Background Enriching biochar with nitrogen and using it as a slow-release nitrogen fertilizer is a promising strategy to avoid excessive use of chemical nitrogen fertilizers. Therefore, this study investigated the effect of different types of nitrogen-enriched biochar on the soil’s chemical properties, nitrogen use efficiency (NUE), and growth of spinach in calcareous sandy soil. This pot experiment included 9 treatments: control (unamended soil, CK), willow branches biochar (WB), apple of Sodom biochar (ASB), marvel grass biochar (MB), halfa grass biochar (HB), nitrogen-enriched willow branches biochar (NEWB), nitrogen-enriched apple of Sodom (NEASB), nitrogen-enriched marvel grass biochar (NEMB), nitrogen-enriched halfa grass biochar (NEHB). Nitrogen-enriched biochar and biochar were added at a level of 5 g kg−1 soil. This experiment was conducted on the spinach plant. Results Soil available nitrate increased significantly with adding NEHB, NEMB, NEWB, and NEASB compared to the control treatment. Adding HB, NEHB, NEMB, NEWB, and NEASB to the soil significantly improved the fresh and dry shoot of the spinach plant compared to the control. Applying HB, NEHB, NEMB, NEWB, and NEASB treatments increased the fresh shoot of the spinach plant over the control by ~62%, 245%, 237%, 275%, and 196%, respectively. On the other hand, adding MB, WB, and ASB treatments decreased the fresh shoot of the spinach plant relative to the control by ~14%, 3%, and 14%, respectively. Applying different types of nitrogen-enriched biochar significantly improved the NUE of spinach plant compared to the original biochar treatments. Conclusions Our results suggest that nitrogen-enriched biochar can be a promising strategy in sustainable agriculture to increase soil nutrient availability, improve spinach growth, and enhance nitrogen use efficiency in spinach. Nitrogen-enriched biochar can serve as an effective and cost-efficient alternative to chemical nitrogen fertilizers.