Lemon Peel Waste as a Natural Enhancer for Increasing Phosphorus Solubilization in Phosphate Rocks

The phosphate fertilizer industry faces several challenges, including an increase in food demand, declining quality of phosphate rock (PR), and environmental concerns. Composting PR with agricultural residues, such as lemon peel (LP), presents a sustainable solution to enhance phosphorus (P) availability while mitigating environmental impacts. This study evaluated the role of LP in solubilizing P from PR through a kinetic experiment, and examined its effects on soil-available P forms via an incubation experiment. The kinetic experiment tested two commercial types of PR (Bifox: Bi-PR and Bayovar: Ba-PR) with LP doses of 0.5, 1, and 2 g. PRs were analyzed using SEM-EDS, XRD, and FT-IR techniques. The incubation experiment included PR doses of 50, 100, and 200 kg ha⁻¹, with LP doses of 1 and 2 g kg⁻¹ soil, focusing on P Olsen concentration and different P fractions. The highest LP dose (2 g LP) achieved maximum P solubilization, exceeding 30,000 mg P kg⁻¹ in Ba-PR. The release kinetics fit the Elovich model well (r² ≥ 0.962). Organic acids, such as oxalic and citric acids, have been identified as key contributors to P solubilization. SEM, XRD, and FT-IR analyses demonstrated reduced crystallinity in the PR after treatment with LP. In the incubation study, the application of PR significantly increased P Olsen concentrations and the labile NaHCO₃-Pi fraction by 20%. Furthermore, LP enhanced the less labile HCl-Pi fraction by 31%. LP significantly enhanced P release from PR, stabilized soil pH, and improved P availability. This biological approach is economical, energy-efficient, and environmentally friendly alternatives to conventional chemical methods for producing P fertilizers.