Effects Of Nitrogen Fertilizer And Plant Density Interaction On Tillering Formation,canopy Light And Nitrogen Distribution,and Grain Yield Of Rice

Rice（Oryza sativa L.）is one of the most important food crops in China and even the world,playing an important role in ensuring food security.In recent years,the expansion of cities and towns has led to a continuous increase in construction land,resulting in a decline in cultivated land.Enhancing rice yield per unit area has become a key measure to effectively increase rice production.Fertilizer and density play crucial roles in regulating rice population structure and influencing rice yield.Studies have revealed that reasonable and dense planting of small plants can improve land use efficiency and light energy use efficiency per unit area.It is an important technical measure for stable and high yield,but it is time-consuming and labor-intensive.Applying nitrogen fertilizer can significantly promote rice tillering,increase population size,and achieve a dense planting effect.However,increasing the long-term application of nitrogen fertilizer to enhance rice yield not only raises production costs but also causes a series of environmental quality problems due to excessive or unreasonable use.Machine transplanting saves labor and time while further increasing transplanting density.Clarifying the interaction effect between nitrogen fertilizer and density on increasing yield and stability of rice under the background of fertilizer reduction and efficiency enhancement is of great significance.This paper studied the effects of nitrogen density interaction on rice tillering formation,canopy light and nitrogen distribution,yield,and nitrogen fertilizer use efficiency through a 2-year field experiment.It aims to provide a theoretical basis for rational fertilization and cultivation of rice.The main research findings are as follows:（1）The nitrogen content in the main stem and leaves significantly affected the formation of rice tillers.When the nitrogen application rate was 270～360 kg/hm² and the density was 315000 holes/hm²,the maximum effective number of tillers could be obtained,ranging from 3.2～3.6×10⁶/hm².When the nitrogen content in the main stem reached 1.8%and the nitrogen content in the leaves reached 2.7%,the rice plant began to tiller.When the nitrogen content in the main stem reached 3.8%and the nitrogen concentration in the leaves reached 5.4%,the plant entered rapid tillering.The number of stems and tillers showed a trend of first increasing and then decreasing with the growth process,and reached the maximum tillering around 30 days after transplanting.Nitrogen and plant density interaction significantly affected the effective tiller number.The reasonable nitrogen and plant density allocation treatments in 2021 and 2022 were both 270 kg/hm² of nitrogen application and 270000 holes/hm² of density,with effective tiller numbers of 2.9×10⁶/hm²and 2.8×10⁶/hm²,respectively.（2）Nitrogen and plant density interaction regulated the photosynthesis and nitrogen distribution in rice canopy by changing the photosynthetic effective radiation,leaf area index,and specific leaf nitrogen in the middle and upper parts of the canopy（40～100 cm above the ground）at flowering stage.Compared with the high nitrogen and high density（N_HD_H）treatment,the reasonable nitrogen and plant density allocation（N_MD_M）treatment increased the average photosynthetic effective radiation of the upper and middle parts of the rice canopy by 11.2%during the flowering period.For every 1 cm increase in canopy height,the average increase rate of leaf nitrogen increased by 80.0%.Compared with low nitrogen and low density（N_LD_L）treatment,N_MD_M treatment increased the upper leaf area index by 65.5%.The canopy treated with N_MD_M had both lower upper extinction coefficient and higher nitrogen reduction coefficient.The effective radiation of the upper and middle photosynthetic canopy drived a higher specific leaf nitrogen distribution,and the value of the light nitrogen matching coefficient was close to the ideal value.（3）Reasonable nitrogen and plant density allocation treatment(N₂₇₀D_27.0)significantly improved rice yield and nitrogen fertilizer use efficiency.In terms of yield,compared with the no nitrogen application（N₀）treatment,the yield of each nitrogen application treatment in the Shayang and Jingzhou experimental sites increased by an average of 973 kg/hm² and2901 kg/hm²,with an increase of 11.3%and 38.3%,respectively;Compared with the low density(D_18.0)treatment,the yield of each densification treatment at the two experimental sites increased by an average of 772 kg/hm² and 651 kg/hm²,with an increase of 8.8%and6.9%,respectively.When the nitrogen application rate was 270 kg/hm² and the density was270000 holes/hm²,the yield of the experimental sites in Shayang and Jingzhou reached its maximum,reaching 11860 kg/hm² and 12747 kg/hm²,respectively.In terms of nitrogen fertilizer use efficiency,compared with D_18.0 treatment,nitrogen use efficiency for biomass produciton（NUEb）of each densification treatment in the Shayang experimental site increased by an average of 10.1 kg/kg,with an increase of 8.7%;The average increase in nitrogen recovery efficiency（NRE）was 11.0%,with an increase of 23.2%;The average increase in NUEb at each densification treatment point in Jingzhou was 11.1 kg/kg,with an increase of 12.3%;The average increase in NRE was 8.6%,with a growth rate of 17.8%.When the nitrogen application rate was the same,optimizing density significantly improved the nitrogen use efficiency.Compared with the N₂₇₀D_18.0 treatment,the reasonable nitrogen and density allocation(N₂₇₀D_27.0)treatment in the Shayang experimental site increased NUEb and NRE by 8.0%and 25.2%,respectively;in Jingzhou increased by 10.8%and15.1%respectively.（4）Design a nitrogen control model based on the target yield,when the density was27000～28000 holes/hm² and the nitrogen application rate was 240～280 kg/hm²,the target yield of 10500～12000 kg/hm² could be achieved.The yield components were:Panicles of310～325/m²,spikelets of 210～230,and filled grain rates of about 88%.The maximum number of tillers during the tillering stage needed to reach 5.6～6.6×10⁶/hm²,effective tillers obtained at the end of tillering 3.1～3.5×10⁶/hm².In summary,a reasonable nitrogen and density configuration treatment regulated the effective tiller number of rice by adjusting the nitrogen content in the main stem and leaves,improved the light and nitrogen distribution characteristics of rice canopy to promote the degree of light and nitrogen matching in the canopy,and thereby improved yield and nitrogen fertilizer use efficiency.