Som lecture 1


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History of Soil Organic Matter Studies, Developments during early 18th and 19th centuries, Contribution by Various Scientists on SOM studies

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Som lecture 1

  1. 1. Dynamics of soil Organic matter Historical Development1. Initial Period: Second half of 18th centuryand beginning of 19th century2. First half of 19th century: Study of chemicalnature of Humic Substances3. Second half of 19th century: study of humicsubstances as natural components –Biological nature of Soil Humic Substances
  2. 2. 4.First two decades of 20th century: Contradictions on the nature and development of Soil Humic Substances – Chemical and Biological nature of SOM was recognized5.Further investigations during the 20th century: Chemistry of Humus, Peat, Coal and other such constituents – synthesis of Humic Substances6. Present developments in the study of Soil Humus
  3. 3. 1. Initial PeriodScientist ContributionWallerius Book on Agricultural chemistry – Humus formed(1761) by decomposition of plants – Plant food possessing properties of absorption of water and nutrientsLomonosov Book on First Principles of Metallurgy or Mining -(1763) humus originated from rotting of animal and plant residues with timeKomov Book on Agriculture – role of humus on soil(1782) fertility – Apply Organic Manures – Wider Sowing of Perennial GrassesAchard Isolated Humic Substances from Peat by treating(1786) with alkali – Acidified – Dark Amorphous PPT
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  5. 5. 1. Initial Period ContinuedScientist ContributionVanquelin, 1797 Humic substances from xylem of plants infected with fungiThomson, 1807 Proposed the name “Ulmin” for the above substancesDeSaussure, Humus contains more C and less H and O.1804 Humus Nutrition TheoryThaer, 1809 Humus Nutrition Theory further developed – Humus sole and direct source of nutrientsBraconnot, Brown alkali soluble extracts from carbohydrates1807, 1819 and plant residues by treating with mineral acids – named them as Ulmin
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  7. 7. II. First Half of 19th centuryScientist ContributionBoullay, 1830 Glucose heated with alkali – Dark liquid – Acidified – Brown flocculent precipitate – Ulmic acidSprengel, 1826, Humic acid has 58% C. Properties of HA and its1837 salts – Differential Solubility – Humus Coal – Acid nature of HA – Silicic acid from Silicates – Combines with Bases – Sweet Humus – poor fertility in peatsBerzelius, 1806, Identified black coloured HS soluble in alkali,1839 Text Book Yellow coloured crenic and apocrenic Acids, andof Chemistry inert Humin equivalent to Sprengel’s Humus coal – Isolation, Composition and Properties of Salts – Humus Nutrition Theory – Organic Manure ApplicationSibirtzev, 1901 Role of crenic and apocrenic acids in soil forming processes – crenic acids – podzol soils
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  9. 9. II. First Half of 19th century Contd.Scientist ContributionMalaguti, Artificial Humic Substances – identical with1835 Natural HS – Humification is a dehydration process – C22H12O11=C12H12O6 + 5H2OMulder, 1840, Natural and Artificial HS – Chemical41, 61 and 62 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
  10. 10. II. FirstScientist Half of 19Contribution th century Contd.German HS not chemically individual cpds –1836, 37, 41, Humus Nutrition Theory – Cultivated42 & 45 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 contaminantOther HS Mudeous acid of Johnson,isolated Fumic acid of Thenard, Lignoic acid of Hesse, Hymatomelanic acid of Hoppe - Seyler
  11. 11. Summary of Investigations – Second Phase1. Studies on Chemical Nature of HS2. Isolation of New HS – Crenic & Apocrenic Acids3. New Classification Schemes of HS1.HS – Chemically individual cpds2.Chemical nature, structure & properties not known3.Chemical methods to reproduce humification of plant materials
  12. 12. Second Half of 19th century Scientist ContributionEggerts, 1889 Crenic & Apocrenic acids natural products – criticized HA, UA & Humus CoalVan Bemmelen, complexity of chemical composition – HS1888 amorphous and colloidalBaumann, 1909 HS complex mixture of plant & animal residues in varying stages of decomposition – cannot be separatedBaumann & Gully, Acid nature of HS not due to functional1910 groups but colloidal propertiesLiebig, 1840 Mineral Nutrition theory as against humus theory – Humus only C source
  13. 13. Second Half of 19th century Scientist ContributionGrandeau, 1872 Mineral Humus Theories combined – Organo Mineral Plant Nutrition Theory – HS dominant role in dissolving, absorbing and exchange reactions in soilsPasteur, van Post,Humus not chemical or physical butDarwin, 1882,biological with diverse activities ofKostychev, 1886, microbes, protozoa, and various other89, Muller, 1887, organismRamann 1888Kostychev, 1890, Humus source of plant nutrients –Schloesing, 1902, promotes soil structure – favourable airDehrain, 1888, and water regimes in soilDehrain andDemoussy, 1896
  14. 14. Second Half of 19th century Contd. Scientist ContributionDokuchaev, 1883 “The Russian Chernozems”Kostychev, 1886 “Soils of the Chernozem of Russia” Biological Activity – Perennial Grassy Vegetation – Chernozem FormationSibirtzev, 1900 - 01 Role of Crenic and Apocrenic acids in podzol formationHoppe Seyler, 1889 Biochemistry of decomposition of some organic substancesOmelyansii, 1902 Biochemistry of decomposition of CelluloseVan Iterson, 1904 Anaerobic Decomposition of CelluloseSnyder, 1898 and Humification of isolated carbohydrates,Suzuki, 1906 – 08 oils and fats
  15. 15. Second Half of 19th century Contd. Scientist ContributionKostychev, 1886 HS formed by synthesis between proteinsHebert, 1892 and encrusting substancesDehrain, 1902Walksman, 1937 Lignoprotein complexes form the nucleus of humusSummary 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