Effects Of Planting Density And N Application On The Yield And N Fertilizer Use Efficiency Of Summer Maize In Guanzhong Area

To investigate the effects of different planting densities and nitrogen application on the growth and development of summer maize,this study was conducted in 2021 and 2022at the Cao Xinzhuang Experimental Farm of Northwest Agriculture and Forestry University and the Key Laboratory of Crop Physiology,Ecology and Farming on the Loess Plateau of Northwest China under the Ministry of Agriculture and Rural Affairs.Two-factor split zone experimental design was used and the high-yield summer maize variety Zhengdan 958 was selected as the experimental material.Two planting densities of67500（LD）and 97500（HD）plants·hm^-2and five nitrogen levels of 0（N0）,135（N1）,180（N2）,225（N3）and 270（N4）kg N hm^-2were set.The study investigated the effects of different N application rates on summer maize yield,agronomic traits,photosynthetic characteristics,grain filling characteristics,plant nutrient uptake and N fertilizer utilization at two planting densities,and comprehensively evaluated the effects of planting density and different N fertilizer application rates on the growth and yield of summer maize,with a view to providing theoretical basis and technical support for high-yield and efficient summer maize cultivation in the Guanzhong Plain.The main research results are as follows:（1）Planting density and N application had a significant effect on summer maize yield and NUE（N fertiliser utilisation）.Increasing planting density reduced the thickness of the ears,the number of ears and the weight of 100 grains of summer maize,while the seed yield increased significantly,with an average increase of 19.8%to 21.61%at higher densities compared to lower densities at all levels of N application.Compared with no N treatment N0,the ears length,ears thickness,ears grain number,100 grain weight and yield of summer maize were significantly increased under N application treatment,with the seed yield showing N4>N3>N2>N1.Among them,the difference of seed yield between N3 and N4 treatments was not significant.Seed yield was 13,091.54 kg·hm^-2and 14,491.81kg·hm^-2under HDN3 treatment in both years,while total plant nitrogen accumulation was also highest at 344.16 kg·hm^-2and 348.69 kg·hm^-2,respectively.Under high density cropping conditions,NUE at different N application levels showed N3>N4>N2>N1,reaching the highest at 49.23%and 53.64%under HDN3 treatment respectively.In summary,increasing the planting density to 97,500 plants·hm^-2and appropriately reducing the N fertilizer application to 225 kg·hm^-2can achieve a synergistic increase in summer maize yield and NUE,which is a suitable planting pattern in this region.（2）Increasing planting density resulted in a significant increase in summer maize plant height and leaf area index,while stalk thickness and dry matter accumulation per plant decreased significantly.Summer maize plant height,stalk thickness,leaf area index and dry matter accumulation were all significantly higher in the nitrogen application treatment than in the non-application treatment.The leaf area index of summer maize in both years was highest under the HDN3 treatment,at 5.29 and 5.66 respectively,an increase of 19.60%and 10.28%compared to HDN0 treatment and an increase of 14.57%and 15.35%compared to the LDN3 treatment.Dry matter accumulation per plant at maturity was highest in both seasons under LDN4 treatment,at 353.8 g and 339.6 g.Under high density conditions,dry matter accumulation at different N levels was N3>N4>N2>N1>N0,with HDN3 increasing by 19.75%to 24.90%compared to HDN0.In summary,the application of 225 kg·hm^-2of pure N under dense planting conditions maintained a high green leaf area in the middle and late stages of grain filling,which significantly increased the dry matter accumulation of the plant at maturity and facilitated the formation of grain yield.（3）The SPAD and net photosynthetic rate（Pn）of spike position leaves were significantly lower in dense summer maize compared to conventional planting density.The SPAD and Pn were significantly higher in the N treatment than in the non-N treatment（P<0.05）.The net photosynthetic rate of summer maize at tassel stage in both years was the best under HDN3 treatment,with a significant increase of 20.72%and 13.95%compared to HDN0（P<0.05）,but not significantly different from HDN4（P>0.05）.In conclusion,it is suggested that under high density conditions,appropriate reduction of nitrogen fertilizer（N3）can maintain a longer duration of high SPAD and Pn values in spike leaves,which is conducive to the accumulation of photosynthetic products.（4）The 100 kernel weight of densely planted maize was significantly lower than that of conventional planting density.The 100 kernel weight was significantly greater in the nitrogen treatment than in the non-nitrogen treatment.Under low density conditions,the maximum filling rate of the treatments with different levels of nitrogen application showed N4>N3>N2>N1>N0;under high density conditions,it showed N3>N4>N2>N1>N0,with the maximum filling rate reaching a maximum of 1.48 g·d^-1and 1.32 g·d^-1under the HDN3treatment,respectively.The time to maximum grouting rate(T_max),the growth at maximum grouting rate(W_max),the maximum grouting rate(G_max)and the active grouting period（D）all decreased with increasing density.Under low density conditions,both W_maxand G_maxincreased continuously with increasing N application.Under high density conditions,HDN3 treatment increased G_maxby 18.29%and 19.31%,W_maxby 19.49%and 23.12%compared to HDN0.HDN3 treatment significantly promoted the seed filling process and laid a solid foundation for grain weight increase.In conclusion,increasing planting density(97,500 plants·hm^-2)and reducing N fertilizer input(225 kg·hm^-2)can significantly improve leaf photosynthesis of summer maize,promote its grain filling process,increase the number of ears and grain weight,and ultimately obtain higher summer maize grain yield and N fertilizer utilization.Therefore,a planting density of 97,500 plants·hm^-2with 225 kg·hm^-2of N fertiliser is the best production model for improving summer maize yields and N fertiliser utilisation in this area.