Yield performance and nitrogen use characteristics of three low-cadmium rice varieties developed via OsNRAMP5 mutation

Excessive grain cadmium (Cd) accumulation is a pervasive problem in many rice-growing regions globally, including Hunan Province, China. A notable recent advance in addressing this issue is the development of several low-Cd rice varieties in Hunan through targeted modification of the Cd-transporter OsNRAMP5 . However, the agronomic characteristics of these varieties beyond low grain Cd accumulation remain inadequately characterized. This study aimed to evaluate the yield performance and nitrogen (N) use characteristics of recently developed low-Cd rice varieties. Field experiments were conducted over two years to evaluate grain yield and N use efficiency under five N application rates (0, 90, 120, 150, and 180 kg ha –1 ), as well as the responses of grain yield and total N uptake to N application rate, in three recently developed low-Cd rice varieties—Zhongan 2 (ZA2), Zhongan 7 (ZA7), and Zhonganzao 35 (ZAZ35)—and a widely grown non-low-Cd variety, Zhongzao 35 (ZZ35). ZA2 achieved average grain yields comparable to ZZ35 across all five N application rates over the two years, whereas ZA7 and ZAZ35 generally produced lower average yields than ZZ35 in one or both years. Most N use efficiency parameters of the three low-Cd varieties, calculated using fixed N application rates, were either comparable to or not consistently different from those of ZZ35 over the two years. All three low-Cd varieties exhibited a significant quadratic relationship between grain yield and N application rate, whereas ZZ35 displayed a significant linear increase in grain yield with increasing N rates. ZA2 achieved a 15% higher maximum grain yield at a 16% lower N application rate than ZA7, and a similar maximum grain yield at a 24% lower N application rate compared with ZAZ35. At maximum grain yield, ZA2 achieved 11%–14%, 20%–32%, 23%–26%, and 32%–36% higher internal N use efficiency, physiological N use efficiency, agronomic N use efficiency, and partial factor productivity of applied N, respectively, compared with ZA7 and ZAZ35. These results clarify the yield performance and N use characteristics of the low-Cd rice varieties and indicate that ZA2, combining high grain yield with efficient N utilization, is a promising option for cultivation on Cd-contaminated soils.