Synthesis of Elemental- and Nano-sulfur-enriched Bio-organic Phosphate Composites, and Their Impact on Nutrients Bioavailability and Maize Growth

Higher pH of calcareous soils and mineral fertilizers lowers the bioavailability of plant nutrients. Hence, it requires amending the nature of nutrients input through suitable bioactive materials, like sulfur (S), organic, microbial, and nano-materials. This study assessed the effects of S-enriched composites of organo-phosphate (OP) and bio-organic phosphate (BOP) on soil and plant attributes. Elemental sulfur (ES) and nano-sulfur (NS) were admixed separately in compost and rock phosphate (RP) with/without sulfur-oxidizing bacteria (SOB), viz., Acidithiobacillus thiooxidans . Sulfur-based amalgams were incubated at 25–35 °C for 60 days to develop S-enriched organo-phosphate (ES-OP) and bio-organic phosphate (ES-BOP and NS-BOP) composites. Greenhouse and micro-plot experiments were conducted to evaluate the impact of these composites on nutrients bioavailability and vegetative growth of maize. Treatments included control (no sulfur), ES (12.5 kg ha −1 ), ES-OP (50 kg ha −1 ), ES-BOP (50 kg ha −1 ), and NS-BOP (50 kg ha −1 ) application in soil. Inoculation with SOB in both ES-BOP and NS-BOP reduced the pH and increased macronutrients as compared to ES-OP. Thus, ES-BOP and NS-BOP improved maize growth and soil nutrients status. Composite NS-BOP rendered the highest N, P, K, and S concentrations in both soil and plants due to lower soil pH. Application of S-BOP containing Acidithiobacillus thiooxidans , and use of nano-S are beneficial for improving nutrients bioavailability and plant growth in calcareous soils via pH reduction. These composites are low-cost, nutrients-rich, and have greater efficiency than fertilizers in calcareous soil.