Elucidating Variations in Nitrogen Requirement According to Yield, Variety and Cropping System for Chinese Rice Production

Better understanding of the factors that influence crop nitrogen (N) requirement plays an important role in improving regional N recommendations for rice (Oryza sativa L.) production. We collected data from 1 280 plot-level measurements in different reaches of the Yangtze River, China to determine which factors contributed to variability in N requirement in rice. Yield, variety, and cropping system were significantly related to N requirement. The N requirement remained consistent at about 18.6 kg N Mg−1 grain as grain yield increased from 7 to 9 Mg ha−1, then decreased to 18.1, 16.9, and 15.9 kg N Mg−1 grain as yield increased to 9-10, 10-11, and > 11 Mg ha−1, respectively. The decreased requirement for N with increasing yield was attributable to declining N concentrations in grain and straw and increased harvest index. Super rice variety had lower N requirement (17.7 kg N Mg−1 grain) than ordinary inbred and hybrid varieties (18.5 and 18.3 kg N Mg−1 grain, respectively), which was a result of lower grain and straw N concentrations of super rice. The N requirements were 19.2, 17.8, and 17.5 kg N Mg−1 grain for early, middle, and late rice cropping systems, respectively. In conclusion, the rice N requirement was affected by multiple factors, including yield, variety, and cropping system, all of which should be considered when planning for optimal N management.