Optimizing phosphorus released in calcareous soil amended with bone char and bone ash using response surface methodology and desirability function

This study evaluated the optimization of phosphorus (P) released in calcareous soil-amended with bone ash (BA) and bone char (BC) compared to phosphate rock (PR) and single superphosphate (SSP) using a central composite design and desirability function. Incubation experiment was conducted (≃30 °C) to investigate the effects of P-levels (PL, 1000-4000 mg P/kg soil) and incubation time (14-90 days) on available-P, soluble-P, -Ca²⁺, -Mg²⁺, and soil-pH. Wetting and drying cycles were applied using distilled water (DW) and acidified water (AW). Results revealed a significant increase in soil phosphorus availability and solubility over time, particularly at higher PL. AW was more effective than DW in increasing available-P and soluble-P, -Ca²⁺, and -Mg²⁺, while reducing soil-pH and incubation time. Regardless of SSP behavior due to its high solubility, maximum amounts of available-P in BA-, BC-, and PR-amended soil for DW application were 40.92, 31.53, and 16.74 mg/kg at 40.6, 55.8, and 14 days, respectively, with PL of 3850 mg/kg for BA and 4000 mg/kg for BC and PR. For soluble-P, maximum amounts were 3.1, 2.62, and 0.85 mg/kg with AW application after incubation times of 36.8, 63.4, and 90 days, respectively, which were higher than DW application. BA-amended soil with DW and AW applications exhibited optimal responses for available and soluble phosphorus, higher than BC-amendment. PL and incubation time interactions were pronounced in enhancing the studied parameters. The study concluded that AW, simulating rhizosphere acidification, significantly optimized P-release and related parameters compared to DW. This perspective requires further research for broader applications, especially for its applications in large-scale agricultural systems. Generally, BA and BC redistributed the phosphorus solubility and availability in soil, subsequently enhancing soil fertility and sustainability as an eco-friendly phosphate fertilizer.