This document discusses the transformation of nitrogen, phosphorus, potassium, and sulfur in soils. It describes the key processes involved in each transformation, including mineralization, nitrification, denitrification, immobilization, solubilization, and oxidation/reduction. It notes that microorganisms play a critical role in transforming organic forms of nutrients into plant-available inorganic forms through the secretion of enzymes and organic acids. Specific microbes involved in each transformation are also outlined, such as nitrifying bacteria, phosphate solubilizing bacteria and fungi, potassium solubilizing bacteria, and sulfur oxidizing bacteria.

1. ASSIGNMENT ON
Transformation of Nitrogen, 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. 1st year 1st semester
Department- Soil Science and
Agricultural Chemistry

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

3. Nitrogen
Transformation

4. Nitrogen Transformations in Soil
•Plants absorb most of the N in the HN4
+ and NO3
- forms.
Nitrate is the dominant source as its concentration is higher
than HN4
+ and it is free to move to the roots. Potatoes, sugar
beet, pine apple, prefer both the forms; tomatoes, celery, bush
beans, prefer NO3
- , rice and blue berries prefer HN4
+.
• NO3
--N uptake is usually high and is favored by low pH
conditions. HN4
+-N is less subjected to losses by leaching and
denitrification. HN4
+ uptake is best at neutral pH values. When
the plants are supplied with HN4
+-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 (HN4
+-N), and nitrate nitrogen
(NO3
--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 (NH4
+, NO3
-, and NO2
-). 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-NH2 + CO2 + Energy + other products.
• Ammonification: refers to any chemical reaction in which
NH2 groups are converted into ammonia or its ionic form, ammonium
(NH4
+), as an end product. Bacteria and related microorganisms derive
metabolically useful energy from the oxidation of organic nitrogen to
ammonium.

9. • Nitrification : The biological oxidation of NH4
+
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 NH4
+ is first converted to nitrite
(NO2
-) and then to nitrate (NO3
-). Conversion to nitrite
is brought about largely by a group of obligate
autotrophic bacteria known as Nitrosomonas as:
2 NH4
+ + 3 O2 2 NO2
- + 2 H2O + 4H+
• The conversion from nitrite to nitrate is affected by
Nitrobacter as follows :
2 NO2
- + O2 2 NO3
-

11. DENITRIFICATION-
An additional potential fate for nitrate nitrogen under
specific field conditions is its conversion to nitrogen gas
(N2) 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.

12. •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

13. PHOSPHOROUS TRANSFORMATION

14. 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.

15. • 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.

16. 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

17. 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. an immobilization process and
oxidation or reduction of inorganic phosphorus.
 Compounds of these mineralization and
immobilization are the most important reactions
/processes in phosphorus cycle.

18. • 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.

20. • 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

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

22. 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.

23. 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.

24. 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.

25. 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

26. 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% is in organic form.

27. •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 organoic 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.

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

29. 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:-
1) Mineralization
2) Immobilization
3) Oxidation
4) Reduction

30. Mineralization:-
The 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.

31. Immobilization
 Microbial 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.

32. Under anaerobic condition (water logged soil) organic sulpher
is decomposed to produce hydrogen sulphide (H2S) 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 SO4

33. Oxidation of elemental S & inorganic sulpher
compounds (such as H2S, sulphide & thiosulphate) to
sulphate (SO4
-) 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- + O2 ---> SO4
-2 + H+ G'o = - 46 Kj

34. 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.

35. 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 H2S 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
H2S.

36. Example: Calcium sulphate is attacked anaerobic condition by
the members of genus Desulfovibrio & Desulfamaculatum to
release H2S, .
CaSO4+ 4H2O --- ca(OH)2 + H2S, + H2O
H2S 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.
CO2+ 2 H2S ---(CH2O) + H2O + 2S
The predominant S – reducing bacteria genera in soil are
desulphovibrio, desulfamaculatum & desulfomonas (all
obligate anaerobes).

37. 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, extracellularproteaseandchitinaseactivity
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
sulfataseactivity

38. 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

39. •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