-Sulphur cycle.ppt

Bihar agricultural College

1. KASTURIKA SEN BEURA
Asstt. Professor-cum-Junior Scientist
UG Class Lecture
on
Sulphur Cycle
(for ASC-121)
DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY
BIHAR AGRICULTURAL UNIVERSITY, SABOUR,
BHAGALPUR-813210

2. Importance of Sulphur
SulphurlikeN,isanessentialelementforalllivingsystems
becauseofit’s
inertnature,isnotutilizedbyplants.TobeusedfirstShastoto
beoxidizedorreduced.
Only1to3%ofthesoiltotalSisintheplant-availableform
(SO
42-).
ThebulkofsoilS(200to1100kg/ha)isinsoilorganicmatter.
MineralizationoforganicScompoundsisanimportantsourceof
Sforgrowingplants
Insoil,itoccursbothorganic(Scontainingaminoacids,vitamins
)aswellasinorganicforms(Sulphur,sulphatesetc.,)

3. What is SulphurCycle ?
Sulfurcycle,circulationofsuphurinvariousformsthroughnature.
Sulphuroccursinalllivingmatterasacomponentof
certainaminoaciods.
Itisabundantinthesoilinprotiensand,throughaseriesof
microbialtransformations,endsupassulphatesusablebyplants.

4. Process of sulphur cycle
Thesulphurisreleasedbytheweatheringofrocks.
Sulphurcomesincontactwithairandisconvertedintosulphates.
Sulphatesaretakenupbyplantsandmicrobesandareconverted
intoorganicforms.
Theorganicformofsulphuristhenconsumedbytheanimals
throughtheirfoodandthussulphurmovesinthefoodchain.
Whentheanimalsdiesomeofthesulphurisreleasedby
decompositionwhilesomeenterthetissuesofmicrobes.
Thereareseveralnaturalsourcessuchasvolcaniceruptions,
evaporationofwater,andbreakdownoforganicmatterinswamps,
thatreleasesulphurdirectlyintotheatmosphere.Thissulphurfalls
onearthwithrainfall.

6. Cyclic transformation of S
Therearefourimportantprocessesundersulphurcycle:
1.Mineralization
2.Immobilization
3.Oxidation
4.Reduction

7. What are the steps of Sulphurcycle?
Fourdistincttransformationsarerecognized.
1.Decomposition/MineralizationoflargerorganicS
compoundstosmallerunitsandtheirconversioninto
inorganiccompounds.
2.Microbialassociatedimmobilization
3.Oxidationofinorganicionsandcompoundssuchas
sulphides,thiosulphates,Sulphu
4.ReductionofSulphatesandothersulphides

8. TheweatheringofS-containingmineralssuchasgypsum
(CaSO
4)canbeasourceofcropavailableSparticularlyindry
regionswheretheamountofprecipitationistoolowtoleachit
fromthesoilprofile.
OtherprimaryandsecondarymineralswillreleaseelementalS
(S0/S2-),whichisconvertedtoSO
42-whenexposedtomoisture,
oxygenandmicrobialprocesses.

9. LeachCropavailableS(sulphate-sulphur)canbecome
temporarilylostfromsoilsolutionthroughprecipitationwith
magnesiumorcalcium(typicalforAlberta)oradsorptionto
aluminumorironoxidesonclayparticles.
Sulphate-sulphurissolubleandmobileinsoilsandwillmovewith
groundwater.
inglossesofSarepossible,especiallyincoarsetexturedsoils,
butwithaveragerainfallthistypeoflosswillbelow.
VolatileSlossescansometimesoccur,butformostagricultural
soilstheselossesarethoughttobeinsignificant.

10. Mineralization
ConversionoforganicboundSintoinorganicstate,mediated
throughMicroorganisms.
ThereleasedSineitherabsorbedbyplantsorescapedinto
atmosphereintheformofoxides.
Oxidation
Occurs both in aerobic and anaerobic condition
• Bacteria
• Nonfilamentous forms-Thiobacillus
• Filamentous forms –Beggiatoa,Thiothrix and Thioloca
• Fungi and actinomycets
• Aspergillus, Penecillium and Microsporium

11. ProducesSulphuricacid,lowerdownthesoilpH–Henceusedin
controlling
plantdisease
AppleandPotatoscab–Streptomycesscabis,Sweetpotatorot–S.
Ipomea
S+Thiobacillusapplicationisusedforthecontrol
Remediationofalkalisoil
Increasesthesolubilizationofothernutrients(P,K,Ca,Mn,AlandMg)
Preparationofbiosuper-Rockphosphate+T.thiooxidansandS---
Australia
Lipman’sprocess-Compostpreparation
Soil+manure+elementalS+rockphosphate

12. Sulphatereduction
ReducesinorganicsulphateintoHydrogensulphide–reducesthe
availabilityofSforplantnutrition.
SulphatesarereducedtohydrogensulphidebyDesulfovibrio
desulfuricans.Thisoccursintwosteps:
Firstly,thesulphatesareconvertedtosulphitesutilizingATP.
Secondly,thereductionofsulphitetohydrogensulphide.

13. THANK YOU