Abstract: 【Objective】 The sugar-nitrogen characteristics of wheat at yield level of 9 000 kg•hm-2 following rice were studied. In addition, the sugar-nitrogen nutrition diagnosis indexes for wheat at yield level of 9 000 kg•hm-2 were suggested. 【Method】 Wheat populations at two different yield levels in rice-wheat rotation, including ＜9 000 kg•hm-2 population (hereinafter as HY) and ≥9 000 kg•hm-2 population (hereinafter as SHY), were established by agronomic management of the medium-gluten wheat, Yangmai 20 (Triticum aestivum L.). From 2010 to 2012, field experiments were conducted as split-plot design at 16 combinations of two applications of nitrogen amount (210 kg•hm-2 and 262.5 kg•hm-2), two nitrogen applied ratios of basis﹕tillering﹕elongation﹕booting (3﹕1﹕3﹕3 and 5﹕1﹕2﹕2), and four nitrogen topdressing stages (flag leaf stage, booting stage, heading stage and anthesis). The dynamics of soluble sugar content, nitrogen content and soluble sugar to nitrogen ratio (hereinafter as C, N and C/N) in plant population of different yield levels were analyzed. And at different growth stages, the relationship between plant C, N and C/N and grain yield were analyzed, respectively. In addition, the sugar-nitrogen nutrition diagnosis indexes for wheat at yield level of 9 000 kg•hm-2 were suggested. 【Result】 As the developmental process goes on, the plants C and C/N had two peak values at the beginning of over-wintering stage and at stage from booting to anthesis, and a low value at green-turning stage. Then, the plants C and C/N showed a gradual decrease after anthesis. The plants N, however, showed a gradual decrease during the growth period - rapid decrease during the period between the beginning of over wintering stage and elongation stage, slow decrease during the period between elongation stage and booting stage, and slow decrease during the period between booting stage and maturity stage. In SHY plants, C and N at booting and N at anthesis were significantly higher than those of HY. But C at maturity was significantly lower than those of HY in 2010-2011, and not-significantly lower than those of HY in 2011-2012. In addition, C/N at maturity was significantly lower than those of HY. Plants C and N at booting stage and N at anthesis were in a positive linear correlation with grain yield. Plants C and N at milk-ripe stage were in a parabolic cure relationship with grain yield. Plants C at maturity were in a negative linear correlation with grain yield. The sugar-nitrogen nutrition diagnosis indexes for the population of about 9 000 kg•hm-2 were suggested. At the stages of booting, anthesis, milk-ripe and maturity, C were 14.56%-16.78%, 14.52%-16.82%, 10.59%-11.23% and 1.62%-1.76%, respectively, N were 1.55%-1.64%, 1.47%-1.57%, 1.28%-1.30% and 1.15%-1.20%, respectively, and C/N were 9.37-10.25, 9.80-10.69, 8.29-8.77 and 1.41-1.48, respectively. 【Conclusion】 Compared with HY, from the beginning of over wintering stage to elongation, C and N in SHY plants were generally high, and C/N was relatively suitable. From booting stage to anthesis, C and N in SHY plants were significantly higher. After anthesis, SHY plants could accumulate more sugar and had a higher conversion rate of sugar to grain yield as compared with HY.

Key words: wheat following rice , high-yield , sugar-nitrogen metabolism , characteristics