Slow-Release DAP Fertilizer Coated with Bacillus velezensis FB2 and Polyvinyl Alcohol for Sustainable Maize Production

Purpose: Phosphorus is prone to fixation with ions present in the soil, forming chelates that render it relatively inaccessible to plants. The novelty of this study lies in the development of a biologically coated slow-release diammonium phosphate (DAP) fertilizer by integrating Bacillus velezensis FB2 with polyvinyl alcohol (PVA) to simultaneously regulate nutrient release and enhance phosphorus availability for maize production. Methods: Four fertilizer treatments, including uncoated DAP, Bacillus velezensis FB2–coated DAP, PVA-coated DAP (0.5%), and combined Bacillus velezensis FB2 + PVA-coated DAP were prepared using a fluidized bed spray coating system and evaluated for nutrient release, microbial survival, maize growth, nutrient uptake, and soil properties under pot conditions. Results: The PSB + PVA-coated DAP significantly reduced nutrient release compared with uncoated DAP, with phosphorus release decreasing from 42.87% to 18.98% and nitrogen release from 51.75% to 26.75% after 300 min. This treatment also resulted in the greatest improvement in maize growth performance, including plant height (158 ± 2.4 cm), shoot dry biomass (13,600 ± 1850 kg ha⁻¹), and phosphorus uptake (11.45 ± 1.5 kg ha⁻¹). Soil available phosphorus increased to 41.20 kg ha⁻¹, indicating improved nutrient availability under coated fertilizer application. Conclusion: The developed PSB and PVA-coated DAP fertilizer improved phosphorus use efficiency and maize growth by providing controlled nutrient release and enhancing phosphorus availability. This formulation can be used as a practical slow-release fertilizer option for maize production systems to reduce nutrient losses and improve fertilizer efficiency under conventional agricultural practices.