Optimizing nitrogen management for higher grain yield and nitrogen use efficiency in summer maize by coordinating the N supply–demand balance

Characterizing the N uptake and utilization of different maize hybrids is essential for optimizing N application and increasing the profits from maize production. Research trials were conducted with controlled-release urea (CRU) as a base fertilizer (TC) and urea split application in one (T1), two (T2), or three (T3) stages to evaluate the effects on N uptake, N use efficiency (NUE), and yield using the ¹⁵N tracer technique and two maize hybrids: DH518 (a mid-early-maturing hybrid) and DH605 (a late-maturing hybrid). According to the results, compared with urea, CRU as a base fertilizer and urea split applications in two and three stages significantly increased grain yield and NUE while reducing environmental N loss. Compared with T1, the grain yields of the TC, T2, and T3 treatments were respectively increased by 11.1, 9.8, and 11.7% in DH518 and by 16.4, 15.7, and 22.9% in DH605. Regression analysis showed that the grain yield of DH518 displayed a bilinear trend with an initial rapid increase and then a slow increase with increases in post-anthesis N accumulation, total N accumulation, N recovery efficiency, and N nutrition index (NNI). By contrast, DH605 consistently showed a linear regression relationship with a rapid increase. The crop recovery N efficiency (CRN) values in the T3 treatment for urea applied at the sowing stage and as topdressing at the 9th-leaf stage (V9) in DH518 were 60.0 and 62.4% higher than under topdressing at the tasseling stage (VT) stage, respectively, while the CRN values of urea topdressing at the V9 and VT stages in DH605 were 37.7 and 37.1% higher than when applied at the sowing stage, respectively. The higher pre-anthesis N demand and shorter growth period of DH518 maintained the N supply–demand balance, resulting in the NNI (NNI≥0.988) falling within the range of a low yield increase under the T2 and TC treatments, while the N status of DH605 plants only reached optimal levels in the T3 treatment. Therefore, a three-stage split application of urea or applying CRU as a base fertilizer and topdressing with urea in the later growth stages is recommended for obtaining an optimal yield in mid-late-maturing hybrids. In addition, for mid-early-maturing hybrids, applying CRU or reducing the number of split applications, e.g., a two-stage split application, can ensure an adequate N supply in the later growth stages and increase production, and thus profits.