Combined effect of shading time and nitrogen level on grain filling and grain quality in japonica super rice

摘要

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 (GRmean and GRmax).In inferior grains,grain weight and GRmean had a tendency of 150N NS＞150N BH＞150N AH.Under shaded conditions,300N decreased the grain weight due to lower GRmean 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.