A Novel Hybrid Smart Fertilizer of Biochar and Nano-Hydroxyapatite: Characterization and Performance for Improving Sandy Soil Fertility

Sandy calcareous soils in arid regions suffer from low phosphorus (P) availability due to high fixation rates, limiting crop productivity. This study investigates a novel hybrid smart fertilizer (BN) composed of olive pomace biochar (BC) and nano-hydroxyapatite (nHAP). BN was synthesized and characterized using XRD, FTIR, SEM/TEM, and zeta potential analysis. Its P release kinetics were modeled, and its agronomic performance was assessed on faba bean (Vicia faba L.) in a pot experiment under sandy soil conditions with and without wood vinegar (WV). The 1:1 BC:nHAP formulation showed a two-stage release profile: a rapid initial burst (Higuchi model, R2 = 0.86) followed by sustained zero-order release (R2 = 0.80). In the pot experiment, BN combined with WV significantly increased plant height by 36%, shoot fresh weight by 232%, and available soil P by 39% compared to conventional SSP (p < 0.05). This synergistic treatment also improved root nodulation and nutrient (N, P, K) uptake. The BC-nHAP hybrid coupled with WV acts as an efficient P delivery system, improving soil fertility in arid environments based on circular economy principles, aligning with SDGs 2, 12, and 15.