In this study, a completely randomized design with 9 treatments at three replications was used to investigate the effect of Leonardite on the chemical behavior of phosphorus in a calcareous soil. The experimental treatments included a control group, three levels of phosphorus (100 and 200 mg/kg) supplied as monopotassium phosphate, Leonardite at four levels (0, 1, 3, and 5% w/w), and their combinations (P100L0, P100L1, P100L3, P100L5, P200L0, P200L1, P200L3, and P200L5). The phosphorus treatments were added to one kilogram of soil and maintained under controlled conditions for one month. Subsequently, the Leonardite treatments were applied to the soils, and incubation continued for 90 days. At the end of the incubation period, samples were taken from each treatment, and the amount of released phosphorus was measured at 2, 4, 8, 24, 48, 96, and 120 hours. The results of the kinetic investigations indicated that the addition of different levels of Leonardite increased the phosphorus (P) availability in the soil, which was attributed to the low pH and acidic functional groups present in Leonardite. The Elovich equation, with the highest coefficient of determination and the lowest standard error, was the best equation describing the kinetics of P release in the soil. This study confirmed that Leonardite application serves as an effective organic amendment in calcareous soils, significantly enhancing phosphorus availability while improving phosphorus uptake and utilization in plants. These findings demonstrated Leonardite's potential for advancing sustainable agriculture and supporting environmental conservation in arid and semi-arid regions.