The Study of Elemental Sulfur Oxidation and Its Relation to Some Nutrients Release in Wheat Cultivated Calcareous Soils.

The conjunction of calcareous parent materials and dry climate has resulted in the development of calcareous and alkali soils in large areas of Iran. Due to the high levels of Ca++ in soil solutions and high pH values, the soil nutrients, whose absorptions depend on pH, will become less available and thus limit the growth of crop plants. It has been a common practice in many regions of the world to use elemental sulfur as an acidifying source to lower pH and to improve the availability of some soil nutrients. In addition, the supply of sulfur used for the reclamation of sodium affected soils serves as a source of plant nutrient and more importantly acts as a disease controlling agent. Sulfur application in agricultural practices deserves more consideration especially, since a large quantity of this material is produced in the country, where a great percentage of the farmlands are calcareous. A major requirement in utilizing elemental sulfur to lower soil pH is the presence and activity of sulfur oxidizing bacteria (especially the Thiobacilli) in the soils. The beneficial effects of sulfur application along with Thiobacillus bacteria for soil reclamation and improvement of soil nutrient availability have been demonstrated in various fields as well as greenhouse studies. About the use elemental sulfur as an acidifying source to lower pH and to improve the availability of some soil nutrients in calcareous and alkali soils many researches have been done. But there are few information in the case of factore affecting sulfur efficiency such as amounts and time of sulfur application as well soil lime content and relation between them and applied sulfur. So The objectives of this research were to evaluate the effects of Thiobacilli bacteria inoculant, organic matter on sulfur oxidation trend and then the release of some nutrients in wheat cultivated calcareous soils. A completely randomized factorial experiment was conducted in two calcareous soils using three replications, eight levels of sulfur, two levels of organic matter, and two levels of Tthiobacillus inoculants. After applying treatments, 192 pots containing 5 kgs soil were incubated at 28 oC for 3 months. At 0,15,30,60 and 90 days after incubation soil samples were taken to analysing for pH, EC, and available phosphorus, iron and zinc. The resuls showed that in both two calcareous soils the nutrients concentration increased with increasing time, and 60 days after incubation reached to maximum level. Thiobacillus inoculation significantly increased sulfur oxidation and nutrients release compaired with uninoculated control. Organic matter application due to improvement soil physical chracteristics and increasing numbers and activities of heterotrophic sulfur oxidizing microorganis increased sulfur oxidation rates, nutrients concentration and EC, but decreased soil pH value. The sulphate concentration increased with increasing applied sulfur rates, phosphorus increased innitial, then decreased, but zinc availability changes was not significantly.