## 4 Discussion
### Grain Yield, N Agronomic Efficiency and Water Use Efficiency under N Management Practices  
N application is an important factor affecting wheat yield, influenced by factors such as regions, varieties, and management measures. The results of previous studies on yield were different. A study showed that grain yield did not change significantly when the N application rate of winter wheat exceeded 120 kg ha\({}^{-1}\)[41]. [PERSON] et al. [42] found that the grain yield showed a trend of first increasing and then decreasing with the increase of N application. In order to obtain a yield of more than 9000 kg ha\({}^{-1}\), the recommended N rate in the NCP was 240-277 kg N ha\({}^{-1}\)[43]. However, in this study, in the high-fertility soil with a grain yield exceeding 10,500 kg ha\({}^{-1}\), grain yield increased with the increase of N application rate under the T, while under the F treatment, the grain yield of N2 was significantly higher than other treatments, indicating that fertigation could reduce N application rate and achieve high grain yield (Table 1). N application method had a significant impact on grain yield. Previous studies showed that the integration of water and fertilizer had a significant impact on 1000-grain weight but had no significant effect on grain number per spike [16; 44]. In this study, the result showed that under N2, the F increased the spike number and 1000-grain weight compared to T but had no significant effect on grain number per spike. However, there was no significant difference in grain number per spike and 1000-grain weight between N1 and N3. It can be seen that under micro sprinkling fertigation, an appropriate N application rate provided a good material basis for population construction and grain development and created favorable conditions for the formation of higher grain yield. The reasons may be that the F treatment resulted in a more uniform distribution of N in the soil compared to T, which was beneficial for the establishment of tillering in the population [45]. On the other hand, under the F, deep root length density was higher than that of T, which was conducive to the absorption of nitrate N and water [46; 47]. Increasing N uptake was beneficial for the development of photosynthetic systems, such as chloroplasts, amino acids, and enzymes, leading to more photosynthetic assimilation transport from the green organs into the grains, thereby increasing grain yield [48]. On the contrary, excess N was stored in vacuoles and did not participate in N assimilation [49].  
Therefore, high N input cannot guarantee higher grain yield and may also reduce N use efficiency, as N fertilizer input rate far exceeds crop demand [50]. In addition, due to the lack of synchronization between N demand and supply, N losses exceeded 50%, significantly decreasing N use efficiency. The nutrient absorption of crops is closely related to fertilization, irrigation, and soil conditions. An appropriate fertilization method significantly reduce N losses [51]. The integration of water and fertilizer can save 40-60% of chemical fertilizers [52]. In this study, compared with T, the F increased the NAE by 19.30% and the WUE by 3.47% (Figure 8). It could be seen that fertigation was beneficial for wheat to uptake water and N, reducing ineffective losses of soil water and N. Meanwhile, under the F, when the N application rate was 210 kg ha\({}^{-1}\) (N2), both NAE and WUE obtained were significantly higher than in other treatments. In summary, adopting fertigation method that integrated water and fertilizer, along with the N rate of 210 kg ha\({}^{-1}\), was the suitable management practice for wheat in high-fertility soil with the grain yield exceeding 10,500 kg ha\({}^{-1}\).