Abstract: In order to explore the effects of nitrogen (N) application rates on rice yield and grain-filling properties under different transplanting densities, this paper studied the population yield formation from the differences of grain-filling characteristics among different positions of grains by field experiments. The objective was to provide a theoretical basis for further improvement of rice yield potential. The experiment evaluated a split plot designed with different nitrogen application amounts as the main plots and transplanting density as the sub-plots. Richards equation  was used to describe the gain-filling process of superior and inferior rice gains. The results indicated that: ① The yields of N treatment were averagely increased by 36.6% and 34.6%, respectively, and the yield increased with increasing N application. Under high density (27×104 plants/hm2, 33×104 plants/hm2) conditions, N treatment could averagely increase the yield by 30.8% and 18.8%, respectively, but the seed-setting rate was decreased averagely by 2.0% and 1.6%, respectively, and the yield increased firstly then decreased with N application increase. ② The grain-filling characteristics showed that the nitrogen application increased the maximum grain-filling rate of the superior grains (GRmax), which was increased by 3.5% compared with that of N0 treatment, and increased firstly then decreased with N application increase. Transplanting density had significant effect on the average grain filling rate (GRmean). Under low density (15×104 plants/hm2, 21×104 plants/hm2) conditions, the GRmean of superior grains with N treatment was decreased by 2.1% and 3.1%, respectively, compared with that of N0 treatment. However, it was increased by 1.0% and 3.7%, respectively, under high density (27×104 plants/hm2, 33×104 plants/hm2) conditions. The GRmax and GRmean of inferior grains of N treatments were increased by 14.3% and 14.4%, respectively, compared to that of N0 treatment, and increased firstly then decreased with N application increase. ③The grain-filling characteristics of different stages indicated that the maximum contribution rates of superior and inferior grains were reached 58.6% and 57.3%, respectively, in the middle gain-filling stage. The average grain-filling rates (MGR) in the middle and late grain-filling stage were increased firstly then decreased with N application increase. The contribution rate and grain-filling lasting days were all increased with transplanting density increase. There was a significant positive correlation between 1 000-grain weight and GRmax and GRmean of inferior grains, but it had a significant negative correlation with the initial grain-filling potential (R0) and the active grain-filling period (D) of inferior grains. The seed-setting rate was negatively correlated with GRmean of inferior grains, while had a positive correlation with R0. The grain-filling rate and grain-filling lasting days were all improved by rational planting density and raising of nitrogen fertilization level (27×104 plants/hm2, 165kg/hm2). Whilst increasing the panicles per unit area, the individual grouting rate and effective grain-filling lasting days were all improved. Finally a high yield was formed, due to the plumpness of grain-filling.

Key words: rice yield, nitrogen application rate, transplanting density, grain-filling rate, effective grain-filling time

摘要： 为明确不同移栽密度条件下施氮水平对水稻籽粒产量及灌浆特性的影响，设计裂区试验，主处理为氮肥量，副处理为移栽密度，用Richards方程拟合水稻强、弱势粒的灌浆过程，从不同粒位籽粒灌浆特性间的差异认识群体产量构成，以期为进一步提高水稻生产潜力提供理论依据。结果表明：①低密度（15万株/hm2、21万株/hm2）条件下，与不施氮处理相比，施氮分别平均增产36.6%、34.6%，且随施氮水平的提高呈增加趋势。高密度条件下（27万株/hm2、33万株/hm2），施氮分别平均增产30.8%、18.8%，结实率分别平均降低了2.0%和1.6%，且产量随施氮水平的提高呈先增加后降低趋势。②灌浆特性结果显示，施氮提高了强势粒的最大灌浆速率（GRmax），与不施氮处理(N0)相比平均增加了3.5%，且随施氮水平的提高呈先增加后降低趋势。移栽密度对强势粒平均灌浆速率（GRmean）有明显影响，在低密度（15万株/hm2、21万株/hm2）条件下施氮处理强势粒GRmean与不施氮处理相比分别平均降低了2.1%、3.1%，而在高密度（27万株/hm2、33万株/hm2）条件下则分别平均增加了1.0%、3.7%；施氮显著提高了弱势粒的GRmax和GRmean，与不施氮处理相比分别平均增加了14.3%、14.4%，且随施氮水平的提高呈先增加后降低趋势。③灌浆阶段性特征显示，灌浆中期强、弱势粒物质积累对籽粒形成的贡献率均最大，分别为58.6%、57.3%。随着施氮水平的提高，中期和后期籽粒的平均灌浆速率（MGR）呈先增加后降低趋势。灌浆持续天数和灌浆贡献率均随着移栽密度的提升而增加。千粒重与弱势粒的GRmax和GRmean呈极显著正相关，与籽粒的起始势（R0）及弱势粒的灌浆活跃期（D）呈显著负相关。结实率与弱势粒GRmean呈显著负相关，与弱势粒的R0呈极显著正相关关系。通过合理密植，同时适当提高施氮水平（27万株/hm2，165 kg/hm2），在增加单位面积穗数的同时也提高了水稻个体灌浆速率、增加了有效灌浆持续天数，最终籽粒灌浆充实度好，形成高产。

关键词: 水稻产量, 施肥量, 移栽密度, 灌浆速率, 有效灌浆时间