Potential carriers for biofertilizers: microstructural and entrapment properties

Abstract

Abstract The suitability of carrier materials for the entrapment of bacteria is an important factor in developing biofertilizers as it determines their functional properties during use and storage. This study examines the microscopic structure and entrapment properties of several potential carriers for biofertilizers. The carriers studied included rice straw, sago dregs, cassava dregs, gum, carrageenan, pea fiber, and carboxymethyl cellulose (CMC), all in powder form. The entrapment process was carried out by mixing the bacterial solution (10%) of Rhizobium, Azotobacter, Bacillus, and Methylobacterium with the carrier material by spraying and shaking followed by air drying. CMC and carrageenan exhibited a swollen structure when mixed with a bacterial solution, forming lumps. Gum, pea fiber, sago dregs, and cassava dregs swelled slightly, while rice straw demonstrated a non-swollen fibrous structure. The incorporated bacteria appeared entrapped inside the lumps and/or adhered to the surface of the lumps or fibrous particles. The largest number of bacteria was found in gum (log10 6 – log10 7) and pea fiber (log10 4 to – log10 7), followed by cassava dregs (log10 2 – log10 7), CMC (log10 2 – log10 6), sago dregs (log10 5) and rice straw (log10 3 – log10 4), while no bacteria was observed in carrageenan. Most bacteria survived in the carrier with swelling properties and loose structures. In conclusion, the microstructure of carrier materials provides information that can describe bacterial entrapment properties. This study gives important insight useful in formulating carrier materials for developing biofertilizers.