21, Fuchs,
1931-36 – Not strictly applicable to soil HS
Marcusson, 1922 – 27: Cellulose converted to oxycelluloses and
uronic complexes, acquire aromatic nature and get
converted into HS
Fischer and Schrader & Fuchs, 1920 – 30: Lignin undergoes
number of complex transformations, mainly physico
chemical – oxidation, condensation etc. gets converted into
HS

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26. Further Investigations during 20th century
Arguments in favour of Lignin Theory:
1. Similarity in the structure of lignin and HA – Presence of
aromatic ring and functional groups such as Methoxyl
(OCH3) and Phenolic Hydroxyl (OH) group
2. Fischer and Schrader (1922) obtained HS by reacting lignin
with alkali in autoclave. Under similar conditions Cellulose
yielded only weak coloured low molecular weight
compounds (Willstatter & Zeichmeister, 1913)
3. Lignin was relatively resistant to microbial action while
cellulose was rapidly decomposed to low molecular weight
cpds

27. Further Investigations during 20th century
Weak points of Lignin Theory:
1. Similarity in the structure of lignin and HA – Presence
of aromatic ring – Also present in substances of non
lignin origin such as tannins & Polyphenols in plants
2. Fischer and Schrader (1922) obtained HS by reacting
lignin with alkali in autoclave – Unconvincing since
experimental conditions are quite different from
natural conditions
3. Nature of cpds participating in the synthesis of HS and
exact mechanism of humus formation remain obscur

28. Further Investigations during 20th century
Lignin Theory Modified: Hobson & Page, 1932; Waksman &
Coworkers, 1927 – 33)
1. Cellulose and Simple CHOs are rapidly decomposed
2. Hemicellulose and Proteins decomposed and
incorporated into microbial plasma
3. Lignin resistant to decomposition
Two cpds important in Humus Formation
1. Lignin of Plant Tissues
2. Protein resynthesized into microbial plasma
The interaction between the two result in formation
of Ligno Protein Complexes