The yield and nitrogen use efficiency of Green Super Rice varieties in ratoon rice system

<p indent="0mm">Enhancing nitrogen (N) use efficiency and reducing N fertilizer input are crucial for promoting the green and efficient development of ratoon rice. Green Super Rice (GSR) is characterized by their superior ability to utilize N efficiently, enabling high productivity with lower fertilizer inputs. However, their yield, yield formation, and N utilization patterns under the ratoon rice system remain unclear. This study was conducted in Qichun, Hubei Province, during 2023 and 2024 to systematically evaluate four candidate GSR varieties and two check varieties under an N fertilizer rate of 90 kg N/ha for main season and 75 kg N/ha for ratoon season (equivalent to 50% of conventional rate). Results showed that the candidate GSR varieties (Weiliangyou8612, Longliangyou8612, Yongyou4949, and Yongyou6711) achieved annual yields of 15.7–17.2 t/ha in 2023 and 16.0–17.5 t/ha in 2024, representing yield increases of <sc>9.7%–37.8%</sc> and 15.9%–37.8% over the check varieties (Liangyou6326 and Huanghuazhan). Higher spikelet number per panicle, greater total dry matter accumulation, and higher harvest index were key agronomic traits contributing to the high yield of the candidate GSR varieties. Compared with the check varieties, total N uptake of the candidate varieties increased by 12.3% in the main season and 16.1% in the ratoon season, while their N harvest index and N use efficiency for grain production in the ratoon crop increased by 13.7% and 24.8%, respectively, indicating an enhanced N absorption and utilization under low-N conditions. In summary, the use of GSR varieties in ratoon rice production can achieve both high yield and high N use efficiency under reduced N fertilizer input, offering a promising pathway toward sustainable and resource-efficient rice cultivation.