Carbon stock, physical attributes, and humic substances of soil with biofertilizer application in the Cerrado-Pantanal ecotone region

Adopting conservation practices is crucial for improving soil quality. Additionally, biological fertilizers enhance microbial activity and soil health. This study aimed to evaluate soil physical attributes, quantify total organic carbon (TOC) content, and determine the carbon content of humic substances in different management systems under biofertilizer application. The research was conducted at Mato Grosso do Sul State University, Aquidauana, Mato Grosso do Sul, with dystrophic Red Argisol (Argissolo Vermelho distrófico) soil. Three management systems were evaluated over 12 months—permanent pasture (PP), direct sowing (DS), and no-till system (NTS)—with and without biofertilizer application. The experimental design was a completely randomized 3 by 2 factorial scheme. After 12 months, disturbed and undisturbed soil samples were collected from 0 to 0.05, 0.05 to 0.10, 0.10 to 0.20, and 0.20 to 0.40 m soil layers to analyze macroporosity (Ma), microporosity (Mi), total porosity (Tp), resistance to penetration (Rp), soil density (Sd), geometric mean diameter (GMD), weighted mean diameter (WMD), and carbon contents and stocks (TOC and ΔStockC). The chemical fractionation of soil organic matter was also performed to determine carbon stocks of fulvic acid (C-FA), humic acid (C-HA), and humin (C-HUM) fractions. The PP system showed higher Mi and Tp compared to DS and NTS, but this interaction was not statistically significant. Biofertilizer application had no effect on these parameters. Regarding TOC and ΔStockC, a significant increase was observed in PP with biofertilizer at 0.20 to 0.40 m, while no effects were detected in the other systems. The C-HUM fraction predominated over C-HA and C-FA. An interaction was observed, where PP without biofertilizer had lower StockC-HA than NTS and DS without biofertilizer and PP with biofertilizer. The HA/FA ratio was above 1.0 in all treatments, and in PP with biofertilizer, the AE/HUM ratio was below 1. Overall, 12 months after the first application, biofertilizer did not influence soil physical attributes. The effect on TOC was observed only at 0.20 to 0.40 m in PP, while no significant effects were detected in the NTS and DS systems.