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【Objective】The present paper aimed to explore the feasibility of reducing the amount of nitrogen fertilizer and a reasonable nitrogen reduction model under late sowing wheat in the Jianghan Plain. 【Method】 Field experiments were conducted with Zhengmai 9023 under traditional and late sowing date with three nitrogen treatments differing in ratios of basal to topdressing. The changes in wheat yield and its constituent factors and nitrogen related indicators were compared across treatments. 【Result】（i） Under the same nitrogen application rate and base-topdressing ratio, grain yield, panicle number and 1000-grain weight were significantly reduced delayed the sowing date. Reduced total dry matter accumulation during flowering and maturity under late sowing was due to the decrease in dry matter accumulation in leaves and stem sheaths; The dry matter accumulation in spike did not show significant change. The changes in dry matter accumulation at maturity were related to leaves, stem+sheaths and grain husk+spike axis. Under the same nitrogen application rate and base-topdressing ratio, the nitrogen accumulation in wheat at flowering and maturity decreased as well; Nitrogen accumulation in flowering leaves of increased under late sowing, but nitrogen accumulation in stem+leaf sheath, ripe leaves and ripe grain husk+spike axis decreased. Under the same nitrogen application rate and base-topdressing ratio, the spike formation rate and nitrogen use efficiency were significantly reduced under late sowing.（ii）Under different nitrogen fertilization treatments and the same sowing date, nitrogen fertilization can be reduced from 180 to 150 kg/hm² under late sowing with insignificant change in yield decreased by 3.33 kg/hm²（M1） and 293.34 kg/hm²（M2） in 2019—2020; 158.67 kg/hm²（M1） and 13.50 kg/hm²（M2） in 2020—2021. The reduction was much lower than that of normal sowing, and the reason was that the number of spikes and grain number per spike were stable when the nitrogen application rate was reduced from 180 to 150 kg/hm², and the 1000-grain weight increased to some extent. Further reducing the amount of nitrogen applied, the yield change under the two sowing dates did not reach a significant level. Under the same base-topdressing ratio, reducing nitrogen application rate, the nitrogen accumulation in the stem+leaf sheath and spike at the flowering stage and grain husk+spike axis were significantly reduced, but dry matter accumulation did not change significantly. Under the same sowing date and base-topdressing ratio, reducing nitrogen application rate, spike formation rate increased significantly, M1 nitrogen utilization efficiency increased significantly, and M2 nitrogen utilization efficiency remained stable. 【Conclusion】Under the conditions of continuous optimization of nitrogen fertilizer management mode, the yield of late sowing wheat under nitrogen reduction treatment was not significantly reduced compared with normal nitrogen yield, but the spike formation rate and nitrogen use efficiency were significantly improved. After a delay of 20 days, the recommended nitrogen fertilizer management model is that the ratio of base to topdressing is m（base fertilizer）∶ m（top dressing before winter）∶ m（top dressing at jointing stage）=1∶1∶1, and the nitrogen application rate can be reduced from the normal nitrogen application rate to 150 kg/hm². [ABSTRACT FROM AUTHOR]

[Objective] This paper studies the optimal rice nitrogen fertilizer management measures under the condition of returning the whole wheat straw to the field, in order to provide a theoretical basis for the utilization of straw returning to the field and the reduction of high-efficiency nitrogen application. [Method] The soil culture experiment was adopted, and the nitrogen application rate was set as constant nitrogen application (A1, 270 kg/hm²) and reduced nitrogen application (A2, 240 kg/hm²). Nitrogen management was used to set a high-ratio basal nitrogen fertilizer (B1, basal fertilizer: tiller Fertilizer: ear fertilizer = 5: 2: 3) and high-ratio tiller nitrogen fertilizer (B2, base fertilizer: tiller fertilizer: ear fertilizer = 2: 5: 3), with no nitrogen (CK, 0 kg/hm²) as the control, The characteristics of plant height, dry matter accumulation and distribution of different nitrogen levels and nitrogen management in key growth stages of rice were systematically compared. [Result] Under the condition of returning all wheat straw to the field, the plant height of rice in the late stage of the reduced nitrogen application was significantly lower than that of the constant nitrogen application, and the plant height increased under the two nitrogen application rates to increase the ratio of tiller nitrogen fertilizer (2∶5∶3). high. From booting stage to maturity stage, the dry matter quality of the aboveground rice in the treatment of reduced nitrogen application was lower than that of the treatment of constant nitrogen application. From the heading stage to the maturity stage, the rice leaf biomass and its proportion to the total biomass of the reduced nitrogen application were lower than that of the constant nitrogen application, and the proportion of the leaves under the high-ratio tiller nitrogen fertilizer treatment under the two nitrogen application rates was higher; The stalk biomass of the reduced nitrogen fertilization treatment was lower than that of the constant nitrogen fertilization, and the ratio of the tiller nitrogen fertilizer ratio was increased under the two nitrogen fertilization rates. The stalk biomass proportion of the stalk biomass was reduced; the reduced nitrogen fertilization treatment had a constant leaf sheath biomass and distribution Nitrogen application decreased, and the difference in leaf sheath biomass at heading stage reached a significant level; ear biomass and its proportion were higher than that of constant nitrogen application under reduced nitrogen application, and the ratio of tiller nitrogen fertilizer increased under reduced nitrogen application. The amount is reduced. [Conclusion] It can be seen from the above that under the condition of fully returning wheat straw to the field, high plant height and above-ground dry matter quality can be obtained in the middle and late stages of rice under constant nitrogen application, and the biomass and distribution ratio of leaves, stems and leaf sheaths are generally increased. Under constant nitrogen application, increasing the ratio of tiller nitrogen fertilizer is beneficial to the material production and accumulation of rice vegetative organs, while reduced nitrogen application is beneficial to the material accumulation and distribution of rice panicles. [ABSTRACT FROM AUTHOR]