Organic materials, such as biochar and organic compost, can reduce P sorption mechanisms and improve soil fertility, benefiting the reclamation of areas impacted by mining. This study evaluated how the chemical properties of Fe mining soil, the adsorption of P onto this substrate, and the growth of the native plant Dioclea apurensis, were affected by the application of açaí biochar (BC), organic compost (OC), and different P doses. Substrate collected from mining soil piles was incubated for 30 days with BC or OC. Each mining substrate with or without the addition of BC or OC received five doses of P (0, 40, 80, 120, and 240 mg∙kg−1 P). The addition of BC or OC promoted an increase in pH and nutrient availability (P, K, Ca, and B) in Fe mining soil. However, plants grown in the unamended mining soil (W) showed higher growth. The maximum P adsorption capacity decreased as a function of the addition of BC. We conclude that the application of BC reduced P sorption, while the application of either OC or BC altered the chemical properties of the soil and caused contrasting effects on P dynamics in Fe mining soil, and these treatments also affected plant growth.