Elemental sulfur and Thiobacillus culture alter nutrient availability and maize growth in compost-amended calcareous soil

Elemental sulfur can improve nutrient availability in calcareous soils, but its effectiveness depends on oxidation conditions, soil buffering, and associated organic and microbial amendments. A controlled greenhouse experiment evaluated seven elemental sulfur rates (0, 250, 500, 750, 1000, 1250, and 1500 kg ha⁻¹) combined with either sterile water or a live Thiobacillus thioparus culture treatment in a compost-amended calcareous clay soil. Each of the 14 treatment combinations had three replicate pots. All pots received mature composted cattle manure at 20 Mg ha⁻¹ on a dry-matter basis, and one hybrid maize plant was grown per pot for 86 days. Increasing sulfur rate lowered post-harvest soil pH and increased available P, S, Fe, Cu, Zn, Mn, and B. The lowest pH (6.68), highest available P (12.8 mg kg⁻¹), and highest available S (205 mg kg⁻¹) occurred at 1500 kg S ha⁻¹ with the culture treatment. Post-harvest total N declined as shoot N removal increased, whereas available K changed little. Total aboveground dry biomass increased from 466–478 g pot⁻¹ at 0 kg S ha⁻¹ to 744–812 g pot⁻¹ at 1500 kg S ha⁻¹. Uptake of all measured macro- and micronutrients followed a similar increasing pattern. The greatest responses within the tested range occurred at 1500 kg S ha⁻¹, particularly in culture-treated pots. These results show that micronized elemental sulfur, under adequate moisture and warm greenhouse conditions, can substantially alter nutrient availability and maize performance in compost-amended calcareous soil. The highest tested rate should not be interpreted as a field optimum without multi-soil and field validation.