Effects of Sulfur on Photosynthesis Characteristics and Grain Yield of Winter Wheat under Different Nitrogen Application Rate

The experiment was conducted with soil available sulphur content of 22.78 mg/kg in 2003/2004 and 2004/2005 growing seasons.A total of eight fertilizeation treatments were implemented,2 N application rates(330、240 kg/hm2)and 4 S application rates(0,20,60,100 kg/hm2).The results indicated that fitting sulphur rate could improve the activity of nitrate reductase(NR),which was the key enzymes of nitrogen assimilation,and so improved the nitrogen assimilation ability.But under N330 supply levels,sulphur fertilization could reduce NR activity.Under the condition of nitrogen supply of 240 kg/hm2,sulphur fertilization could improve SPAD value of chlorophyll,and the more sulphur,the higher SPAD value.While under the condition of 330 kg/hm2, there was inhibition instead.The soluble protein content of flag leaf,under the different nitrogen supply levels,increased with the growth process,and drop promptly after reaching the maximum at anthesis.Under the same nitrogen supply level,its content increased with sulphur fertilization augment.The Photosynthesis Velocity(Pn) of flag leaf drop gradually since flowering.Under N330 supply level,Pn drop with sulphur fertilization,but gently.Under N240 supply level, increased with sulphur fertilization.Under the condition of N330 and N240,grains yield of N330S100,N330S60 and N300S20 had been improved by 28.6%,12.6% and 1.9% respectively;grains yield of N240S100,N240S60 and N240S20 improved by 25.7%,25.3% and 12.2% respectively.The level,but ears per 666.7 m2 and grains per ear hadn't.1 000-kernel weight of sulphur fertilization treatments had significant change under the same nitrogen supply.