Optimizing phosphorus released in calcareous soil amended with bone char and bone ash using response surface...

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.