Nutrient deficiencies in calcareous soils are mostly related to high soil pH whereas sulfur supplement could facilitate nutrient element uptake by the crop plants. However, inefficient sulfur oxidation in soils is a limiting factor for this response. Mixing elemental sulfur with bentonite mineral can increase oxidation of sulfur since bentonite provides the sulfur particles with a better dispersion condition following absorption of water. Purpose of this study is to evaluate the efficiency of sulfur-bentonite granules with various proportions of bentonite to improve nutrient element uptake by the crop plants cultivated in calcareous soil. Four treatments of the sulfur-bentonite granules having 10, 20, 30 and 40 percentages of bentonite compared to the controls with no granules were applied to maize crop plants (Zea mays L.) cultivated in pots filled with an inoculated calcareous soil using Thiobacillus thioparus. At the end of the 80 days growth period; the results revealed significant soil pH decrease and growth parameters improvement with increasing bentonite proportion of the granules among the treated pots. Anyway, it appeared that a bentonite proportion of more than 30% in the granules can reverse improving trend of growth parameters in the cultivated plant. It was also confirmed that efficiency of the sulfur-bentonite granules is mostly contributed to increasing uptake of micro-nutrients of iron, manganese and copper alongside macro-nutrients of sulfur and phosphorus by the crop plants cultivated in the studied calcareous soil.
