Chemical and structural characterization of post-milling biochar and its application as a bacterial carrier

Biochar is a carbon-rich material with the potential to improve soil quality, and milling can increase its surface area, potentially enhancing its suitability as a carrier for bacteria. This study aimed to produce and characterize biochars obtained from coffee pulp and chicken manure, as well as to evaluate the effect of milling on their properties and performance as carriers of the phosphate-solubilizing strain UFPI B5-8A (Pseudomonas anuradhapurensis) in maize cultivation under greenhouse conditions. The biomasses were collected, and the resulting biochars were ground for 10 hours in a ball mill. Ground and unground samples were analyzed for total carbon content, specific surface area (BET-N₂), pore volume and total pore diameter, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The biochars were also evaluated as carriers of the UFPI B5-8A strain in maize grown in soil fertilized with rock phosphate, with plant growth and soil-available phosphorus assessed. Milling did not alter carbon contents and had no effect on increasing the surface area or the number of mesopores of the biochars. The functional groups and crystalline phases of the biochars also did not change after ball milling. No effect of bacterial inoculation on maize growth was observed. Future studies should clarify how biochar characteristics, such as lignin and cellulose contents, salinity, pH, and milling time, influence bacterial survival and how the application of this biochar may affect soil biological properties