Soil Fertility and Nutrient management (1+1)

Sulphur Cycle and Transformation in soils

Sulphur Cycle in soil

S-Transformations In aerobic soil
The sulphur in soil is being cycled continuously between inorganic and organic forms just like Nitrogen. The nature of compounds formed and their transformations are influenced by the biologically mediated process. Organic matter is the major of source of S, it undergoes oxidation to SO42- . This is brought about by autotrophic bacteria belonging to the genus Thiobacillus under aerobic conditions of soil.

Aeration (O2)

Organic S ---------------------------> SO₄^2- + H+
(Proteins, Amino acids).
The released SO42- ion is taken up by plants and microorganisms. The rate of mineralization is affected by factors such as moisture (60% field capacity), aeration, temperature (35-40oC) and Soil pH.

In anaerobic soil
Under anaerobic conditions or flooded soils, the soil aeration is completely cut off. The SO42- ion is reduced to sulphides (S2-) by the autotrophic bacteria such as Desulpho vibrio and Desulpho maculans which use SO42- for their O2 requirements.

SO₄^2- + 8 H+ + 8^e- = S^2- + 4H₂O.