Effect of Sowing Date on Photosynthetic Characteristics of Flag Leaf and Grain Yield in Winter Wheat Cultivars with Different Ear-types

Field experiments were conducted to evaluate the effects of 4 sowing dates on net photosynthetic rate of flag leaf and grain yield of winter wheat.Two wheat cultivars,Lankao Aizao 8 and Yumai 34,were used in the experiment.The result indicated that there was little difference in values of SPAD and Pn among the treatments of sowing date in early grain filling stage,but significant differences were found in late grain filling stage,of which treatment S1 decreased the most.This suggested that early sowing of wheat resulted in earlier leaf senescence,so as to depress the dry matter accumulation in late developmental stage.Sowing dates also affected the grain yield and its components,the highest and lowest grain yield being from the treatment S2 and S1 respectively.And significant effect of sowing date on spike number(P≤1%) and 1000-grain weight(P≤5%) were observed.The effect of sowing date on grain weight was was much greater in Lankao Aizao 8 than in Yumai 34.