| Summary: | Supplying adequate nitrogen (N) to meet crop demand is critical for enhancing agricultural sustainability. Not only fertilizer N, but also N from other available sources should be considered in N supply capacity. We conducted a 10-year farming experiment using a split-plot design with two different main fertilizer management approaches and three N application strategies as add-on sub-treatments. Based on the experiment, we estimated the total N supply (TN<sub>supply</sub>) for the summer maize cropping system, through considering environmental, soil, crop residue, and fertilizer N sources. An appropriate TN<sub>supply</sub> was established by correlating TN<sub>supply</sub> with the relative yield (RY), N input and output, and N use efficiency (NUE). The results revealed a wide variation in TN<sub>supply</sub> (from 88 to 755 kg ha<sup>−1</sup>). The RY, N input, and N output fitted well to TN<sub>supply</sub> using linear-plateau, linear, and linear-plateau models, respectively. The lower limits of TN<sub>supply</sub> for achieving the maximum RY and N output were 361 and 358 kg ha<sup>−1</sup>, respectively. The relationship between N input and N output was described as linear-plateau. We determined the slope of the linear curve (55.4%) as the lower limit of NUE, beyond which the upper limit of TN<sub>supply</sub> was determined to be less than 497 kg ha<sup>−1</sup>. Thus, appropriate TN<sub>supply</sub> values ranged from 325 to 497 kg ha<sup>−1</sup> for summer maize production, which could ensure enough N supply for higher yields and avoid excessive N input for higher NUE and lower environmental N loss. Our findings highlight that TN<sub>supply</sub> can be an alternative indicator for evaluating N management.
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