## 4 Discussion
### Dry Matter Accumulation, Remobilization and Grain Filling under N Management Practices  
Dry matter accumulation is an important factor affecting the formation of grain yield. Within a certain range, as the accumulation of dry matter increases, the grain yield may increase. Therefore, improving dry matter accumulation through reasonable agronomic measures is an important way to achieve high yield. In this study, N application methods and N rates had a significant impact on the total dry matter accumulation, especially in mature stem, leaf, and grain organs (Figure 6). [PERSON] et al. [35] found that under fertigation, the photosynthetic rate of wheat leaves at anthesis and mid grain filling stages were significantly correlated with dry matter accumulation. In this study, the F treatment increased the dry matter accumulation compared to that of T. At the same time, the Pn of flag leaves significantly increased at 14 and 21 d after anthesis, indicating a significant positive correlation between them. [PERSON] et al. [36] found that the accumulation of dry matter in wheat increased with the increase of N rate. This was similar to the results of T treatment in the study. However, under the F, with the increase of N application rate, the accumulation of dry matter did not further increase, and there was no significant difference when the N rates were 210 kg ha\({}^{-1}\) (N2) and 270 kg ha\({}^{-1}\) (N3). It could be seen that a certain threshold for the accumulation of dry matter existed, which increased with the increase of N application rate within a certain range. Further enhancing the N application rate did not increase the accumulation of dry matter. At the same time, when the N rate was 210 kg ha\({}^{-1}\) (N2) under the F, the dry matter assimilation after anthesis was significantly higher than other treatments, and its contribution to grain was also increased (Table 2).  
Grain filling is the final stage of fertilized ovaries developing into cryopses and is significantly influenced by pre-anthesis remobilization of dry matter and post-anthesis photosynthetic complex synthesis, both of which determine the final grain weight [37]. The grain filling rate and effective filling duration affect the sink strength of grain [38]. In this study, only under N2, the duration and active filling period of F were significantly higher than those of T (Table 3). This indicates that an appropriate N rate under fertigationincreases the effective duration of grain filling, thereby increasing grain weight. The results of 1000-grain weight also indicated it. Under the two N application methods, as the N rate increased, the Tmax, T, and D all showed a gradually increasing trend. These results might be related to senescence characteristics, as delaying premature leaf senescence is beneficial for prolonging effective grain filling period [39]. [PERSON] et al. [40] reported that with the increase of N application rate, the Vmax first increased and then slightly decreased. It was similar to the results of the N application treatment in 2022-2023 wheat season. However, the Vmax showed a decreasing trend with N rate in 2023-2024. The difference in results between the two the seasons might be related to precipitation at filling stage.