Agronomic and Physiological Performances of High-Quality Indica Rice under Moderate and High-Nitrogen Conditions in Southern China

High-quality (i.e., higher appearance and eating quality) rice (Oryza sativa L.) is being increasingly and widely planted in China with the improvement of people's living standards and the achievement of rice breeding efforts in recent years. However, the agronomic and physiological performances of high-quality indica rice (HQIR) under different nitrogen (N) application conditions in southern China are little known. Two-year consecutive field experiments were conducted with two HQIR and two ordinary-quality indica rice (OQIR) varieties under moderate and high-N application rates, with yield and yield components, biomass, N uptake, and their related traits, being investigated. We found that grain yields of HQIR were slightly decreased, but grain yields of OQIR were significantly increased by 7.0-9.6% under a high N rate, compared with a moderate N rate within two years. Thereby, OQIR produced a 5.7-14.7% and 18.7-25.6% higher grain yield than HQIR under moderate and high N rates, respectively. The different responses of grain yield to N application rates were mainly due to a decreased grain setting rate in HQIR and increased spikelets m(-2) in OQIR under a high N rate. Furthermore, a high N rate significantly reduced pre-anthesis AE (apparent exportation of pre-anthesis stem and leaf blade dry matter) and improved the grain-leaf area ratio, while it did not increase post-anthesis dry matter, compared with a moderate N rate in HQIR, which might result in carbon-metabolic deterioration, an imbalance of the source-sink relationship and, subsequently, a lower supply of carbohydrate in panicle. Our results suggest that a moderate N rate (165 kg N ha(-1)) is beneficial for the HQIR varieties to balance the maximum grain yield and high quality in southern China.