Effect of nitrogen application for spikelet promotion on growth and photosynthetic rate of canopy leaves in super hybrid rice

Resorting to two super rice hybrids (Guodao 6 and Liangyoupeijiu),the effect of 5 nitrogen levels (0,45, 90,135,180 kg/hm2),used at spikelet initiation stage on growth and photosynthetic rate of canopy leaves was studied.The results showed that:1) nitrogen level had a greater effect,on growth of the flag and second leaf from top, while the smaller effect on the third leaf. The length,width and area of the flag and second leaf from top increased with the increase of nitrogen level,and the nitrogen had a more evident effect on leaf length than width.The droopy index increased due to over-long leaf led to poor light penetration and air movement in canopy after flowering.2) The SPAD value of leaves increased from the flag leaf to the third leaf with the increasing level of spikelet promoting nitrogen,and the maximal SPAD value of flag leaf appeared at about 20 days from its outspreading. At late stage,the SPAD values of the second and third leaf from top decreased sharply under high nitrogen condition.3) Photosynthetic rate of the flag leaf could improve by increasing nitrogen application,and there was a positive correlation between SPAD values and photosynthetic rate of flag leaf after full heading stage.Photosynthetic rate of functional leaves from high to low were the flag leaf,the second leaf and the third leaf from top.