Transformation of Nitrogen, Phosphorous, Potassium and Sulphur

Transformation of Nitrogen, Phosphorous, Potassium and Sulphur

1. ASSIGNMENT ON Transformation of N itrogen , Phosphorous, Potassium and Sulphur College of Agriculture, Raipur INDIRA GANDHI KRISHI VISHWAVIDYALAYA, RAIPUR SUBMITTED TO- Dr. R.N. SINGH Professor SOIL SCIENCE AND AGRICULTURAL CHEMISTRY PRESENTED BY- DEEPIKA SAHU Ph.D. 1 st year 1 st semester Department- Soil Science and Agricultural Chemistry

2. CONTENT Introduction Nitrogen Transformations Forms and Fate of Nitrogen in Soil Phosphorous Transformation Potassium Transformation P otassium mobilizers Sulphur transformation Sulphur mobilizing microbes Conclusion REFERENCE

3. Nitrogen Transformation

4. Nitrogen Transformations in Soil Plants absorb most of the N in the HN 4 + and NO 3 - forms. Nitrate is the dominant source as its concentration is higher than HN 4 + and it is free to move to the roots. Potatoes, sugar beet, pine apple, prefer both the forms; tomatoes, celery, bush beans, prefer NO 3 - , rice and blue berries prefer HN 4 + . NO 3 - -N uptake is usually high and is favored by low pH conditions. HN 4 + -N is less subjected to losses by leaching and denitrification. HN 4 + uptake is best at neutral pH values. When the plants are supplied with HN 4 + -N, it leads to acidity in the soil.

5. Forms and Fate of Nitrogen in Soil There are three major forms or states of nitrogen in soil: organic nitrogen (Org-N), ammonium nitrogen ( HN 4 + -N), and nitrate nitrogen ( NO 3 - -N). Plants cannot use the nitrogen in the organic form. Plants can only use ammonium and nitrate forms of nitrogen. Microbes are constantly metabolizing and recycling nitrogen as they breakdown organic matter. Mineralization occurs when organic nitrogen is broken down to form ammonium nitrogen, which is available for plant use. Nitrification occurs as ammonium is further changed by microorganisms to the nitrate form, also available to plants. The rate at which nitrogen becomes available is determined by the complexity and stability of the organic matter and by microbial activity. It may occur in days or, if the nitrogen is in a very stable form, it may take years.

6. Organic Nitrogen is nitrogen contained in organic matter. For example it includes proteins, organic acids, and DNA as well as more complex organic molecules. Organic matter must be broken down by soil microbes to release nitrogen in forms that plants can use . In general, conditions that are good for microbial activity, such as warm and moist. soil, will promote more rapid breakdown of organic nitrogen. However, some organic nitrogen is in forms that are difficult for microbes to digest and release under any circumstances. For this reason it is hard to predict how much and when plant-available nitrogen will be released from organic matter. The majority of manure nitrogen is usually released in the first year of application but additional nitrogen will become available in subsequent years.

7. Mineralization of N compounds: N mineralization is simply the conversion of organic nitrogen to mineral form (NH 4 + , NO 3 - , and NO 2 - ). When organic residues having a C: N ratio wider than 30 are added to the soil, immobilisation of nitrogen takes place. If C:N ratio is narrow i.e. , less than 20 (for legume residues), mineralisation is the result. It takes place essentially by three steps. 1. Aminisation 2. Ammonification 3. Nitrification. Aminisation : Heterotrophic soil microbes, mostly, bacteria like Pseudomonas and Bacillus are believed to dominate in the break down of proteins in neutral and alkaline soils. Under acidic conditions fungi prevail. In this step hydrolytic decomposition of proteins and release of amines and amino acids takes place. Proteins R-NH 2 + CO 2 + Energy + other products. Ammonification :  refers to any chemical reaction in which NH 2  groups are converted into ammonia or its ionic form, ammonium (NH 4 + ), as an end product. Bacteria and related microorganisms derive metabolically useful energy from the oxidation of organic nitrogen to ammonium.

8. Nitrification : The biological oxidation of NH 4 + released by the process of ammonification to nitrate is known as nitrification. This process is carried out by nitrifying bacteria referred to as nitrifiers . It is a two step process in which NH 4 + is first converted to nitrite ( NO 2 - ) and then to nitrate ( NO 3 - ). Conversion to nitrite is brought about largely by a group of obligate autotrophic bacteria known as Nitrosomonas as: 2 NH 4 + + 3 O 2 2 NO 2 - + 2 H 2 O + 4H + The conversion from nitrite to nitrate is affected by Nitrobacter as follows : 2 NO 2 - + O 2 2 NO 3 -

9. DENITRIFICATION- An additional potential fate for nitrate nitrogen under specific field conditions is its conversion to nitrogen gas (N 2 ) through a process called denitrification. This occurs when soil is totally saturated by flooding and no oxygen is present. When these conditions occur, specialized microbes convert nitrate, through a series of steps, into nitrogen gas. The nitrogen gas can then move up through soil and into the atmosphere, which is composed mostly of nitrogen. Thiobacillus denitrificans , Micrococcus denitrificans ,  and some species of  Serratia , Pseudomonas,  and  Achromobacter  are implicated as denitrifiers .  Pseudomonas aeruginosa can, under anaerobic conditions (as in swampy or water-logged soils), reduce the amount of fixed nitrogen (as fertilizer) by up to 50 percent.

10. Heterotrph , Obligate anaerobic free- living nitrogen fixers Clostridium Desulfovibrio Desulfotomaculum Hetertrophic , facultative anaerobic and free- living nitrogen fixers Bacillus Citrobacter Klebsiella Non Symbiotic N fixers Aerobic Chemo- heterotroph free living Chemoheterotrauph associated to living (rice, millet) Beijerinckia Clostridium Cyanobacteria Anaebina Nostoc Derxia Azotobactor Azospirillum Denitrifiers Thiobacillus denitrificans Micrococcus denitrificans Pseudomonas  Achromobacter Pseudomonas aeruginosa

11. PHOSPHOROUS TRANSFORMATION

12. Microbes play a fundamental role in mobilizing organic, native or inherited P that unavailable for plants. The total P acquired by plants through bacteria and fungus (75%). Biochemical processes operating in the rhizosphere determine the mobilization and acquisition of soil nutrients. Wide variety of bacteria, fungi and endophytes solubilize insoluble P through the production of organic acids, a feature which is genetically controlled. Such type of inocula are termed as P-mobilizing microbes, as these inocula do not only solubilize P, but they also mobilize its organic form through mineralization and facilitate the translocation of phosphate.

13. Phosphorus is only second to nitrogen as a mineral nutrient required for plants, animals and microorganisms. It is a major constituent of nucleic acids in all living systems essential in the accumulation and release of energy during cellular metabolism. This element is added to the soil in the form of chemical fertilizers, or in the form of organic phosphates present in plant and animal residues. Only 15 % of total soil phosphorus is in available form. Both inorganic and organic phosphates exist in soil and occupy a critical position both in plant growth and in the biology of soil.

14. ORGANIC P Mobilization Direct way Lowering pH Hydrolyze organic P Indirect way Release CO2 Release of proton Bacillus Beijernckia Burkholderia Enterobacter Flavobacterium Microbacterium Pseudomons Mesorhizobium cicero Mesorhizobium mediterraneum Aspergillus Penicillium

15. Microorganisms are known to bring a number of transformations of phosphorus, these include: Altering the solubility of inorganic compounds of phosphorus, Mineralization of organic phosphate compounds into inorganic phosphates, Conversion of inorganic, available anion into cell components i.e. a n immobilization process and o xidation or reduction of inorganic phosphorus. Compounds o f these mineralization and immobilization are the most important reactions /processes in phosphorus cycle.

16. Insoluble inorganic compounds of phosphorus are unavailable to plants, but many microorganisms can bring the phosphate into solution. Soil phosphates are rendered available either by plant roots or by soil microorganisms through secretion of organic acids ( e.g. lactic, acetic, formic, fumaric , succinic acids etc ). Thus, phosphate dissolving / solubilizing soil microorganisms ( e.g . species of  Pseudomonas, Bacillus, Micrococcus, Mycobacterium, Flavobacterium , Penicillium , Aspergillus , Fusarium   etc. ) plays important role in correcting phosphorus deficiency of crop plants. Solubilization of phosphate by plant roots and soil microorganisms is substantially influenced by various soil factors, such as pH, moisture and aeration. In neutral or alkaline soils solubilization of phosphate is more as compared to acidic soils.

17. Mineralization is favored by high temperatures ( thermophilic range) and more in acidic to neutral soils with high organic phosphorus content. The enzyme involved in mineralization (cleavage) of phosphate from organic phosphorus compound is collectively called as  “ Phospatases " . The commercially used species of phosphate solubilizing bacteria and fungi are:  Bacillus polymyxa , Bacillus megatherium . Pseudomonas strita , Aspergillus , Penicllium avamori and Mycorrhiza . P solubilizing Organisms Bacteria Psuedomonas striata Bacillus megatherium Fungi Aspergillus niger Penicillium biloji

18. K TRANSFORMATION Fig.- Interrelationships of various forms of soil K (Sparks and Huang, 1985 )

19. K is present in very small amount ranging from 0.04 to 3.00 %. Despite of being in limited amount, 98% of this K is bound within the Phyllosilicates structures. The remaining 2% exists in soil solution or on exchange sites to become available for the plants. Hence, soil fertility is decreased due to low availability of this nutrient. Many microorganism in the soil are able to solubilize unavailable forms of K- bearing minerals, such as micas , feldspar , illite and orthoclases by excreting organic acids which either directly dissolves rock K or chelate silicon ions to bring the K into solution.

20. Potassium (K) is considered as an essential nutrient and a major constituent within all living cells. Naturally, soils contain K in larger amounts than any other nutrients; however most of the K is unavailable for plant uptake. Application of chemical fertilizers has a considerably negative impact on environmental sustainability. It is known that potassium solubilizing bacteria (KSB) can solubilize K-bearing minerals and convert the insoluble K to soluble forms of K available to plant uptake.

21. Many bacteria such as  Acidothiobacillus ferrooxidans ,   Paenibacillus  spp.,  Bacillus mucilaginosus , B. edaphicus ,  and  B. circulans  have capacity to solubilize K minerals ( e.g ., biotite , feldspar, illite , muscovite, orthoclase, and mica). KSB are usually present in all soils, although their number, diversity and ability for K solubilization vary depending upon the soil and climatic conditions. KSB can dissolve silicate minerals and release K through the production of organic and inorganic acids, acidolysis , polysaccharides, chelation , and exchange reactions.

22. Frateuria sp. Acidothiobacillus ferrooxidans Bacillus mucilaginosus B. edaphicus Burkholderia sp. Pseudomonas sp. Rhizobium sp. Funneliforms mosseae Rhizoglomus intraradices Aspergillus terreus A. niger Cupriavidus necator Cupriavidus necator K mobilizers

23. Sulphur cycle / sulphur transformation:- Sulpher is the most abundant & widely distributed element in the nature and found both in free as well as combined states. In the soil S is in the organic form( sulpher containing amino acid, cystine , mithionine , proteins, polypeptides, biotin, thiamin etc. ) which is metabolized by soil microorganism to make it available in an inorganic form(sulpher, sulphate, sulphite , thiosulphate etc) for plant nutrition . The total S present in soil only 10 to 15% is in the inorganic form (sulphate ) and about 75 to 90% i s in organic form .

24. In agricultural soil, most of the Sulphur ( >95% ) is present as sulphate esters or as carbon bounded Sulphur rather than inorganic Sulphur . The two major form of organic-S, Sulphur-esters and sulfonates are not directly available to plants which rely upon microbes in soil and rhizosphere for organo ic S mobilization . Different Sulphur forms are interconverted and immobilized Sulphur is mineralized to yield plant available inorganic Sulphur . Organic form of Sulphur is metabolized by soil microorganism to make it available for plant in an inorganic form like mineralization, immobilization, oxidation and reduction .

25. Lolium perenne Enterobacter Serratia Comamonas Pseudomonas Klebsiella Salmonella Sulphur mobilizing microbes

26. Transformation of S between organic & elemental states and between oxidized & reduced states is brought about by various micro organisms, specially bacteria . The major steps of transformation involved in the cycling of S are:- Mineralization Immobilization Oxidation Reduction

27. Mineralization:- T he breakdown/ decomposition of large organic sulphur compound to smaller units and their conversion into inorganic compound (sulphate). The process of such mineralization is a microbial & hence any factor which can affect the growth & activity of concerned micro organisms ultimately modify the mineralization of sulpher. The rate of Sulphur mineralization is about 1 to 10%/year.

28. Immobilization M icrobial conversion of inorganic S compound to organic S compounds. Immobilization occur with wide C/S ratios because of conversion of a large amount of carbon into microbial biomass with a resultant higher requirement for Sulphur . Sulphur oxidation When plant & animal protein are degraded, the sulphur is released from the amino acid and accumulated in the soil which is then oxidized to sulphate in the presence of oxygen.

29. Under anaerobic condition (water logged soil) organic sulpher is decomposed to produce hydrogen sulphide ( H 2 S ) can also accumulate during the reduction of sulphates under anaerobic conditions which can be further oxidized to sulphates under aerobic condition. Oxidation of elemental S , sulphides ,& other inorganic S compounds take place both chemical & biological processes. The chemical process is very slow & hence it is little importance in S oxidation as compared to microbial process of S oxidation . By the action of soil micro organism ( thiobacillus sp .) oxidation S S O 4

30. Oxidation of elemental S & inorganic sulpher compounds (such as H 2 S , sulphide & thiosulphate ) to sulphate ( SO 4 - ) is brought about by chemoautotrophic and photosynthetic bacteria. S oxidation mediated by chemolithotrophs using reduced S compounds as e- donors reaction mediated by Thiobacillus thiooxidans is : HS - + O 2 ---> SO 4 -2 + H +  G' o = - 46 Kj

31. The members of genus thiobacillus ( obligate chemolithotrophic , nonphotosynthetic). e.g .- T.ferrooxidence and T.thiooxidence are the main organisms involved in the oxidation of elemental sulpher to sulphates these are aerobic non filamentous , chemosynthetic autotrophs . Other than thiobacillus heterotrophic bac . ( bacillus, pseudomonas and arthobacter ) & fungi ( aspergillus , penicillum ) & some actinomycetes are also reported to oxidized sulphur compound. Green & purple bacteria ( photolithotrophs ) of genera ( chlorobium , chloromatium , rhodopseudomonas ) are also reported to oxidized sulphur in aquatic environment .

32. Reduction of sulphate — Sulphate in the soil is assimilated by plants & micro organism and incorporated in to proteins. This is known as assimilatory “sulphate reduction”. Sulphate can be reduced to H 2 S by sulphate reducing bacteria ( e.g. Desulphovibrio & Desufatomacultum ) & may diminish the availability of S for plant nutrition . Sulphate reduction is favor by the alkaline & anaerobic condition of soil & sulphate are reduced to H 2 S .

33. Example: Calcium sulphate is attacked anaerobic condition by the members of genus Desulfovibrio & Desulfamaculatum to release H 2 S , . CaSO 4 + 4H 2 O ---  ca(OH) 2 + H 2 S , + H 2 O H 2 S produced by the reaction of sulphate & sulphur containing amino acid decomposition is further oxidized by some spp. of green & purple phototrophic bacteria ( e.g . Cholorobium , chromatium ) to release elemental S. CO 2 + 2 H 2 S ---(CH 2 O) + H 2 O + 2S The predominant S – reducing bacteria genera in soil are desulphovibrio , desulfamaculatum & desulfomonas (all obligate anaerobes).

34. Table: Selected examples of microbial mediated soil transformation that influence the plant nutrient availability Nutrient Microbial transformation Nitrogen Mineralization, Immobilization, nitrification, denitrification, urea hydrolysis, N₂ fixation, extracellular protease and chitinase activity Phosphorus Mineralization, immobilization, extracellular phosphatase activity, acidic dissolution of mineral P , facilitated uptake mycorrhizal fungi Potassium K solubilization/Mobilization Sulfur Mineralization, immobilization, oxidation, reduction, extracellular sulfatase activity

35. The microbes play a vital role in nutrient mobilization, transformation and fertilizer use efficiency are evident by many case studies, without them or their activities stated for different natural biological processes and the crop growth remains low. Microbial inoculant’s actions in rhizosphere directly helps for the nutrient accessibility viz . N, P, K, S in soil by taking part in nutrient dynamics and ultimately to achieve the important goal of agriculture to harvest better crop yield and to keep soil healthy and living for a long run in sustained manner . Conclusion

36. http://sulphur cycle.oeg.pdf.defpl.com. www.fem,mn,transforme.oeg.com.in . www.wikipedia.com . Das, D.K.1996. Introductory Soil Science. Kalyani Publishers, New Delhi.pp . 293-314. Rattan, R.K. Katyal , J.C., Dwivedi , B.S., Sankar , A.K., Bhattacharyya, Tapas, Tarafdar , J.C. and Kukal , S.S. 2015. Soil Science: An Introduction. Indian Society of Soil Science, New Delhi. pp. 465. REFERENCE