The aim of this study was to assess the effects of a biochar-based slow-release P fertilizer (BBSRPF) produced from a corn stover-derived biochar (CSB), compared to mineral fertilization and co-application of CSB itself and mineral fertilization on bioavailability of soil P and spinach production, as well as, foliar macronutrients (N, P and K), protein, and ascorbic acid in plants. First, CSB was produced from corn stover. Then, P loading process was done with a KH2PO4 solution for BBSRPF production. Afterwards, a greenhouse experiment was performed for 70 days using a factorial design with the following treatments: mineral NPK fertilization (F), CSB and mineral NPK fertilization (BC) and BBSRPF and mineral NK fertilization (P-BC). After this, soil samples were collected and the plants were harvested to determine changes in soil physicochemical properties, bioavailability of soil P, leaf content of P, N, K, ascorbic acid, and protein. Besides, fresh and dry biomass, and crop yield were also determined. The P-BC treatment significantly increased bioavailable soil P by ~ 72% compared to F and BC treatments. Furthermore, P, N, K, protein, ascorbic acid content, and yield of spinach pants were significantly increased by ~ 29, 52, 33, 20, 21, and ~ 25% when P-BC treatment was applied, respectively. Incorporation of P into the biochar matrix is an effective strategy to increase spinach P use efficiency in tropical soils. Therefore, BBSRPF could totally replace conventional mineral P fertilizers without compromising crop yield, and increasing the nutritional quality of spinach plants. © 2021, Sociedad Chilena de la Ciencia del Suelo.