Redox cycling of sulfur via microbes in soil boosts the bioavailability of nutrients to Brassica napus

Abstract

Deficiency of sulfur (S) has been recognized for both dry and wetland plants as a significant growth limiting factor. S-oxidizers enhance the oxidation rate of S and increase sulfate (SO4 − 2) production by making them available in critical growth stages, resulting in higher plant growth and yield. A two-phase study was undertaken to assess the effectiveness of microbial redox reactions on soil nutrient bioavailability and crop growth. In the first phase isolation of S bacteria was carried out while in the second phase, a pot experiment was conducted and these bacteria were evaluated as a nutrient source along with different ratios of NPK fertilizer by growing canola (Brassica napus) as a test crop. Treatment combinations were, viz., Control (no inoculum), ½ NPK fertilizer (50, 30, and 25 kg ha−1), Full NPK fertilizer (100, 60, and 50 kg ha−1), ½ NPK+SOB, ½  NPK+SRB and ½ NPK+SOB+SRB. Sulfur oxidizing bacteria (SOB) strains were isolated from samples and then screened based on pH reduction (in thiosulphate broth). Sulfur-reducing bacteria (SRB) are characterized by their anaerobic energy metabolism based on the dissimilatory reduction of SO4−2 to hydrogen sulfide (H2S) or S ° to be useful for SOB. Among different bacterial consortiums, the best results for nutrient bioavailability (macro- and micronutrient) in soil and plant the treatment ½ NPK+SOB+SRB compared to full NPK increased soil N, P, K, and SO₄ by 15.9%, 38%, 2.0%, and 72%, respectively. In plants, it boosted N, K, and SO₄ by 7.7%, 31%, and 239%, respectively. The greatest pH reduction (4%) was observed with ½ NPK+SOB relative to full NPK. This study demonstrates that microbial inoculation along with ½ NPK increases the bioavailability of macro- and micronutrients for crops.