Encapsulation and characterization of slow-release microbial fertilizer from the composites of bentonite and alginate

• The B–NaAlg could be ideal encapsulated wall material for slow-release of bacteria.
• Bentonite and alginate prepared Rs-2 microcapsule have desired release behavior.
• Bentonite in polymers decreases the cost of encapsulated microbial fertilizer.
• The release mechanism of Rs-2 capsule was the porosity release model.

Raoultella planticola Rs-2 was innovatively encapsulated with sodium bentonite and alginate (NaAlg) composites to develop efficient slow-release biofertilizer formulations and minimize production costs. These microcapsules were spherical in shape and their encapsulation efficiency was nearly 100%. Approximately 88.9% of Rs-2 in dried microcapsules of bentonite–NaAlg survived after 6 months of storage. The NaAlg amount required to produce desirable bentonite-blended Rs-2 microcapsules was significantly lower than that of single NaAlg. Swelling, biodegradability, and release rate increased with increasing NaAlg content and decreased with increasing bentonite content. All release curves of bacteria from the bentonite–NaAlg microcapsules presented an initial burst followed by a gradual increase manner, which mainly implied the release behavior followed a first-order release model. Thus, bentonite–NaAlg composites could be ideal low-cost encapsulated wall materials for slow-release bacterial fertilizers in farmlands.