Effects of excessive nitrogen supply on productivity of winter wheat
过量施氮对冬小麦生产力的影响

Aims Integrated research on the effect of N supply on successive levels from leaf to canopy would be helpful to improve the field N management in winter wheat production areas in China. Methods Field experiments were conducted under 5 N levels: 0, 70, 140, 210 and 280 kg N·hm–2. Four levels of productivity were measured: leaf photosynthetic rate (Aleaf) and canopy photosynthetic rate (Acanopy) measured at the stages of booting, flowering and grain-filling, crop growth rate (CGR) measured during the stages of setting-flowering and flowering-ripening and grain yield (GY) measured at the stage of harvesting. Important findings Results show that Aleaf, Acanopy and CGR have increasing patterns at all stages when N supply increases from 0 to 210 kg N·hm–2. When N supply increases from 210 to 280 kg N·hm–2, GY has no significant variation; however, the Aleaf and Acanopy during the grain-filling stage and the CGR during the flowering-ripening stage decrease. These results indicate that: 1) excessive N supply of 280 kg N·hm–2 can decrease the productivity of winter wheat over leaf, canopy and biomass levels and inhibit GY increasing; 2) the negative effect of excessive N supply is readily demonstrated during the stage of grain-filling; and 3) Acanopy is more capable of detecting the negative effect of excessive N supply than Aleaf, CGR and GY.