The Effects Of Nitrogen Application Rates On Rice Grain Yield And Nitrogen Use Efficiency In Different Rice Production Regions Of Hubei Province

Nitrogen(N) fertilizer plays a critical role in rice production. Nitrogen use efficiency(NUE) is influenced by N application, grain yield and the environmental factors. Therefore, an understanding of the effects of different environmental factors conditions on NUE and the underlying mechanism could be useful for optimizing N fertilizer management in rice production for high yield and high efficiency. In 2014 and 2015, field experiments were conducted at three sites, Wen’an town in Zhijiang, Junchuan town in Suixian, and Huaqiao town in Huanggang, Hubei Province. The split plot design was adopted, with three N treatments(N1, 0 kg N ha-1; N2, 120 kg N ha-1; N3, 210 kg N ha-1) as main plot and six cultivars(Huanghuazhan, LvdaoQ7, Yangdao6, Y Liangyou1, Liangyoupeijiu, Luoyou10) as subplot. The biomass, grain yield and its components, plant N content, NUE were determined under different environmental conditions. The main objectives of this study are to:(1) compare the differences of rice yield and NUE under different N treatments and different rice production regions;(2) explore the effect of environmental factors on rice yield and NUE. The main results of the present study are listed as follows:(1) The grain yield in Suixian was the highest than those in the Zhijiang and Wuxue, which mainly due to the large spikelets per panicle in Suixian. The grain yield under zero-N treatment was the lowest, and grain yields had no significant difference between medium-N and high-N treatments. There was a positive correlation between grain yield and temperature difference during the rice growth period. Suixian had larger temperature difference. The favorable environmental factors in Suixian increased dry matter accumulation, panicles per hill and spikelets per panicle, which together resulted in the higher yield in Suixian than those in the other two sites. Grain yield was higher in 2015 than that in 2014 under each N treatment in Suixian, which could be mainly attributed to the large temperature difference(about 10 ℃) and consequently more dry matter accumulation in Suixian.(2) The physiological nitrogen use efficiency(PE) and nitrogen use efficiency for grain yield(NUEg) had the high correlation with plant N uptake, while physiological nitrogen use efficiency(PE) showed high correlation with yield under high N treatment in this study. The PE, NUEg, partial factor productivity of applied nitrogen(PFP) were decreased with the increase of N application rate in each site, which was mainly due to the similar grain yields between medium-N and high-N treatments, but significant difference was found in plant N uptake. The difference of N uptake was due to the difference in translocation of pre-anthesis nitrogen(TN) among the different N treatments.(2) Effects of N application rates on nitrogen recovery efficiency(RE) were different in Suixian from the other two sites. In Suixian, RE was increased with the increase of N application rate, which was mainly due to higher plant N uptake. Suixian had more increase in N uptake with the increase in N application rate, compared with the other two sites. The plant N uptake and post-anthesis nitrogen accumulation(WrN) were the largest, while the N translocation ratio(NTR) was lower in Suixian.(3) The PE, NUEg, and PFP were influenced by active accumulation temperature and total radiation during the rice growth period among the three experimental sites. There were negative correlations of PE, NUEg, PFP with the total radiation, accumulated temperature during the rice growth period in two years. The correlation between RE and temperature difference was positive, and RE was negatively correlated with total radiation during rice growth period in 2014. However, RE was negatively correlated with temperature difference, and there was positive correlation between RE and daily average radiation during the rice growth period in 2015.(4) In Suixian, RE was increased with the increase of N application rate in inbred varieties, however, hybrid varieties showed a different trend in 2014. By contrary, RE was decreased with the increased of N application rate in inbred varieties, however, hybrid varieties showed a different trend in 2015. That was due to that the plant N uptake performed different trends between inbred varieties and hybrid varieties. The plant N content of inbred varieties was higher than that of hybrid varieties in Suixian. With the increasing of N rate, inbred varieties had more increases in the plant N content that hybrid varieties in Wuxue. But biomass and grain yield of inbred varieties were lower than that of hybrid varieties. The NHI of inbred varieties was lower than that in hybrid varieties, and the inbred varieties stored more N in stem sheath and leaf, leading to lower rice NUEg.In conclusion, the difference of NUE among the three experimental sites and N treatments were determined by grain yield or plant N uptake. The large temperature difference(around 10℃) was conductive to dry matter accumulation, N uptake and grain filling in different rice production regions. But the daily lowest temperature(<20℃) could influence the grain yield formation and NUE at heading stage to mature stage. Therefore, we should focus on temperature conditions(the low temperature, temperature difference) and combined with light, rainfall and other conditions in different rice production regions. Then we could through reasonable field management to achieve the purpose of high production and high efficiency.