Impacts of mineral and biofertilizers on rhizosphere and bulk-soil carbon, sulfur, and C/S ratio in maize for soil sustainability

Balanced carbon–sulfur (C-S) dynamics are crucial for maintaining soil fertility and sustaining crop productivity. This study examined how mineral and biofertilizers affect total sulfur (S), organic carbon (OC), and the C/S ratio in maize rhizosphere and bulk soils. A field experiment was established with six treatments: an unfertilized control, urea (250 kg N ha⁻¹), ammonium sulfate (200 kg N ha⁻¹), BioHealth biofertilizer (4–5 kg N ha⁻¹), liquid effective microorganisms (EM, 400 L ha⁻¹), and a combined fertilizer containing one-quarter of each recommended dose. Total S, OC, and C/S ratios were measured after 70 and 100 days of maize growth. Ammonium sulfate consistently produced the highest sulfur concentrations in both rhizosphere and bulk soils, with increases of more than 40% over the control at both sampling times. The combined fertilizer treatment significantly enhanced OC content in both soil compartments, with up to a 25 % increase compared with the control. Urea yielded the greatest C/S ratio (approximately 15 % higher than the control), while all treatments showed a progressive decline in C/S as sulfur availability increased, confirming an inverse S-C/S relationship. These results demonstrate that integrating bio- and mineral fertilizers improves soil C–S balance and nutrient availability, offering a practical strategy to enhance soil fertility and support sustainable maize production.