Yield Formation Characteristics And Nitrogen Use Efficiency Of Low-nitrogen Tolerant Rice Varieties

Rice is one of the main food crops in China.Increasing nitrogen fertilizer application within a certain range can significantly increase rice yield.However,excessive nitrogen fertilizer application will bring a series of problems,such as rice lodging and environmental pollution.Therefore,how to improve nitrogen utilization efficiency and alleviate the contradiction between agricultural production and the environment is the focus of modern rice high-yield and high-efficiency cultivation research.In order to provide a reference for the selection of low-nitrogen tolerant varieties in cultivation,and to provide theoretical basis for breeders to select new high-yield and low-nitrogen tolerant rice varieties.A field experiment using a low-nitrogen tolerant rice variety（Deyou 4727）and a control variety（Y-liangyou 900）as materials was carried out in Yong an,Liu yang in 2020 and 2021.Four nitrogen treatments(0,120,180 and 240 kg N hm^-2)were conducted.The experiment was arranged in split-plot design with nitrogen fertilizer treatment as the main plot and varieties as the subplots.The yield formation characteristics and nitrogen fertilizer use efficiency of low-nitrogen tolerant rice varieties were studied.The main results were as follows:1.Yield formation characteristics of low-nitrogen tolerant rice varietiesUnder no nitrogen application(0 kg N hm^-2,N0)and low nitrogen conditions(120 kg N hm^-2,N120):（1）The yield of Deyou 4727 was higher than that of Y-liangyou 900,and under the N0 treatment,the two-year average yield of Deyou 4727 was 7.15 t hm^-2,which was20.68%higher than that of Y-liangyou 900.Under N120 treatment,the yield of Deyou 4727was 8.59 t hm^-2,which was 4.38%higher than that of Y-liangyou 900;（2）Panicles,spikelet filling and 1000-grain weight of Deyou 4727 were significantly higher than those of Y-liangyou 900,and the performance was consistent in two years;（3）There was no significant difference in dry matter accumulation between Deyou 4727 and Y-liangyou 900,but the harvest index was higher than that of Y-liangyou 900,with an average increase of14.77%（N0）and 7.78%（N120）in two years;（4）The radiation interception amount of Deyou 4727 is higher than that of Y-liangyou 900,but the radiation utilization rate is lower than that of Y-liangyou 900.With the increase of nitrogen application rate(from 0 kg N hm^-2to 240 kg N hm^-2),the increased yield of Deyou 4727 was small.In 2020,the yield of Deyou 4727 and Y-liangyou900 increased by 31.40%and 54.40%,respectively,and in 2021 increased by 14.11%and41.65%,respectively.The harvest index decreased with the increase of nitrogen fertilizer application rate,Deyou 4727 decreased by 8.91%on average in two years,and the decreased rate was greater than that of Y-liangyou 900（average decrease of 2.27%in two years）.2.Changes in nitrogen use efficiency of low-nitrogen tolerant rice varietiesUnder low nitrogen conditions,the nitrogen accumulation of Deyou 4727 was not significantly different from that of Y-liangyou 900,but its nitrogen internal utilization efficiency,nitrogen harvest index and nitrogen recovery use efficiency were higher than those of Y-liangyou 900.From 0 kg N hm^-2to 240 kg N hm^-2,the growth rate of aboveground nitrogen accumulation in Deyou 4727 was 149.23%and 129.23%in 2020 and 2021,respectively,and Y-liangyou 900 was 117.94%and 83.90%,respectively,the growth rate of Deyou 4727 was higher than that of Y-liangyou 900;nitrogen internal utilization efficiency decreased with the increase of nitrogen fertilizer application,Deyou 4727 decreased by 39.76%and 50.31%in2020 and 2021,respectively,while Y-liangyou 900 decreased by 29.35%and 22.85%in two years.Nitrogen recovery use efficiency of Deyou 4727 decreased slightly with the increase of nitrogen application rate,the two years decreased by 5.61%and 8.33%respectively.In conclusion,the low-nitrogen tolerant rice varieties have the characteristics of high yield and nitrogen use efficiency under low nitrogen conditions;Increased nitrogen fertilization has little effect on yield increases in low-nitrogen tolerant varieties,but will lead to a decrease in nitrogen use efficiency.