Biofertilizers can be a viable alternative to chemical fertilizers for providing the N required by a crop. It is important to know the N mineralization potential of bio-fertilizers to avoid deficiencies or excesses of N resulting from the addition of the product to the soil. In order to determine the N mineralization in soil amended with biofertilizers, a destructive sampling experiment was conducted. The treatments included compost, biochar, and compost + biochar with two different commercial Azotobacter sp. products. The controls included soil alone and the commercial fertilizers urea and NH₄NO_3. Each treatment, in triplicate, was applied to 1 kg of soil. The application rate and method were the same as in a parallel experiment in the field with a citrus crop on the farm at the Technical Professional High School in Los Chiles, Alajuela, Costa Rica. Seven samplings were conducted for each treatment and were analyzed for soil pH y concentrations of NH₄ ⁺-N, NO₃^--N, total C and N total. Treatments with the least amount of inorganic N were those amended with biochar or with Azotobacter sp. without other amendments. These results were statistically similar to the results of the control soil that received no amendments. The highest concentration of the inorganic N, 131 mg/kg in 16 weeks resulted from application of compost + biochar. These results were attributed to a positive interaction between compost and biochar that accelerated the decomposition process and the multiplication of microorganisms, contributing to the mineralization process. The results of the biochar + compost treatments were not statistically different from the results obtained with the application of the commercial fertilizer treatments, indicating the possibility of replacing the application of commercial fertilizers with amendments of compost + biochar.