Search

Panicle nitrogen fertilizer amount and shading during grain filling period directly and obviously regulated the relationship between carbon and nitrogen metabolism of rice grains by affecting leaf photosynthesis and plant nitrogen nutrition, which would be benefit to forming different characteristics of rice quality. In order to investigate the combined effect between panicle nitrogen fertilizer amount and shading during grain filling period on quality of conventional japonica rice, field experiments were carried out with three panicle nitrogen application treatments of 40.5 kg hm-2 (N1), 81.0 kg hm-2 (N2) and 121.5 kg hm-2 (N3) at the same amount of basal and tilling fertilizers, and two artificial shading treatments of 100% natural light (S0) and 50% natural light (S50) during grain filling period in 2019 and 2020. The quality characteristics of conventional japonica rice Huaidao 5, Nanjing 9108, and Yangnongxiang 28 were determined under different light and nitrogen conditions during grain filling period. Results showed that with the increase of panicle nitrogen fertilizer amount, the brown rice rate, milled rice rate, and heading rice rate firstly increased and then decreased under S0 and decreased under S50. The brown rice rate, milled rice rate and heading rice rate of S0 were significantly higher than S50, while the processing quality of S0N2 with higher heading rice rate was the best among all treatments. The chalkiness grain percentage and chalkiness degree of rice had a trend of S50N3 > S50N2 > S50N1 > S0N3 > S0N2 > S0N1. Therefore, the increase of panicle nitrogen fertilizer amount and the shading during grain filling period had a cumulative effect on the increase of chalkiness grain rate and chalkiness degree of rice. Both the increase of panicle nitrogen fertilizer amount and shading during grain filling period decreased the amylose content and gel consistency, but increased the protein content. And the variation coefficient of glutelin was higher than other protein components among treatments. The rice taste value was decreased with the increase of panicle nitrogen fertilizer amount and the shading during grain filling period, while the direct influence of taste characteristic value on taste value was different among rice varieties. The peak viscosity and breakdown viscosity of rice starch decreased with the increase of panicle nitrogen fertilizer amount and the shading during grain filling period, while the setback viscosity increased. And the combination of light and nitrogen increased the difference of the above viscosity indexes among treatments. Based on the ratio of amylose content to protein content under different treatments of panicle nitrogen fertilizer amount and shading during grain filling period, the carbon and nitrogen metabolism ability of plants at grain filling stage were changed. In addition, the amylose content and protein content were significantly negatively correlated with taste value, while the correlation coefficient of protein was bigger than amylose content. Thus, an appropriate reduction of panicle nitrogen application fertilizer amount was beneficial to the improvement of rice processing quality, appearance quality and cooking and eating quality at grain filling stage with shading. The reduction of amylose content and especially the reduction of protein content might be an effective way to improve rice taste. The results would provide scientific support for the innovation of high yield and good taste rice cultivation techniques. [ABSTRACT FROM AUTHOR]