Effect Of Low Nitrogen Rate Combined With High Plant Density On Growth And Grain Yield In Machine-transplanted Double-cropping Rice

There are some problems in rice cultivation with high nitrogen rate and sparse planting,such as high input,unstable yield and low nitrogen use efficiency,while the cultivation method of low nitrogen rate combined with high plant density has the advantages of taking into account yield and nitrogen use efficiency and saving fertilizer expenditure.In order to find out the effects of low nitrogen rate combined with high plant density on growth and grain yield in machine-transplanted double-cropping rice,and then to provide theoretical basis for popularizing the cultivation model of low nitrogen rate combined with high plant density.Therefore,under the field experiment condition,taking hybrid rice Zhuliangyou 819 and conventional rice Zhongjiazao 17 as the early rice materials,hybrid rice Taiyou 390 and conventional rice Xiangwanxian 13 as the late rice materials with four nitrogen fertilizer and density levels were studied.Zero-N with conventional density(0 kg N/ha,285700 holes/ha),zero-N with high density(0 kg N/ha,363600 holes/ha),low N rate with high density(120 kg N/ha,363000 holes/ha),conventional N rate with conventional density(150 kg N/ha,285700 holes/ha)were set up using split panel design.The tiller dynamics,dry matter content,leaf area index,yield and its components,chlorophyll relative content(SPAD value),photosynthetic characteristics and population canopy structure parameters of early and late rice were measured,and the rate of productive tillers,growth rate of population,photosynthetic potential and nitrogen use efficiency were calculated.The results were as follows:1.Compared to conventional treatments,under the treatment of low N rate with high density treatment,the individual dry matter weight of the early and late rice was decreased,but the population indexes such as the number of tillers per unit area,the dry matter weight of population,the phase accumulation of dry matter,the population growth rate,the harvest index,the leaf area index and the photosynthetic potential in post-panicle were unchanged or increased.2.Compared to conventional treatments,the change of grain number per spike,seed setting rate and 1000-grain weight under low N rate with high density treatment was not significantly,but the number of effective panicles had varied greatly.Maintaining higher number of effective panicles was a key condition to ensure the yield of early and late rice under low N rate with high density conditions.The effective panicles number of Taiyou390 and Xiangxian13 increased,and the effective panicles number of Zhongjiazao 17 did not decrease,so the yield of the three varieties did not decrease either,which were 9.01,8.77 and 7.53t/hm~2,respectively;while the yileds under conventional treatment were 9.54,8.77 and 7.72t/hm~2,respectively.The effective panicles number of Zhuliangyou 819 had decreased greatly,and its yield decreased obviously,which was 7.23t/hm~2,while the yield was 8.19t/hm~2 under conventional treatment.3.Compared to conventional treatments,the nitrogen partial factor productivity(NPFP)of the early and late rice increased under the treatment of low N rate with high density,and the nitrogen agronomic efficiency(NAE)and the nitrogen recovery efficiency(NRE)of Zhuliangyou819?Zhongjiazao17 and Xiangwanxian 13 increased to varying degree.While the NAE and the NRE of Taiyou390 decreased,but not significantly,this is mainly due to the higher yield of non-nitrogen treatment cause the error of NAE and NRE calculated by the difference method.4.Compared to conventional treatments,there were no significant changes in SPAD value,net photosynthetic rate and characteristics of canopy structure of Zhuliangyou 819,Zhongjiazao 17and Xianglaoxian 13 under low N rate with high density treatment after heading stage.The SPAD value at 15 days after heading stage and the net photosynthetic rate at heading stage of Taiyou 390decreased significantly,and DIFN increased significantly at 15 days after heading,but there was no significant change in the other characteristics of population canopy structure after heading stage.5.Considering the performance of the population growth status,the yield and its components,the nitrogen utilization efficiency and the photosynthetic utilization ability of machine-transplanted double-cropping rice,under the condition of nitrogen-decreasing and density-increasing,apart from Zhuliangyou 891,Zhongjiazao 17,Taiyou 390 and Xiangwanxian 13 could still guarantee the original yield.The results showed that the population effect of densification could make up for the adverse effects of nitrogen reduction on rice growth and yield in this experiment which nitrogen rate reduction 20%with planting density increase 27.27%.Moreover,the nitrogen utilization efficiency also improved.Therefore,the cultivation pattern of low nitrogen rate combined with high density is worth popularizing,but should pay attention to choosing suitable crop variety and time effect.6.Under the condition of low nitrogen rate combined with high plant density in this experiment,the adaptability of Zhongjiazao 17 and Xiangwanxian 13 was higher than those of Taiyou 390 and Zhuliangyou 819,so the suitability of conventional rice was better than those of hybrid rice.