Abstract: Waterlogging has great influence on yield reduction in winter wheat production in some areas of China. Nitrogen (N) application is believed to be able to improve dry matter translocation in wheat, as a result to increase final yield. In a field experiment across two growing seasons, we used winter wheat cultivar “Wanmai 54” to investigate the effect of waterlogging at booting stage and N fertilizing strategy on number and weight of grain at different spikelet positions and grain positions. Under both waterlogging and control (normal watering) conditions, we implemented four N application treatments with different N application ratios (total N amount of 240 kg ha^{-1 in all treatments) at land preparation, jointing, and booting stages (10:0:0 for N1, 7:3:0 for N2, 5:5:0 for N3, and 3:5:2 for N4). The results showed that seed-setting characteristics of main stem were superior to tiller spike. In the N1 treatment, the sterile spikelet per spike was significantly increased, and the grain number per spike was significantly decreased. Compared with N4 treatment, sterile spikelet per spike of N1 treatment increased by 25.5% and 29.8% in 2008–2009 and 2009–2010 growing seasons, respectively. The grain number per spike of N1 treatment decreased by 5.7%. Waterlogging had greater effect on the tiller spike than the main stem spike. Waterlogging at booting stage significantly increased sterile spikelet per spike by 10.6% and 4.5%, and the grain number per spike decreased by 2.8% and 1.4% in the two growing seasons, especially for spike with four grains on main stem and three grains per spike of tiller spike, the grain weight in the third and the fourth grain positions, the contribution rate of the third and the fourth grain weights to the grain weight per spike. With the delay of N fertilization, spikelet per spike, single weight per spike increased significantly, the sterile spikelet per spike decreased compared to the prior N fertilization treatments. Postponed N fertilization could compensate the decrease of spike with three and four grains and increase the grain weight in third and the fourth grain positions under waterlogged environment at booting stage, increase the contribution rate of the third and the fourth grains weight to the grain weight per spike. Therefore, with the postponed N fertilization, grain yield and spikelet grain number and grain weight at different spikelet of wheat were enhanced. Results indicate that postponed N fertilization alleviates the effect of waterlogging at booting stage on the seed-setting characterisitics of spike and single grain weight.}

Key words: Waterlogging, Nitrogen fertilization, Winter wheat, Seed-setting characteristics, Grain yield