Effect of Sulfur and Thiobacillus on Soybean Growth and Uptake of Some Nutrients in Four Calcareous Soils with Different Buffering Capacities

Sulfur is the most important acidifying material which, due to having relatively low-cost, is commonly used for lowering soil pH and improving the availability of some soil nutrients in many regions of the world. The efficiency of sulfur application depends on many factors, such as the ability of calcareous soil to neutralize the acid resulting from sulfur oxidation. Therefore, determining the best rate of S-application to calcareous soils with different buffering capacity has an especial importance. With regard to sulfur utilization in order to increase nutrients availability in calcareous and alkali soils, few researches have been done about the rate of sulfur application and its relationship with soil calcium carbonate content. Hence, this investigation studied the effect of sulfur rates with Thiobacillus inoculant on soybean growth and uptake of some nutrients in 4 calcareous soils with different buffering capacity. To this end, a completely randomized factorial experiment was conducted using three replications, seven levels of sulfur applications (the rates to neutralize 0, 3.1%, 6.25%, 12.5%, 25%, 50%, and 100 percent of soil calcium carbonate content) and four different calcareous soils (soils with 8%, 14%, 22%, and 38 percent of calcium carbonate). The analysis of data by SAS software showed that application of sulfur at the rates needed to neutralize 50 percent of calcium carbonate in soils, significantly increased the uptake of nutrients. But, further application of sulfur, decreased growth parameters and nutrient uptake by plants.