Nitrogen (N) management is an important strategy for improving the yield, grain quality, and N use efficiency of rice (Oryza sativa). Exploring appropriate N application rates is essential for high-quality rice production in China, especially in the context of the large extension of these varieties in recent years. Field experiments were conducted to study changes of grain N content and their correlations to yield and yield components using twenty high-quality rice varieties grown at three N application rates (105, 165 and 225 kg ha⁻¹) in 2019 and 2020. Additionally, a micro-plot experiment based on ¹⁵N isotope tracing technique was also conducted with two contrasting high-quality rice varieties of Y-liangyou 911 and Yeiangyoulisi under two N application rates (165 and 225 kg ha⁻¹) in 2021, with grain N accumulation, its subdivision, and N utilization investigated. We found that the grain N content of high-quality rice increased with the increase of N application rates, while there was no consistent response in grain yield. There was a significant quadratic relationship between grain yield and grain N content, while panicles m⁻² and grain-setting rate had a positive and a negative correlation with grain N content, respectively, in both 2019 and 2020. Across three N application rates and two years, the coefficient of variation (CV) of grain N content ranged from 10.36% to 21.26% among twenty varieties, of which Y-liangyou 911 had the smallest CV, and six varieties, including Yexiangyoulisi, had the largest CV. The micro-plot experiment showed that, in comparison with N₁₆₅, the grain N content, grain N accumulation, and N recovery rate increased under N₂₂₅ in both varieties, but a significant increase in grain yield was only observed for Y-liangyou 911. Grain N accumulation derived from panicle N fertilizer and its ratios to total grain N accumulation and the N recovery rate was significantly higher than those derived from basal and tillering N fertilizers. Nevertheless, increasing N application rates had much greater effects on the grain N accumulation derived from basal and tillering fertilizers and on ratios to total grain N accumulation in Yexiangyoulisi than those in Y-liangyou 911. Our results suggested that adopting a moderate N application rate (165 kg ha⁻¹) is conducive to maintaining an appropriate grain N content and achieving higher grain yield and N use efficiency as well as better quality of high-quality rice. Besides, moderately reducing basal and/or tillering N fertilizers is necessary for those varieties with a larger CV of grain N content.

Early-season rice in the middle and lower reaches of the Yangtze River is vital for China’s food security, but the planting area has sharply decreased in recent years due to its poor appearance and taste quality, as well as low returns. Therefore, we collected and analyzed 334 early-season rice varieties released in the region from 2000 to 2022. To verify whether low-amylose content (L-Am) varieties can reduce chalkiness without compromising yield, two field experiments were conducted: a two-year consecutive experiment (2021–2022) using six representative varieties (low amylose, L-Am: 14.5–16.8%; medium-high amylose, MH-Am: 23.8–25.9%), and a one-year validation experiment (2024) utilizing 32 widely cultivated varieties. The results indicated that the amylose content (AC) of the 334 varieties showed a normal distribution, with varieties containing 18–20% AC being the most prevalent (23.6%), which resulted in L-Am varieties collectively accounting for 46.4%; additionally, AC was significantly positively correlated with chalky kernel rate (CKR) and chalkiness degree (CKD), and negatively correlated with panicles per m² and length–width ratio (LWR), but showed no correlation with yield. Similarly, L-Am and MH-Am varieties achieved comparable yields through compensatory adjustments in field experiments: L-Am varieties had 12.8–13.9% more panicles per m² but 3.6–7.3% lower 1000-grain weight. Moreover, L-Am varieties exhibited superior grain quality, with 70.8–73.5% and 54.0–62.1% lower CKR and CKD, respectively. Physiological analyses revealed that L-Am varieties exhibited a smaller maximum grain-filling rate (GFR_max) and amylose accumulation rate (GAmR_max), mean grain-filling rate (GFR_mean) and amylose accumulation rate (GAmR_mean), longer active grain-filling/amylose accumulation periods (D), and higher activities of soluble starch synthase (SSS) during grain-filling stages. These results demonstrate that early-season rice varieties with low AC tend to exhibit significantly lower chalkiness. Physiologically, this superior appearance quality is strongly associated with maintained yield through compensatory yield components and distinct starch synthesis kinetics, offering a practical strategy for enhancing both quality and productivity in early-season rice.