Dynamics of soil Organic matterHistorical Development

1. Initial Period: Second half of 18th century and beginning of 19th century

2. First half of 19th century: Study of chemical nature of Humic Substances

3. Second half of 19th century: study of humic substances as natural components – Biological nature of Soil Humic Substances

4.First two decades of 20th century: Contradictions on the nature and development of Soil Humic Substances – Chemical and Biological nature of SOM was recognized

5.Further investigations during the 20th century: Chemistry of Humus, Peat, Coal and other such constituents – synthesis of Humic Substances

6. Present developments in the study of Soil Humus

1. Initial PeriodScientist

Contribution

Wallerius (1761)

Book on Agricultural chemistry – Humus formed by decomposition of plants – Plant food possessing properties of absorption of water and nutrients

Lomonosov (1763)

Book on First Principles of Metallurgy or Mining - humus originated from rotting of animal and plant residues with time

Komov (1782)

Book on Agriculture – role of humus on soil fertility – Apply Organic Manures – Wider Sowing of Perennial Grasses

Achard (1786)

Isolated Humic Substances from Peat by treating with alkali – Acidified – Dark Amorphous PPT

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1. Initial Period ContinuedScientist ContributionVanquelin, 1797

Humic substances from xylem of plants infected with fungi

Thomson, 1807

Proposed the name “Ulmin” for the above substances

DeSaussure, 1804

Humus contains more C and less H and O. Humus Nutrition Theory

Thaer, 1809 Humus Nutrition Theory further developed – Humus sole and direct source of nutrients

Braconnot, 1807, 1819

Brown alkali soluble extracts from carbohydrates and plant residues by treating with mineral acids – named them as Ulmin

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II. First Half of 19th centuryScientist Contribution

Boullay, 1830 Glucose heated with alkali – Dark liquid – Acidified – Brown flocculent precipitate – Ulmic acid

Sprengel, 1826, 1837

Humic acid has 58% C. Properties of HA and its salts – Differential Solubility – Humus Coal – Acid nature of HA – Silicic acid from Silicates – Combines with Bases – Sweet Humus – poor fertility in peats

Berzelius, 1806, 1839 Text Book of Chemistry

Identified black coloured HS soluble in alkali, Yellow coloured crenic and apocrenic Acids, and inert Humin equivalent to Sprengel’s Humus coal – Isolation, Composition and Properties of Salts – Humus Nutrition Theory – Organic Manure Application

Sibirtzev, 1901

Role of crenic and apocrenic acids in soil forming processes – crenic acids – podzol soils

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II. First Half of 19th century Contd.Scientist Contribution

Malaguti, 1835

Artificial Humic Substances – identical with Natural HS – Humification is a dehydration process – C22H12O11=C12H12O6 + 5H2O

Mulder, 1840, 41, 61 and 62

Natural and Artificial HS – Chemical Composition and Properties – identified three types of HS – Insoluble in alkali (Humin and Ulmin), Soluble in alkali (HA, Brown & UA, Black), Soluble in water (Crenic & Apocrenic Acids, Black) – HS chemically individual compounds - N, a contaminant – Purified and dehydrated – chemical composition determined – Ulmin, C40H32O11 – Humin, C40H30O15 – UA, C40H28O12, HA, C40H24O12 or C40H30O15 – CA, C40H24O16,

AA, C24H12O12

II. First Half of 19th century Contd.

Scientist Contribution

German 1836, 37, 41, 42 & 45

HS not chemically individual cpds – Humus Nutrition Theory – Cultivated soils had less humus than virgin soils – Isolated 16 different HS – Mainly three groups of Berzelius and Mulder – HA & UA, Crenic & Apocrenic and humin & Ulmin, based on composition rather than structure – criticized A Manufacturer Of HS – N as constituent of humus – not contaminant

Other HS isolated

Mudeous acid of Johnson, Fumic acid of Thenard,Lignoic acid of Hesse,Hymatomelanic acid of Hoppe - Seyler

1. Studies on Chemical Nature of HS2. Isolation of New HS – Crenic &

Apocrenic Acids3. New Classification Schemes of HS

Misconceptions

Summary of Investigations – Second Phase

1.HS – Chemically individual cpds2.Chemical nature, structure &

properties not known3.Chemical methods to reproduce

humification of plant materials

Second Half of 19th centuryScientist Contribution

Eggerts, 1889 Crenic & Apocrenic acids natural products – criticized HA, UA & Humus Coal

Van Bemmelen, 1888

complexity of chemical composition – HS amorphous and colloidal

Baumann, 1909

HS complex mixture of plant & animal residues in varying stages of decomposition – cannot be separated

Baumann & Gully, 1910

Acid nature of HS not due to functional groups but colloidal properties

Liebig, 1840 Mineral Nutrition theory as against humus theory – Humus only C source

Second Half of 19th centuryScientist Contribution

Grandeau, 1872

Mineral Humus Theories combined – Organo Mineral Plant Nutrition Theory – HS dominant role in dissolving, absorbing and exchange reactions in soils

Pasteur, van Post, Darwin, 1882, Kostychev, 1886, 89, Muller, 1887, Ramann 1888

Humus not chemical or physical but biological with diverse activities of microbes, protozoa, and various other organism

Kostychev, 1890, Schloesing, 1902, Dehrain, 1888, Dehrain and Demoussy, 1896

Humus source of plant nutrients – promotes soil structure – favourable air and water regimes in soil

Second Half of 19th century Contd.Scientist Contribution

Dokuchaev, 1883Kostychev, 1886

“The Russian Chernozems”“Soils of the Chernozem of Russia”Biological Activity – Perennial Grassy Vegetation – Chernozem Formation

Sibirtzev, 1900 - 01

Role of Crenic and Apocrenic acids in podzol formation

Hoppe Seyler, 1889

Biochemistry of decomposition of some organic substances

Omelyansii, 1902

Biochemistry of decomposition of Cellulose

Van Iterson, 1904

Anaerobic Decomposition of Cellulose

Snyder, 1898 and Suzuki, 1906 – 08

Humification of isolated carbohydrates, oils and fats

Second Half of 19th century Contd.Scientist Contribution

Kostychev, 1886Hebert, 1892Dehrain, 1902

HS formed by synthesis between proteins and encrusting substances

Walksman, 1937

Lignoprotein complexes form the nucleus of humus

Summary HS formed by two reciprocal processes – decomposition and synthesis

Participation of two or more plant materials in the process

Biological activity plays a major role in humus synthesis

Resistant compounds like lignins and pectins encrust soluble cpds like proteins