Soil Fertility and Fertilizers Use

1. Presentation
On
SULPHUR- SOURCE, FORMS, FERTILIZERS, THEIR BEHAVIOUR
IN SOILS, FACTORS AFFECTING THEIR AVAILABILITY
Soil Fertility & Fertilizer Use
SOILS- 502 (3+1)
Submitted by-
Abhishika Sonal John
M.Sc. Agronomy
S.G. College of Agriculture and Research Station, Jagdalpur

2. INTRODUCTION
• Sulphur is an essential secondary nutrient for the plants discovered
by Salon Horstmas.
• Sulphur is a major constituent of organic matter and involved in
enzymic processes.
• Sulphur is essential in the formation of plant protein because it is a
part of certain amino acids.
• It is an essential constituent of several other biologically active
compounds such as vitamins, acetyl coenzyme A, ferrodoxin,
glutathione etc.
• Many factors affect the availability of the 3 secondary nutrients in
plants which can be determined by soil analysis or combination of
soil and plant analysis.
• However, field observations and deficiency symptoms are also
important diagnostic tools.

3. CHARACTERISTICS OF SULPHUR NUTRIENT
 13TH most abundant element in earth crust.
 Atomic number- 16
 Atomic weight- 32.065
 % proportion of earth crust- 0.10%
 Ionic forms absorbed by plants- SO4
2- .
 Concentration of Sulphur in plant ranges from 0.1 to 0.5%.
 Mobility in plants- Relatively mobile.
 Deficiency symptoms appear first on younger leaves.
 Among the crop families Sulphur content increase in the order
Gramineae<Leguminosae<cruciferae.
 S content in soils: calcareous>peat>marsh>grey brown podzolic>
podzolic.
 SO4
2- is abundant in arid zones.

4. SOURCE OF SULPHUR NUTRIENT
• It occurs as sulphide in igneous and sedimentary rocks.
• The S- bearing minerals in rocks and soils are Gypsum (CaSO4. 2H2O), Epsomite
(MgSO4.7H2O), Mirabilite (Na2SO4.10H2O), Pyrite (FeS2), Chalcopyrite (CuFeS2),
Cobaltite (CoAsS) and Galena (PbS).
• Atmosphere is another source of sulphur.
• A considerable amount of Sulphur is released by the breakdown of the soil
organic matter that is 20-30 kg SO3 /ha.
• Cow and pig manure contains 1.8 kg SO3/t, compost contains around 3.8 kg
SO3/t and poultry manure contains around 8.3 kg SO3/t.
• Some mineral fertilizers also have sulphur content in the form of sulphate,
elemental sulphur and liquid form.
• Acid rain also provides Sulphur.

5. FORMS OF SULPHUR NUTRIENT IN SOIL
A. Inorganic form:
1.Readily soluble sulphates
2. Adsorbed sulphates
3. Insoluble sulphates
4. Co-precipitated with CaCO3
5. Reduced inorganic sulphur compounds (sulphide and elemental
sulphur)
B. Organic forms:
1.Hydroiodic acid (HI)reducible sulphur
2. Carbon bonded
3. Residual or unidentified sulphur

6. 1.Easily soluble sulphates
• Sulphur is usually taken by plants as the Sulphate ions.
• Concentration of 3 to 5 mg/kg SO4-S in the soil have been found adequate for
most plant growth.
• In sulphur deficient soils or soils having low sulphur supplying capacity the easily
soluble sulphate content lies between 5 and 10m g/kg.
• How ever the coarse textured soils like sandy and sandy loam soils are frequently
deficient in sulphur and contains sulphur less than 5 mg/kg.
• 2.Adsorbed sulphate
• It is an important fraction of sulphur in soils containing considerable higher amou
nts of hydrous oxides of Fe and Al. As for example,ultisols,oxisols and alfisols
• contribute significantly to the sulphur requirement of crops grown in highly
weathered soils .
• It has also been found that the concentration of this fraction is found higher at
depths ranging from 15 to 75cm below the surface.
• Adsorbed sulphate can account for up to one third of total in sub soils, while the
same fraction represents less than 10% of the total sulphur in the surface soil.

7. 3. Sulphate co-precipitated with calcium carbonate and other precipitated forms.
• Mostly found in calcareous soils particularly when calcium carbonate is present as
its coarse particles.
• This fraction is relatively available to plants.
4. Reduced inorganic sulphur
Under water logged conditions, sulphide fraction is known to be dominant resulting from
the reduction of sulphate .
• a)Sulphide form
• under flooded as well as an intense anaerobic soil conditions
• How ever the magnitude of such accumulation may be greater in soils containing higher
amount of organic matter.
• How ever there may be little or no accumulation of sulpide at Eh>-150mv and pH range
between 6.5 to 8.5
• b)Elemental sulphur
• it is an intermediate product of oxidation process of sulphide.
• How ever this form of sulphur may form in soils of incomplete oxidation of sulphur due to
alternate flooding.

8. 1. HI reducible (non-carbon bonded) sulphur
• Sulphur in this pool is extracted using hydroiodic acid and this fraction of sulphur is not
bonded to carbon.
• This form of sulphur is largely present as sulphate esters and ethers with C-O-S linkage.
• Out of the total organic sulphur about half is present in this fraction.
2.Carbon bonded sulphur
• In this fraction sulphur is directly bonded to carbon and this fraction is determined by the
reduction to sulphide with Raney nickel.
• This fraction of sulphur consisting of sulphur containing amino acids,cystine and
methionine, amounting about 20%of total organic sulphur.
• In addition some other form of sulphur like sulphoxide,sulphenic,sulphinic,and sulphonic
acids and some heterocyclic compounds are present in this form.
3.Residiual or un identified
When organic sulphur is not extracted by either by HI or Raney nickel it is considered as
residual or unidentified. This accounts for 30-40%of total organic sulphur. since it is a most
stable form of sulphur, it has a very little practical implication in plant nutrition.

9. SULPHUR FERTILIZERS

10. BEHAVIOUR OF SULPHUR FERTILIZERS IN SOIL
1. MINERALIZATION
• All the forms of Sulphur are not available to the crop plants, therefore, its
mineralization is essential to convert unavailable form of sulphur into available
form.
• Organic matter is the major source of soil S and its oxidation to SO4
2- is
brought about by microorganisms and this process is called mineralization.
• It is evident that smaller amount of inorganic sulphate is released from the
organic materials containing low amount of initial sulphur content (less than
0.15%) because of immobilization of sulphur.
• Rate of mineralization is affected by factors such as:
 Moisture
 Temperature
 Aeration
 Soil pH

11. 2. IMMOBILIZATION
• Under limited S supply and excess of carbonaceous materials, the mineralized S
can be readily used by the microorganisms. Hence, crop plants may suffer from
S- deficiency. This process is called “immobilization”.
• Immobilization is a temporary phase.
• Immobilization of sulphur takes places in soil when the ratio of either C or N to S
is very wide.
• If C/S weight ratio is at or below 200:1,then mineralization of sulphur takes
place and above this ratio, immobilization occurs that means most of the
sulphate is associated with the organic forms like humus, microbial cells and by
products of microbial synthesis.

12. 3. OXIDATION – REDUCTION REACTION
• Since, S exists in more than one oxidation states it is subjected to the oxidation- reduction
reactions in the soil.
• These reactions are biochemical in nature and are mediated by autotrophic bacteria of
the genus Thiobacillus.
• Under anaerobic conditions, when the availability of free air is completely cut off like in
marshylands and lowland rice fields, partially oxidized chemicals such as NO3 - and SO4 2-
are reduced and utilized by microorganisms such as Desulphovibrio and
Desulphotomaculum.
• In the process these ions are reduced to nitrites, nitrous oxides, sulphites and sulphides.
• In the reduction- oxidation process SO4 2- is the last ion to undergo reduction after all the
nitrate, Mn(IV), Fe(III) ions have been reduced. This means intense reduction conditions
are required before SO4 2- is reduced.
• During decomposition of organic matter under normal arable farming conditions, organic
sulphur compounds are transformed/ oxidized into sulphates. The intermediate products
of this transformation are sulphides, thiosulphates and polythionates.
• Oxidation reactions in soils are biochemical in nature.

13. FACTORS AFFECTING AVAILABILITY OF SULPHUR
1. Type and amount of clay
The availability decreases in soil having high amount of clay
because of the retention of the soluble sulphate by the clay
minerals due to adsorption mechanism. Seen more in 1:1 type
clay minerals.
2. Oxides and hydroxides of Fe and Al
Substantial amount of sulphate is also retained on the surface
making it unavailable. Especially seen in Ultisols, Alfisols and
Oxisols.
3. pH
In strong acid soils the availability of Sulphur decreases because
of higher retention through adsorption. In general oxidation of
sulphur takes place rapidly under acidic soil, because optimum pH
range for the activity of Thiobacillus sp. in carrying out oxidation
process is 4 to 7.2. However, the amount of released sulphur is
directly proportional to soil pH up to value of 7.5

14. 4. Organic matter
Soil containing higher amount of organic matter ,have higher ability
to supply sulphur to plant because of greater release of sulphate
sulphur releasing from the mineralization process.
5. Cations and anions
Various cations like H,K,Ca,Mg and Na and anions like OH-,PO4
3-,NO3
-
,Cl- etc. Affect the availability of sulphate sulphur in soils through
adsorption mechanism. Example, acid soils containing higher amount
of H+ retain a greater amount of sulphate where as, soils fertilized
with sufficient amount of phosphorus reduce the sulphate adsorption
with subsequent release of sulphate in soil solution.
6. Presence or absence of vegetation
A greater amount of sulphur is mineralized in cropped than that of
uncropped soils.

15. 7. Alternate wetting and drying
Variation in soil moisture ranging from field capacity to saturation
affects the mineralization of sulphur mainly ester sulphates in soil
organic matter. Drying after soil saturation or submergence, reduce
the sulphur content in the soils .
8. Interaction of sulphur with other nutrients
• The interaction of N with S is found to be synergistic.
• A similar positive interaction has found between S and P.
• The application of Zn increased the utilization of sulphur by crops
• However the combination with other nutrients like Mo, B, Se
affect the availability of both native and applied sulphur.

16. CONCLUSION
• Sulphur is essential in plant nutrition and its deficiency can seriously affect the
growth, yield and the quality of the crops and produce.
• Sulphur deficiency is widespread on coarse textured low organic matter soils. Such
soils need to be managed for sulphur fertility.
• Significant residual effect observed for sulphur can be positively exploited for
increasing yield and quality of products especially in pulses and oilseeds.
• Soil- test based site specific management of secondary nutrients not only improves
yield but also the quality of fruits, vegetables and oilseeds.
• In precision agriculture the soluble sources of the secondary nutrients can be
applied through fertigation and foliar application to supplement these nutrients.