Effects of Biological Oxidation of Sulfur on Soil Properties and Nutrient Availability in Some Soils of Iran

There are problems in solubility and bioavailability of nutrient elements in soils of Iran because of parent materials and climate. Sulfur oxidation and sulfuric acid production is one of the strategies for overcoming this problem. Many soil microorganisms including Thiobacillus are capable of oxidizing sulfur and thereby decreasing soil pH. In the present study, the effect of sulfur and Thiobacillus was studied for evaluation of some chemical soil characteristics in a factorial randomized complete block design in research fields of provinces of Khorasan Razavi, Fars, Kermanshah, Khuzestan, Qazvin and Kerman (Kerman and Jiroft). The factors including sulfur at levels of 500, 1000, and 2000 kg.ha-1, Thiobacillus at levels of 10, 20, and 40 kg.ha-1 and triple super phosphate fertilizer based on soil testing and 65% of this recommended rate. The experiment was performed both with and without plant. The results showed that the available phosphorous in soil increased significantly in many regions. The amount of sulfur exceeding 2000 kg caused increase in EC in some regions, therefore, we do not recommended sulfur application over 2000 kg.ha-1. The best treatment for this research was application of 500 to 1000 kg sulfur with combination of 10 to 20 kg Thiobacillus and triple super phosphate.According to the results of this study, application of 2000 kg.ha-1 or more sulfur is not recommended, since compared with 1000 kg.ha-1 , it does not only cause soil pH reduction and increase the availability of the elements, but also increases the electrical conductivity.