Although a lot of researches have been done on yield characteristics of japonica/indica hybrid rice, there is little information on differences of yield characteristics between different types of hybrid.  To determine common characteristics of japonica/indica hybrid rice (JIHR) and identify the differences between different types of JIHR, the present study assessed yield characteristics, such as panicle trait, leaf area index (LAI), above-ground biomass accumulation, and nitrogen absorption and utilization, among three types of cultivar of JIHR.  In our field experiments, three types of JIHR, e.g., Yongyou, Chunyou and Jiayouzhongke, were divided, and each of them has two cultivars, which were used as materials, meanwhile, using conventional japonica rice (CJR) Wuyingjing 31 and Sujing 9 were as controls.  The results showed that the mean yield of those JIHR was above 12 t ha^–1 in 2017 and 2018, and was 31.9 and 32.2%, respectively higher than that of CJR in the two years.  Spikelet number per panicle of JIHR resulted in high yield.  Higher yield of JIHR was likely contributed to greater panicle number and more spikelets per panicle.  Higher yielding JIHR showed stronger tillering capacity, larger LAI and above-ground biomass accumulation from jointing to heading stages, which likely contributed to the higher number of spikelets per panicle.  The long duration from heading to maturity stages allowed more nitrogen accumulation of higher yielding JIHR.

There is limited information about the combined effect of shading time and nitrogen (N) on grain filling and quality of rice.  Therefore, two japonica super rice cultivars, Nanjing 44 and Ningjing 3, were used to study the effect of shading time and N level on the characteristics of rice panicle and grain filling as well as the corresponding yield and quality.  At a low N level (150 kg N ha^–1, 150N), grain yield decreased (by 21.07–26.07%) under the treatment of 20 days of shading before heading (BH) compared with the no shading (NS) treatment.  These decreases occurred because of shortened panicle length, decreased number of primary and secondary branches, as well as the grain number and weight per panicle.  At 150N, in the treatment of 20 days of shading after heading (AH), grain yield also decreased (by 9.46–10.60%) due to the lower grain weight per panicle.  The interaction of shading and N level had a significant effect on the number of primary and secondary branches.  A high level of N (300 kg N ha^–1, 300N) could offset the negative effect of shading on the number of secondary branches and grain weight per panicle, and consequently increased the grain yield in both shading treatments.  In superior grains, compared with 150N NS, the time to reach 99% of the grain weight (T₉₉) was shortened by 1.6 to 1.7 days, and the grain weight was decreased by 4.18–5.91% in 150N BH.  In 150N AH, the grain weight was 13.39–13.92% lower than that in 150N NS due to the slow mean and the maximum grain-filling rate (GR_mean and GR_max).  In inferior grains, grain weight and GR_mean had a tendency of 150N NS>150N BH>150N AH.  Under shaded conditions, 300N decreased the grain weight due to lower GR_mean both in superior and inferior grains.  Compared with 150N NS, the milling and appearance qualities as well as eating and cooking quality were all decreased in 150N BH and 150N AH.  Shading with the high level of 300N improved the milling quality and decreased the number of chalky rice kernels, but the eating and cooking quality was reduced with increased chalky area and overall chalkiness.  Therefore, in the case of short term shading, appropriate N fertilizer could be used to improve the yield and milling quality of rice, but limited application of N fertilizer is recommended to achieve good eating and cooking quality of rice.