| Wuchang of Heilongjiang Province is a famous rice planting base in China.High yield rice varieties account for about 40%in this region.In the past,most of the studies focused on good-quality rice varieties,and the appropriate amount of nitrogen application for high-yield rice varieties was not clear.A field plot experiment was conducted from 2018 to 2019,the rice variety was Songjing No.3,a high-yield rice variety widely planting in this region,and five nitrogen levels,0,75,105,135,and 165 kg·N·hm-2 were set.Rice tillers,dry matter accumulation,nitrogen accumulation,yield,and nitrogen efficiency were determined.The effects of nitrogen amount on rice yield and nitrogen efficiency were studied in order to provide theoretical basis for reasonable nitrogen application of high-yield rice in Wuchang City.The main research results are as follows:Nitrogen application could promote the occurrence of rice tillers.The tiller number did not increase significantly,and the earbearing tiller rate showed a stable trend when the nitrogen application amount reached 135 kg·N·hm-2.With the increase of nitrogen application,the number of tillers significantly increased by 49.54%-65.15%,62.36%-82.90%and 63.13%-87.92%at jointing,heading and maturity stages,respectively,and the earb earing tiller rate was increased by12.99%-13.51%（P<0.05）.Nitrogen application mainly affected the tillers at the 10-leaf stage.At this stage compared with the treatment without nitrogen application,the earbearing tiller rate increased by 39.46%on average after nitrogen application（P<0.05）,and the nitrogen application amount at other stages had little effect on the earbearing tiller rate.With the increase of nitrogen application,the dry matter accumulation at jointing stage,heading stage and maturity stage N165 increased by 9.70%-52.3%,13.4%-52.8%and22.7%-25.9%compared to N75.Corresponding to 63.8%-81.32%,60.5%-98.9%and 48.3%-68.5%increase in nitrogen accumulation,respectively.Nitrogen application significantly increased plant nitrogen content and nitrogen accumulation,and nitrogen accumulation was in a parabolic relationship with dry matter accumulation,so more nitrogen is not better.Nitrogen amount had a great influence on the distribution of dry matter after heading.Both dry matter and nitrogen allocation rate at the heading stage were more variable in the leaves,and dry matter and nitrogen allocation in the stalk and spike were more variable in 2018,the proportion of dry matter allocated and the proportion of nitrogen allocated to N165 treated stems in 2018 increased by 10.94%and25.39%compared to N0.The proportion of dry matter allocated and the proportion of nitrogen allocated to N165 treated spikes in 2018 decreased by 28.52%and 36.38%compared to N0.The corresponding differences between treatments in 2019 were not significant.The dry matter and nitrogen allocation rate varied less at the maturity stage relative to the heading stage.The dry matter and nitrogen translocation and translocation efficiency translocation contributions were highest in N75 in both years,and the dry matter and nitrogen assimilation contributions were lowest in N75 in both years after heading.The effect of nitrogen application on yield increase was significant.The yield,spikelet number per unit area and 1000-grain weight increased with increasing nitrogen,and the nitrogen application amount reached a certain amount,the yield increased not significantly（2019）,and the grain filling rate decreased with increasing nitrogen.Rice yield and spikelet number per unit area increased.Rice yield increased 64.20%–87.91%（P<0.05）,and spikelet number increased77.87%–96.63%（P<0.05）compared to no nitrogen application.There were significant differences in 1000-grain weight between nitrogen and non-nitrogen treatments.Nitrogen fertilizer input increased more than 60 kg·hm-2,grain filling rate decreased significantly.The relationship between nitrogen and yield was in accordance with the linear plus platform model.The nitrogen application at the turning point was 137.5 kg·hm-2.The nitrogen recovery efficiency had no significant change or increased significantly with the increase of nitrogen amount,which had interannual differences.With the increase of nitrogen fertilizer application rate,nitrogen physiological utilization rate,agronomic utilization rate（excep t for 2019）,and partial factor productivity decreased significantly.The nitrogen application amount above 137.5 kg·hm-2 will not cause yield reduction,but in the early low temperature year（2019）will cause a significant decrease of nitrogen agronomic efficiency.According to the principal component analysis,yield,number of tillers,dry matter accumulation,nitrogen accumulation,spikelet number per unit area and 1000-grain weight were positively correlated,and grain filling rate was negatively correlated with other indicators.The overall score was N165>N135>N105>N75>N0.In summary,for high-yield rice varieties with fertilizer tolerance,the increase of nitrogen application rate is not easy to cause yield reduction,but may cause nitrogen efficiency reduction.Appropriate nitrogen application is more critical to achieve the unity of high yield and nitrogen efficiency of high-yield rice varieties. |
