Effects of Application of Nitrogen as Panicle-promoting Fertilizer on Seed Setting and Grain Quality of Rice under High Temperature Stress

Effects of application of nitrogen as panicle-promoting fertilizer on grain yield and quality was studied with two mid-season rice cultivars,Huhan 15(indica)and Yangjing 4038(japonica)grown in pots as materials under three nitrogen fertilizer levels,low nitrogen level(LN,0.5g urea per pot),medium nitrogen level(MN,1.0g urea per pot),and high nitrogen level(HN,2.0g urea per pot)at the panicle initiation stage under high temperature.Both high temperature(mean temperature during the day/night at 35.1℃/20.8℃)and normal temperature(mean temperature during the day/night at 29.0℃/20.8℃)treatments were conducted during heading and grain filling.The grain yield and rice quality were investigated under these treatments.The results showed that at the same temperature,especially under high temperature,compared with the LN,the MN and HN significantly increased spikelet number per panicle,seed-setting rate,1000-grain weight,grain yield,head rice rate and short chain percentage in debranched amylopectin,and reduced chalky grains and long chain in debranched amylopectin,especially at MN.Application of paniclepromoting fertilizer also increased the photosynthetic rate of flag leaf,root oxidation activity,and activities of the key enzymes involved in sucrose-to-starch metabolic pathway in grains in the two cultivars.These results indicate that proper application of nitrogen as panicle fertilizer could maintain a higher grain yield and better quality of rice when subjected to high temperature during heading and grain filling,and increases in root and shoot activities contribute to the reducing adverse effects of high temperature on rice yield and quality.