This document provides information on the sulfur cycle. It discusses how sulfur is an essential nutrient for plants and occurs naturally in rocks, soil organic matter, and the atmosphere. The sulfur cycle involves four main processes: mineralization, immobilization, oxidation, and reduction. Sulfur cycles through these processes as it is released from rocks through weathering, taken up by plants and microbes, consumed by animals, and released again through decomposition. Key microbial actors like Thiobacillus bacteria are involved in oxidizing inorganic sulfur compounds in both aerobic and anaerobic conditions. The cycling of sulfur makes both organic and inorganic forms available to support life.

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
 Sulphur like N, is an essential element for all living systems
because of it’s
 inert nature, is not utilized by plants. To be used first S has to to
be oxidized or reduced.
 Only 1 to 3% of the soil total S is in the plant-available form
(SO42-).
 The bulk of soil S (200 to 1100 kg/ha) is in soil organic matter.
Mineralization of organic S compounds is an important source of
S for growing plants
 In soil, it occurs both organic (S containing amino acids, vitamins
) as well as inorganic forms (Sulphur, sulphates etc., )

3. What is Sulphur Cycle ?
Sulfur cycle, circulation of suphur in various forms through nature.
Sulphur occurs in all living matter as a component of
certain aminoaciods.
It is abundant in the soil in protiens and, through a series of
microbial transformations, ends up as sulphates usable by plants.

4. Process of sulphur cycle
 The sulphur is released by the weathering of rocks.
 Sulphur comes in contact with air and is converted into sulphates.
 Sulphates are taken up by plants and microbes and are converted
into organic forms.
 The organic form of sulphur is then consumed by the animals
through their food and thus sulphur moves in the food chain.
 When the animals die some of the sulphur is released by
decomposition while some enter the tissues of microbes.
 There are several natural sources such as volcanic eruptions,
evaporation of water, and breakdown of organic matter in swamps,
that release sulphur directly into the atmosphere. This sulphur falls
on earth with rainfall.

6. Cyclic transformation of S
There are four important processes under sulphur cycle:
1. Mineralization
2. Immobilization
3. Oxidation
4. Reduction

7. What are the steps of Sulphur cycle?
Four distinct transformations are recognized.
1. Decomposition/Mineralization of larger organic S
compounds to smaller units and their conversion into
inorganic compounds.
 2. Microbial associated immobilization
 3. Oxidation of inorganic ions and compounds such as
sulphides,thiosulphates, Sulphu
 4. Reduction of Sulphates and other sulphides

8.  The weathering of S-containing minerals such as gypsum
(CaSO4) can be a source of crop available S particularly in dry
regions where the amount of precipitation is too low to leach it
from the soil profile.
 Other primary and secondary minerals will release elemental S
(S0/S2-), which is converted to SO42- when exposed to moisture,
oxygen and microbial processes.

9. LeachCrop available S (sulphate -sulphur) can become
temporarily lost from soil solution through precipitation with
magnesium or calcium (typical for Alberta) or adsorption to
aluminum or iron oxides on clay particles.
Sulphate-sulphur is soluble and mobile in soils and will move with
groundwater.
ing losses of S are possible, especially in coarse textured soils,
but with average rainfall this type of loss will be low.
Volatile S losses can sometimes occur, but for most agricultural
soils these losses are thought to be insignificant.

10. Mineralization
 Conversion of organic bound S into inorganic state, mediated
through Microorganisms.
 The released S in either absorbed by plants or escaped into
atmosphere in the form of oxides.
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.  Produces Sulphuric acid ,lower down the soil pH – Hence used in
controlling
 plant disease
 Apple and Potato scab –Streptomyces scabis ,Sweet potato rot – S.
Ipomea
 S+ Thiobacillus application is used for the control
 Remediation of alkali soil
 Increases the solubilization of other nutrients (P,K,Ca,Mn,Al and Mg )
 Preparation of biosuper- Rock phosphate + T.thiooxidans and S---
Australia
 Lipman’s process- Compost preparation
 Soil + manure + elemental S + rock phosphate

12. Sulphate reduction
 Reduces inorganic sulphate into Hydrogen sulphide –reduces the
availability of S for plant nutrition.
 Sulphates are reduced to hydrogen sulphide by Desulfovibrio
desulfuricans. This occurs in two steps:
 Firstly, the sulphates are converted to sulphites utilizing ATP.
 Secondly, the reduction of sulphite to hydrogen sulphide.

13. THANK YOU