Effects Of N Application At Later Stage On Photosynthetic Characteristics Of Rice After Heading In Cold Area

A plot experiment was designed to study the effect of N application at later stage (INM: the ratio of panicle fertilizer is 35%) on photosynthetic characteristics after heading in relationship with population quality, dry matter accumulation and yield of rice to provide a theoretical basis for fertilization. The plot experiment included different levels of N (105 kg·hm-2 and 135 kg·hm-2), compared with farmers′fertilization practice (FFP: the ratio of panicle fertilizer is 15%). Photosynthetic characteristics of function-leaves, population quality and dry matter weight were analyzed.The main results are as follows:There were significantly positive correlations(P<0.01)between photosynthetic rate and LMA at the stage of 20 days after heading(filling stage); there were significantly positive correlations(P<0.05) between photosynthetic rate and chlorophyll content. INM increased stomatal conductance, LMA and chlorophyll content, so photosynthetic rate was increased. Compared with FFP1, INM1 increased photosynthetic rate by 3.2%~9.98%; compared with FFP2, INM2 increased photosynthetic rate by 5.9%~9.9%. And with the improvement of N fertilizer, the photosynthetic rate increased.There were significantly curve correlation (P<0.01) between LAI and yield, and significantly positive correlations(P<0.01) between culm-sheath dry weight and yield at heading stage; there were significantly positive correlations(P<0.01) between LAI and yield, and significantly positive correlations(P<0.01) between leaf-grain ratio and yield at the stage of 20 days after heading. Compared with FFP, INM increased LAI in the appropriate leaf area at different stages after heading, increased culm-sheath and grain-leaf ratio at heading stage. Compared with FFP1, INM1 increased earbearing tiller rate by 5.6% and transmittance by 63.6%~67.9%, the statistical analysis showed significant difference at 0.05 level; compared with FFP2, INM2 increased earbearing tiller rate by 5.2% and transmittance by 34.8%~60.0%. So N application at later stage significantly improved population quality and provided a basis for high yield.Compared with FFP1, INM1 increased dry matter accumulation after heading by 17.6%(P<0.05); compared with FFP2, INM2 increased dry matter accumulation after heading by 6.1%. As for panicle accumulation and total accumulation, INM1 was more than FFP1, and INM2 was more than FFP2. Compared with FFP1, INM1 increased translocation ratio of stem and leaf by 54.3%(P <0.01); compared with FFP2, INM2 increased translocation ratio of stem and leaf by 2.3%. Compared with FFP1, INM1 increased contribution ratio of stem and leaf by 30.0%(P<0.01); compared with FFP2, INM2 decreased contribution ratio of stem and leaf by 4.1%.Under appropriate N level, N application at later stage increased translocation ratio of stem and leaf and contribution ratio of stem and leaf. So N application at later stage improved photosynthetic material translocation after heading.Bscause of the effect of lodging at later stage on grain-filling, filled grain rate and 1000-grain weight of INM2 and FFP2 were low. Compared with FFP1, INM1 increased grains per panicle by 5.9 grains / panicle and increased 1000-grain weight by 0.81g, but there was no significantly difference in productive panicles and filled grain rate. Compared with FFP2, INM2 increased grains per panicle by 4.8 grains / panicle, but there was no significantly difference in productive panicles, filled grain rate and 1000-grain weight. Compared with FFP1 and FFP2, INM1 and INM2 increased yield by 12.3% and 12.6%( P<0.05), reaching 9.74t·hm-2 and 9.77t·hm-2. Compared with FFP, N application at later stage increased recovery N use efficiency by 21.8%~40.8% and increased agronomic N use efficiency by 37.5%~38.5%.