Coupling Effect Of Nitrogen Rate And Planting Density On Growth Of Drip-irrigated Spring Maize In The Hexi Region

The reduction of arable land and low nitrogen use efficiency are two restrictive factors for agricultural development in China.Optimizing nitrogen application rate and planting density is an important measure to promote crop yield and agricultural sustainable development.In this study,spring maize integrated with drip irrigation and water and fertilizer in Hexi area was taken as the research object to study the effects of planting density（D1:80,000/ha,D2:100,000/ha,D3:120,000/ha）and nitrogen application rate（N240:240kg N/ha,N180:180 kg N/ha,N0:0 kg N/ha）on the growth,physiological indexes,canopy structure,grain filling process,leaf senescence process,yield,water and nitrogen utilization efficiency and economic benefits of two spring maize（QS51:Qiangsheng 51,ZD958:Zhengdan 958）.The main conclusions are as follows:（1）The effects of N rate and planting density on the growth and yield of drip irrigated spring maize were clarifiedUnder medium and high planting density,leaf area index had obvious advantages,while plant height and stem diameter decreased with the increase of planting density.There was a significant correlation between aboveground dry matter accumulation and yield,and both of them reached the maximum under medium density planting.Excessive nitrogen application at high density is beneficial to maize growth,while appropriate nitrogen application at low density has more advantages in promoting maize growth.With the increase of planting density,the yield first increased and then decreased;with the increase of nitrogen application rate,the yield gradually increased under high planting density,while the yield of N240 and N180 had no significant difference under low planting density.Both varieties obtained the highest yield（13141 kg/ha and 17644 kg/ha）under D2N180 treatment,but the yield difference of ZD958 under D2N240 and D2N180 treatment was not significant.（2）The effects of N rate and planting density on canopy structure and light interception were revealedWith the increase of planting density,the leaf length and leaf width of different canopy of the two varieties decreased,and the leaf direction increased first and then decreased.With the increase of nitrogen application rate,leaf length and leaf width increased,leaf direction showed the same trend,and were the largest in N180 treatment,indicating that suitable planting density and nitrogen application rate can shape good canopy structure,so as to optimize the light distribution.Nitrogen application significantly reduced the light transmittance of ear layer,and the light transmittance of ear layer decreased first and then increased with the planting density.Both of them had no significant effect on the light transmittance of bottom layer.（3）The effects of N rate and planting density on the physiological indicators and two important physiological processes（leaf senescence and grain filling process）of maize were investigated.The leaf senescence process of maize can be simulated by Logistic equation.Nitrogen application reduced leaf senescence start time,average leaf senescence rate and maximum leaf senescence rate,but there was no significant difference between N240 and N180 under D1 and D2.The leaf senescence start time and average leaf senescence rate increased linearly with the increase of planting density,but the growth ratio was different under different nitrogen application rates.Grain filling process can be accurately described by deterministic equations.With the increase of planting density,the maximum filling rate and average filling rate increased and then decreased.Nitrogen application had significant effect on grain filling characteristic parameters,but there was no significant difference between N240 and N180.（4）The effects of N rate and planting density on water and N utilization efficiency and economic efficiency were elucidated.Under D1 treatment,the water use efficiency of the two varieties increased first and then decreased with the increase of nitrogen application rate,and reached the peak at N180,which was significantly higher than that of N240（QS51 increased by 15.0%,ZD958increased by 7.8%）;water use efficiency under D2 and D3 treatments increased with the increase of nitrogen application rate.Nitrogen use efficiency,nitrogen partial factor productivity and nitrogen agronomy efficiency increased first and then decreased in a certain planting density range,and reached the peak under D2 planting density.When the nitrogen fertilizer amount was 180 kg N ha^-1,the nitrogen use efficiency was the highest.Under the same planting density,nitrogen use efficiency and nitrogen partial productivity decreased with the increase of nitrogen application rate.Both varieties obtained the maximum net income（12096 CNY/ha and 13955 CNY/ha）under D2N180 treatment.Compared with D3N240,the nitrogen application rate decreased by 33.3%,but the net income increased by1561 CNY/ha（QS51）and CNY/ha,respectively.（5）Suitable combination of planting density and nitrogen rate of spring maize and their thresholds were put forwardBased on the principal component analysis,maize physiology,water-nitrogen use efficiency,yield and economic benefits were comprehensively analyzed.The results showed that D2N180 treatment ranked first,followed by D2N240 and D3N240 treatments,indicating that 100000 plants/ha and 180 kg N/ha were suitable for local spring maize planting density and nitrogen application.Based on the binary quadratic regression and normalization method,it was found that when the nitrogen application rate was 110～190kg N/ha and the planting density was 93500～115500/ha,the comprehensive benefits of water use efficiency,yield and economic benefit of spring maize could reach 95%of their respective maximum values.