<p>The adverse environmental consequences of inorganic nitrogen (N) loss from fertilized soils remain a global issue. The oxidation of biochar may improve its capacity for retaining N in soils; nevertheless, the rate-dependent N retention capacity of oxidized biochar derived from different feedstocks and their impact on the associated microbial enzymatic regulators remains uncertain in fertilized soils. Using the ¹⁵N tracer technique, oxidized biochar derived from poultry manure, rice straw, and tobacco stem was comparatively assessed with raw biochar from the same feedstock on inorganic N dynamics and N recovery in fertilized soil. Results revealed that oxidation enhanced the intensity of organic functional groups, cation exchange capacity (CEC), and surface properties for all biochar types, leading to an increase in NH₄⁺ sorption and a decrease in NO₃⁻ concentration in oxidized biochar-treated soil. This modification resulted in an overall gain in the retention of N by 3%, 28%, and 27% in the treatments with oxidized biochar applied at 1% (w/w) for oxidized poultry manure biochar (OPBB), oxidized rice straw biochar (ORBB) and oxidized tobacco straw biochar (OTBB). Consequently, an increase in fertilizer N recovery rate of 13%, 46%, and 82% was recorded in OPBB, ORBB, and OTBB treatments compared to their raw biochar. Furthermore, plant-derived oxidized biochar increased N retention more than manure-derived biochar. In addition, the oxidized biochar treatments reduced soil urease activity, which was connected to a decrease in the quantity of NH₄⁺ and increased the resident time of fertilizer N in the soil. This study demonstrates that, unlike raw biochars, oxidized biochars hold great potential for reducing inorganic nitrogen dynamics, which could reduce N loss from fertilized soils alongside increasing N resident time in the soil.</p>