Background: Sulphur is rapidly being recognized as fourth key nutrient for plants after nitrogen, phosphorus and potassium. It functions in several critical metabolic and physiological processes, such as Chlorophyll synthesis, Protein synthesis, Activation of enzymes, Stress tolerance and Seed production. This study was carried to investigate the effect of synthesized nano sulphur in combination with organic amendment to study available sulphur status in calcareous soil. 
 
Methods: Nano sulphur was synthesized using reverse microemulsion (water-in-oil microemulsion) technique and characterized at the Centre for Agricultural Nanotechnology, TNAU, Coimbatore. An incubation experiment was carried out with synthesized nano sulphur and gypsum as sulphur source with and without FYM to determine sulphur release at various intervals (7th,15th,30th,45th&nbsp;and 60th&nbsp;days after incubation). 
 
Result: It was observed that nano sulphur applied at 40 kg S ha-1 with FYM showed high release of sulphur in calcareous soil in all intervals analysed during the experiment. The addition of organic manures aids in proliferation of heterotrophic sulphur oxidising bacteria which enhances the sulphur oxidation in alkaline soil.

Characterization and Assessment of Synthesized Nano Sulphur in Combination with Organic Amendment on the Availability of Sulphur in Calcareous Soil