氮素是水稻取得高产的重要因素之一。除高产外，优质已成为当前水稻生产的又一迫切要求。灌浆期是水稻产量和品质形成的关键时期。而氮素对籼稻籽粒灌浆特性的影响及其与稻米品质的关系仍不清楚。通过大田栽培试验，研究了施氮条件下籽粒灌浆的关键特性与稻米研磨品质、外观品质和蒸煮食味品质的变化。结果表明，施氮延长了强、弱势粒灌浆的持续时间。弱势粒的平均灌浆速率（G_mean）和最大灌浆速率（G_max）与垩白粒率、垩白度和直链淀粉含量呈正相关关系。弱势粒达到最大灌浆速率的时间（T_max G）与糙米率、精米率和整精米率呈正相关关系。垩白粒率、垩白度与最高黏度、崩解值呈负相关关系。2016年和2017年两优培九和Y两优2号两个品种均在施氮后出现直链淀粉含量下降，粗蛋白含量增加。相关性分析说明，直链淀粉含量较低的Y两优2号蒸煮食味品质较好，可能是其弱势粒的最大灌浆速率（G_max）和平均灌浆速率（G_mean）高于两优培九所引起的。施氮后弱势籽粒灌浆时间的延长和达到最大灌浆速率时粒重的增加可以提高中籼稻的碾磨品质、外观品质和蒸煮食味品质。

We carried out a pool culture experiment to determine the optimal water treatment depth in loam and clay soils during the late growth stage of super rice.  Three controlled water depth treatments of 0–5, 0–10 and 0–15 cm below the soil surface were established using alternate wetting and drying irrigation, and the soil water potential (0 to –25 kPa) was measured at 5, 10 and 15 cm.  A 2-cm water layer was used as the control.  We measured soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and rice yield.  The results showed that the 0–5-cm water depth treatment significantly increased root antioxidant enzyme activities in loam soil compared with the control, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield did not differ from those of the control.  The 0–10- and 0–15-cm water depth treatments also increased root antioxidant enzyme activities, whereas soil enzyme activities, chlorophyll fluorescence parameters and yield decreased.  In clay soil, the soil enzyme activities, root antioxidant enzyme activities, chlorophyll fluorescence parameters, and yield did not change with the 0–5-cm water treatment, whereas the 0–10- and 0–15-cm water treatments improved these parameters.  Therefore, the appropriate depths for soil water during the late growth period of rice with a 0 to –25 kPa water potential were 5 cm in loam and 15 cm in clay soil.

Rice panicles are composed of many branches with two types of extreme grains, the superior and the inferior. Traditionally, it has been well accepted that earlier flowers result in superior grains and late flowers generate inferior grains. However, these correlations have never been strictly examined in practice. In order to determine the accurate relationship between superior and inferior grains and the flowering order, we localized all the seeds in a panicle in four distinct rice species and systematically documented the rice flowering order, flower locations and the final grain weight for their relationships. Our results demonstrated that the grain weight is more heavily determined by the position of the seeds than by the flowering order. Despite earlier flowering has a positive correlation with the grain weight in general, grains from flowers blooming on the second day after anthesis generally gained the highest weight. This suggests earlier flowers may not result in superior grains. Therefore, we concluded that superior and inferior grains, commonly determined by grain weight, are not fully correlated with the flowering order in rice. Following the order of the grain weight, the superior grains are generally localized at the middle parts of the primary branches, whereas inferior grains were mainly on the last two secondary branches of the lower half part of the panicle. In addition, the weight of inferior grains were affected by spikelet thinning and spraying with exogenous plant growth regulators, indicating that physiological incompetence might be the major reason for the occurrence of the inferior grains.