Acid sulfate soils are characterized by low soil pH, high concentrations of soluble iron and aluminum, and limited nitrogen availability, which constrain soil fertility and crop productivity. This investigation was conducted to assess how oil palm empty fruit bunch (OPEFB) biochar and poultry manure influence soil chemical behavior and nitrogen dynamics in acid sulfate soils. Experiments were arranged in a two-factor completely randomized design (CRD) with three replications. The treatments comprised OPEFB biochar application rates ( and ) and poultry manure doses ( and ). Parameters analyzed consisted of soil pH, oxidation-reduction potential (), ammonium (), and nitrate () levels. Statistical analysis revealed that the synergistic combination of OPEFB biochar and chicken manure significantly altered soil pH, , and  concentration, whereas  contents were governed exclusively by individual factor effects. Independently, both soil amendments significantly promoted  accumulation. The optimal outcome was recorded at  OPEFB biochar coupled with  poultry manure, yielding peak pH (), minimal redox potential (), alongside maximum concentrations of  () and  (). Overall, co-application of OPEFB biochar and chicken manure serves as an effective strategy to optimize soil chemical conditions and improve nitrogen availability in acid sulfate media.