Effects of sulfur and Thiobacillus bacteria application on some nutrients availability in soils with different buffering capacities

Despite occurrence of Plenty of nutrients, such as phosphorus and micronutrients in calcareous soils, their available form will became less than plant requirements for optimum growth. Thus deficiency of nutrient elements is a limiting factor for plant growth. The efficiency of sulfur application  in calcareous soils depends upon factors namly; soil buffering capacity and neutralizing acid coming from sulfur oxidation. Thus determination optimum sulfur application rates in calcareous  soils with different buffering capacities is an especial issue. In this study the effects of sulfur and Thiobacillus bacteria on the availability of some nutrients in 4 calcareous soils with different buffering capacity was evaluated. Factors were: sulfur application rates (the amounts of  sulfur which potentially neutralize 0, 3.1, 6.25, 12.5, 25, 50 and 100 percent of soil buffering capacity) and soil type (soils with 8, 14, 22 and 38 % of calcium carbonate equivalent). The results indicated that effects of sulfur, soil type and also their interactive effects on available P, Fe, Zn, Cu, Mn and SO₄ ^2- were significant (P<%1). In each 4 soils increasing inoculated sulfur rates, increased  available nutrients compared with control. As phosphorus, iron, zinc, manganese, copper and sulfate in control treatment were, 11.4, 2.4, 2.8, 4.2, 1.4 and 48.5 mg per kg, respectively, while they increased to 25.4, 13.1, 3.5, 28.7, 1.8 and 207.2 mg per kg in S6T1 treatment (the rate of sulfur that can neutralize 100% calcium carbonat equivalent). The soil sulphate increase in four tested soils ranged from 140 to 180 mg per kg. The most increase in micronutrients avalability in C1 soil (with 8% calcium carbonate equivalent), while the highest increase of phosphorus avalability in C3 soil (with 22% calcium carbonate equivalent), were observed.