Abstract:

The objective is to explore the effects of different nitrogen levels on photosynthesis of flag leaves, grain filling characteristics and yield of rice. The test took ‘Xindao 567’, ‘Xindao 568’ and ‘Xinkedao 31’ with short growth period as test materials, under direct seeding mode, three nitrogen levels were set up, 0 kg/hm², 255 kg/hm² and 300 kg/hm². The leaf photosynthetic rate, grain filling rate and yield after heading were determined, and the physiological mechanism of nitrogen fertilizer controlling yield was studied. The results showed that the yield of the three varieties increased first and then decreased along with the increase of nitrogen. High rate of leaf area and grain leaf ratio showed higher level under middle nitrogen, and they were lower under high nitrogen level. The flag leaf photosynthetic rate at grain filling stage was first increased and then decreased, and it was higher under middle nitrogen treatment than that of high nitrogen treatment. Superior and inferior grain filling rate had an open downward parabolic trend at the whole grain filling period, and the differences were higher between the peak and middle-late grain filling stage. The grain filling rate under zero nitrogen treatment and middle nitrogen treatment were higher than that of high nitrogen treatment, and the difference was small at later grain filling stage. Yield was positively correlated with flag leaf photosynthetic rate during grain filling stage, and negatively correlated with grain filling rate at early grain filling stage, and positively correlated at middle and late stage. The appropriate amount of nitrogen fertilizer is beneficial to improving the efficient leaf area rate, grain leaf ratio, and increasing flag leaf photosynthetic rate and grain filling rate of strong and weak grain in direct seeding rice, so as to promote the high yield of rice.

Key words: direct seeding mode, rice, photosynthetic, grain filling, nitrogen fertilizer, yield