Abstract:

Nitrogen needed by the growth and development of wheat is essential for grain yield formation. The content of chlorophyll, net photosynthetic rate in leaves, photosynthate accumulation and yield are increased with nitrogen fertilizer application. However, yield and nitrogen fertilizer use efficiency are decreased by excessive nitrogen application. Thus appropriate nitrogen rate is essential for profitable yields and efficient nitrogen utilization. The objectives of this study were to determine the effects of nitrogen fertilizer rate on photosynthetic character, sucrose synthesis in flag leaves and grain yield of wheat, for providing the theory basis on appropriate amount of nitrogen supplication in production。
The field experiments were carried out on high fertile soil with organic matter 12.94 g kg^-1, total nitrogen 0.78 g kg^-1, alkalihydrolysable nitrogen 84 mg kg^-1, available phosphorus 11.84 mg kg^-1 and available potassium 83 mg kg^-1 in Zhongcun Village, Longkou City, China, using the cultivar “Jimai 20” which has high yield and strong gluten potential. Five nitrogen treatments (N0, N1, N2, N3, N4, N5) were set, with 0, 96, 168, 240, and 276 kg N·ha^-1 respectively, using urea as the nitrogen fertilizer. Half of the nitrogen fertilizer was applied before sowing, the other half topdressed at jointing stage. The treatments were supplied with 105 kg P₂O₅ ha^-1 and 135 kg K₂O ha^-1 before sowing. Each treatment had three replicates, and the plot area was 3 m × 8 m = 24 m². The basic seedlings were 150 plant m^-2.
The results showed that intercellular CO₂ concentration decreased, transpiration rate, stomatal conductance, net photosynthetic rate, sucrose-phosphate synthase activity in flag leaves, sucrose synthesis, biological yield, grain yield and nitrogen fertilizer use efficiency increased with nitrogen applied form 96 to 168 kg ha^-1. Net photosynthetic rate, sucrose-phosphate synthase activity, sucrose content in flag leaves and biological yield increased significantly, but harvest index decreased, grain yield and nitrogen fertilizer use efficiency were not affected significantly by applying nitrogen of 240 kg ha^-1. Transpiration rate, stomatal conductance, stomatal limitation value and net photosynthetic rate in fag leaves decreased significantly, but intercellular CO₂ concentration increased, sucrose-phosphate synthase activity, sucrose content in flag leaves, biological yield, harvest index, grain yield and nitrogen fertilizer use efficiency decreased by excessive nitrogen applied with 275 kg ha^-1. The decrease of net photosynthetic rate mainly resulted from mesophyll factor. The appropriate amount of nitrogen application under the condition of this experiment with strong gluten cultivar “Jimai 20” is 168–240 kg ha^-1。

Key words: Winter wheat, Nitrogen fertilizer rate, Photosynthetic character, Sucrose, Yield