Aims <p>Soil nitrogen supply capacity is primarily governed by organic nitrogen mineralization. Over 95% of nitrogen must be mineralized before plant uptake. Organic nitrogen mineralization potential (N₀) is a critical indicator to quantify mineralization. However, previous studies have determined N₀ in specific regions through lab incubation. For China's farmland, nationwide evaluation on N₀ and its controlling factors remians limited. A nationwide assessment is imperative for elucidating soil nitrogen capacity in China.</p> Methods <p>In this study, we collected 946 observations data from agricultural ecosystems across China to explore the characteristics and the main controlling factors of soil nitrogen supply indicators in farmland. Additionally, we utilized 197 paired treatment groups to investigate the extent to which different types of fertilizers could enhance the soil nitrogen supply capacity.</p> Results <p>The findings revealed that the average N₀ concentration in China's farmland soil was 105.8&#xa0;mg·kg⁻¹, with paddy soils exhibiting a 29.2% higher N₀ level compared to that of upland soils. Soil total nitrogen (STN) was the main factor controlling the soil nitrogen supply capacity. The combined application of organic and inorganic fertilizers was found to be the most effective in enhancing N₀ in farmland soils. In contrast, straw or inorganic fertilizer alone exerted a limited effect on increasing N₀.</p> Conclusions <p>This study provides a comprehensive evaluation and in-depth discussion of the nitrogen supply capacity of China's farmland soil and its main controlling factors, offering a crucial theoretical foundation for the development of a nationwide nitrogen transformation model and the optimization of farmland soil nutrient management practices.</p> Graphical Abstract <p></p>