Sulfur Oxidation under Different Moisture Conditions and its Effect on some Chemical Soil Characteristics

Sulfur is mainly used to reduce soil pH and increasing nutrients availability in the calcareous soils. However, this process strongly depends on oxidation rate and its affecting factors (e.g. soil moisture content). In this research, the impacts of two soil moisture regimes (40 and 60 % of saturation) and four Sulfur levels (0, 500, 1000 and 10000 kg ha-1) inoculated with Thiobacillus bacteria on sulfur oxidation rates and some chemical soil characteristics were assessed in a complete randomized blocks design with three replications and two soil types (Kharghani and Khaldar) during one year and under constant 25 Co temperature. In this research, soil pH, electrical conductivity (EC), Phosphorus (P), Iron (Fe), Zinc (Zn) and sulfate concentration (SO42-) were measured. The results revealed that the pH adversely significantly (P<0.01) decreased with increasing sulfur amount, while EC, Fe, Zn and SO4 increased. The highest amount of pH reduction, increasing of EC, Fe, Zn and SO42-observed with application of 10,000 kg Sulfur ha-1. Finally, the respective difference for pH, EC and SO42-compared withcontrol treatment in the Khargani soil were 0.38 units, 1.72 dS m-1, 2588 mg kg-1 and 60 days’ incubation; and in khaldar soil 2.1 units, 3.2 dS m-1and 4984 mg kg-1 in 360 days’ incubation. The amount of Fe and Zn available were found 3.53 and 0.87 mg kg-1, respectively indicating significant increasing compared with control plot in Khaldar soil. The highest P content was observed 0.5 and 4.1 mg kg-1 in Khargani and khaldar soils, respectively followed by 1000 kg Sulfur ha-1 application. It is concluded that the amount of sulur oxidation decreased followed by increasing in both sulfur content and incubation period. The highest increment was observed by applying 500 kg Sulfur ha-1. According to the results, Sulfur application up to 1000 kg ha-1 is suggested.