Evaluation of a Hybrid Fertilizer Based on Hydroxyapatite Nanoparticles Supported on Zeolite in a Tomato Crop

In recent years, phosphorus (P) nanoparticles have emerged as promising alternatives to conventional fertilizers. This study evaluated zeolite-fixed hydroxyapatite nanoparticles (nHAP) for greenhouse tomato cultivation, comparing their efficiency with phosphate rock (positive P input) and quartz sand (negative P Carrier). Material characterization by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and zeta potential analysis revealed that zeolite was identified predominantly as clinoptilolite, phosphate rock as phosphate-bearing aluminosilicates, and quartz sand as crystalline quartz; in all cases, the materials exhibited negatively charged surfaces. Hybrid fertilizers were formed through electrostatic interactions between zeolite and nHAP, confirming the successful development of a zeolite-based carrier for nanohydroxyapatite delivery. Application of 0.01 g·Department of Agronomy, Campus de Excelencia Internacional Agroalimentario, ceiA3, Almeria University, La Canada, 04120 Almeria, SpainL−1 nHAP increased the effective quantum yield of Photosystem II by 0.64 compared to the control at midday. Fruit firmness showed no significant differences among treatments. The highest sugar and soluble solids content was observed with 0.1 g·L−1 nHAP (6.84 °Brix), whereas the 1 g·L−1 treatment enhanced pigment concentrations, reaching 5.9 mg·g−1/g chlorophyll a, 2.92 mg·g−1 chlorophyll b, and 2.82 mg·g−1 carotenoids. The 0.01 g·L−1 dose of nHAP maintained quality characteristics and marginally increased yield; however, yield decreased at higher nHAP concentrations, opening new research opportunities to optimize this nanofertilizer.