Effects Of N Application At Later Stages On Population Quality And Yield Of Rice In Cold Area

In order to solve the problems in rice production, a study including five treatments with the same N application rate, but different application ratio and stages was conducted to investigate the effects of N application at later stages on nutrient absorption, population quality indexes, yield and N utilization efficiency.The results showed that there was a positive correlation between leaf N content at panicle initiation stage and grains per spike(P<0.01). In the phase from panicle initiation to flowering, N accumulation in rice plants accounts for 70% of the total accumulated N. N accumulations after heading in the treatments of N fertilization at later stages were improved by 7.2～81.9%, compared to FFP (Farmer's Fertilization Practice) treatment, and the difference was significant(P<0.05). There was a significant negative correlation between leaf nitrogen content during panicle initiation period and spike rate, which was one of the reasons that led to the low spike rate in FFP treatment. Spike rate in the treatments of N fertilization at later stage was 7.1～16.5 percentage points higher than FFP treatment, and the differences were significant(P<0.05).At heading date and filling stage, leaf area indexes in the treatments of N fertilization at later stages were 2.3～8.6 % and 10.5～27.1% higher than FFP treatment. Grain-leaf ratio in 6.5 :3.5 treatment at heading stage was the highest, up to 1.23 particle/cm~2, 9.8% higher than FFP treatment. There was a significant positive correlation between gain-leaf ratio at flling stage and rice yield (P<0.01). Culm-sheath weight per shoot in the treatments of N fertilization at later stages were 0.06～0.2g higher than FFP treatment, and the difference between 6.5 :3.5 treatment and FFP was significant (P<0.05). There was a significant positive correlation between the culm-sheath weight per shoot and grain number per spike, high photosynthetic leaf area and yield respectively (P<0.01). Dry matter accumulation after heading in the treatments of N fertilization at later stages increased by 6.5～24.6%, compared to FFP. The dry matter distributed mostly to the spike, which made the 1000-grain weight of rice improved by 0.28～0.5g, and seed setting rate elevated by 1.7～2.4%. Meanwhile, grain number per spike was increased by 1.7～2.4 %, and the yield was enhanced by 1.9～18.4%. Among the treatments, the yield for 6.5 :3.5 treatment was the highest, up to 12.2 t/ha.Compared to FFP treatment, recovery N use efficiency in the treatments of N fertilization at later stages were improved by 13～64.5%, and agronomic N use efficiency was increased by 4.5～19.2 kg/kg. N utilization efficiency in 6.5 :3.5 treatment was 49.1%, the highest, and the difference was significant compared with FFP treatment(P<0.05). Agronomic efficiency was 48.1 kg/kg, also the highest among all treatments, and the difference was significant(P<0.01)compared with FFP treatment.