Problems faced in tidal swamp land include low soil pH, low nutrient content, and high levels of Aluminum and Iron. The aim of this research was to determine the effect of the combination of NPK fertilizer and Futura Coal fertilizer on the availability of Phosphorus in tidal swamp land and to determine the relationship between the solubility of Aluminum and Iron on the availability of Phosphorus in tidal swamp land. This research was carried out at the Chemistry Laboratory, Soil Department, Faculty of Agriculture, Lambung Mangkurat University from October 2023 to December 2023 using a single factor Randomized Block Design with 5 treatments and 3 replications of each treatment to obtain 15 experiments. The application of a combination of NPK fertilizer and Futura Coal fertilizer can increase the availability of phosphorus, organic C and soil pH and can reduce the solubility of aluminum and iron in tidal swamp land. Apart from that, no relationship was found between the solubility of Aluminum and Iron on the availability of Phosphorus, but a relationship was found between Aluminum and soil pH with a correlation coefficient of -0.75, between C-organic and Aluminum with a correlation coefficient of -0.59, between C-organic and Soil pH with a correlation coefficient of 0.95, between organic C and soluble iron with a correlation coefficient of -0.85, between soluble iron and soil pH with a correlation coefficient of -0.92. Next, an equation is obtained that represents this relationship.