Soil fertility

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Microbial Mediated Micronutrient Transformation in soil

Microbial Mediated Micronutrient Transformation in soilFeZnCuMoMn

Plants require some elements in such minute or smaller amounts that these element have been designated as minor/trace element or Micro nutrient. Plants absorbed micronutrient in lower concentration ppm level.

MicronutrientIron, Zinc, Copper, Manganese, Boron, Molybdenum, Nickel, Chloride

Source- Goethite, Haematite, Magnetite, Limonite, OlivineForms of Fe- Ferrous & Ferric (Two oxidation state)Two fraction- Organic & mineral Sufficient range of Fe in plants : 50 250 ppm.Below 50 ppm Deficiency appears young leaves- Interveinal chlorosis.Above 250 ppm- Leaf bronzing.

Iron (Fe)

Fe in soilMineral Fe4th most abundant element in earth crust 5%Solubility is low.Soil solutionWell drained , oxidised soil has a more Fe3+Water logged soil More Fe2+

Iron bacteria (micro organisms) play a major role in transformation Bacteria & fungi oxidise ferrous state to ferric state.Heterotrophic microorganism attacks soluble organic Fe in to inorganic Fe salts.Bacteria & fungi produce specific enzyme.

Transformation of iron in soil by Micro organisms

Bacteria oxidise ferrous Fe to ferric Fe state which precipitate as ferric hydroxide Iron BacteriaGallinonellaSiderocapsaSiderosphaeraFerribacteriumNaumannielaSideromonasFerro-bacillusSiderobacterSiderococus

Obligate Chemoautotrophs- Capable of utilizing energy released in the process of ferric hydroxide formation.(E.g) Gallionella ferruginea Thiobacillus ferroxidans Ferrobacillus ferroxidans


Facultative Chemoautotrophs-Utilizing energy derived in the process of ferric hydroxide formation or from organic matter.(E,g) Leptothrix ochraceaeHeterotrophs- Do not energy derived in the process of ferric hydroxide formation but depend on organic matter for nutrition.(E.g) Naumanniela


Transform ferrous salts to ferric salt


Source: Limestone, Sandstone.Forms: Zn2+Sufficient range of Zn in plants : 25 150 ppmMineral: Zn in lithosphere is 80 ppmSoil solution: Depends on the soil pH . If pH is more Zn2+ availability is more.Zinc (Zn)

Two fractionOrganic- Small amount 0.01%- 0.05%Inorganic- Source is Zinc sulphate- soluble in soilBelow and above the range cause Rosetting or clustering of young leaves. Young leaves become chlorotic spot.

Omnipotent bacteria- Increase concentration of Zn Fungi also influence solubilize the mineral from of Zn in soil by production of organic acids.Organic material increase the availability of micro organisms in soil Increase the availability of Zn in soil Transformation of Zinc in soil by Micro organisms

Several zinc solubilizing bacteria (ZSB)- Tropical and temperate soils to provide plant available Zn. (Hafeez et al., 2013).Gluconacetobacter sugarcane. Bacillus, Pseudomonas - Soybean, rice and wheat capable of solubilizing Zn. (Saravanan et al., 2011). Omnipotent bacteria

Zinc solubilizing bacteriaPseudomonasBacillusGluconacetobacterBurkholderiaAcinetobacterSerratiaFlavobacter Enterobacter

ComparisonZSBZSB soil bacteria, able to solubilize the inorganic Zn

These ZSB strains produce variety of low molecular weight organic acids, particularly gluconic acid, dissolute the insoluble ZnReduce the pH of the soil solution - increase the plant available zinc (Hafeez et al., 2013). Zn-fertilizers - 1-5% use efficiency for most of the crops ZSB soil bacteria, able to solubilize the inorganic Zn and thereby increase the bioavailability for crop assimilation.

Source: Pyrolusite, Hausmannite, Manganite.Forms: Mn2+ Sufficient range of plant: 20 500 ppm.Fraction: Solution, Exchangeable, Organic, Mineral


Mineral MnMn is found in most Fe-Mg rocks- weathering of primary mineral.PyrolusiteManganiteSoil solution Mn:MnSO4 is the most common Mn sources in soil.Most common form Mn2+ - 90%. High pH- Solubility of Mn2+ is low

Manganese transformation include bacteria, fungi and yeasts. Bacteria Leptothrix mobilis - aquatic environment- oxidizing both iron, manganese. (Nelson et al. 1998)Oxidize manganous compounds to manganic oxides (MnO.,) at pH values as low as 6 & some times below 6. (Mulder 1964, Mulder and van Veen 1963).

Transformation of Manganese in soil by Micro organisms

Manganese oxidation by a mixture of two bacteria Corynebacterium sp. Chromobacterium sp. has been recorded by Bromfield and Skerman (1950) Roots of living plants may promote the solubilization of MnO, by excreting organic acids or other compounds stimulating bacterial activity.

Source: Malachite, Cupric ferrite, Carbonates, Silicates, Sulfates, Chlorides.Sufficient range in plants: 5 to 20 ppm.Forms: Cuprous (Cu+), Cupric (Cu2+) Copper

Availability of copper in soil related with the presence of black organic humus.H2S forming microorganisms may be involved in copper precipitation.

Transformation of Copper in soil by Micro organisms

Copper precipitation by hydrogen-sulphide-producing bacteria

Clostridia, Proteus vulgaris, Escherichia coli - producing H2S from sulphur-containing amino acids (cystine, methionine, glutathion, etc.)- precipitate the Cu Sulphate-reducing bacteria- precipitate the Cu- Insoluble form- Assimilatory sulfate reductionSulfate-reducing bacteria are responsible - hydrogen sulfide will react with metal ions to produce metal sulphides. These metal sulphides- insoluble

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