Fig. 2
Trends in grain yield with N fertilizer (YN, a), grain yield without N fertilizer (Y0, b), and increase in grain yield with N fertilizer (∆YN, c) of representative hybrid rice cultivars developed during different phases in China since 1996. Phases I, II, III, IV and V are 1996–2000, 2001–2005, 2006–2010, 2011–2015, and 2016–, respectively. Data were obtained from field experiments in which five representative hybrid rice cultivars of the five phases (i.e., Liangyoupeijiu, Y-liangyou 1, Y-liangyou 2, Y-liangyou 900, and Chaoyou 1000) were grown in Ningxiang, Hunan Province, China in 2015 (open circle) and 2016 (closed circle). Data in a and c are the means across two N fertilizer rates. Data points are means and standard deviations of three replications (b) or six replications (a and c). Trend (slope) in c is not statistically significant at the 0.05 probability level according to Student’s t test