Effect of panicle nitrogen on grain filling characteristics of high-yielding rice cultivars

• This experiment select three different panicle rice varieties, to reveal the superior and inferior spikelets filling mechanism and the difference of rice.
• This research finds out that panicle nitrogen fertilizer has a obvious control effect on rice inferior spikelets, especially on large panicle rice varieties.
• Proper panicle nitrogen fertilizer can obviously increase the average grain-filling speed, the biggest grain-filling rate and grain weight in active grain-filling period of inferior spikelets, and then to improve the final production.
• This research also finds out that different panicle type rice varieties grain-filling is different from panicle nitrogen fertilizer's corresponding time.

The effects of four levels of panicle nitrogen fertilizer on the grain filling characteristics of three rice (Oryza sativa L.) varieties (super japonica rice Ningjing 3, three-line japonica hybrid rice Changyou 3 and three-line indica–japonica hybrid rice Yongyou 12) were analyzed. The results showed that difference in time of maximum filling rate (Tmax) was the smallest between the superior and inferior spikelets of Ningjing 3, bigger between those of Changyou 3, the biggest between those of Yongyou 12. Ningjing 3 was of the synchronous grain-filling type, Yongyou 12 the asynchronous type, and the Changyou 3 the medium type. The grain filling rate, the initial filling power (R0), the maximum filling rate (Gmax), and the average filling rate (G) of the superior and inferior spikelets of the three varieties under the treatment of panicle N with the amount of 120 kg ha−1 (middle panicle N, shortened as NM) treatment were higher than those of other treatments. NM treatment led to the highest increase in grain weight at the middle stage of filling for all the three varieties. The treatment shortened the early and late stages of grain filling, but extended the middle stage when the filling rate was the highest. However, the middle stage of grain filling of Changyou 3 and Yongyou 12 was much more extended than that of Ningjing 3, indicating a better effect of N on hybrid rice varieties.