Effects Of Nitrogen Fertilizer On Anti-aging Properties Of Leaves And Yield Of Maize In Rainfed Regions

In order to explore the suitable nitrogen fertilizer application program for spring maize in the dry farming area of Gansu,this experiment is based on the nitrogen fertilizer operation positioning experiment set by Gansu Agricultural University Dryland Agricultural Comprehensive Experimental Station in 2012,and studied four nitrogen application levels(N0:no nitrogen fertilizer,N1:nitrogen application 100 kg·hm^-2,N2:nitrogen application 200 kg·hm^-2,N3:nitrogen application 300 kg·hm^-2)and two top dressing periods and distribution ratio（T1:1/3 base fertilizer+2/3 top dressing at jointing stage,T2:1/3 base fertilizer+1/3 top dressing at the jointing stage+1/3 top dressing at the belling stage）on maize grain yield and water and nitrogen use efficiency,The main mechanism of nitrogen fertilizer management affecting maize grain yield and water and nitrogen use efficiency was discussed from the perspective of maize growth and development and leaf anti-senescence characteristics.The main results are as follows:1.Appropriate nitrogen fertilizer application can significantly increase maize yield,water and nitrogen use efficiency.The grain yield and water use efficiency of maize increased with the increase in nitrogen application rate.The grain yield of maize under N1,N2,and N3 levels increased by94.14%,170.99%,and 189.13%,respectively,compared with N0.The water use efficiency of these three compared with N0,it increased by 79.31%,140.85%,and 160.81%respectively.However,the grain yield and water use efficiency of maize were not significantly different under N2 and N3 levels.The highest grain yield and corresponding nitrogen application rate fitted by the equation are close to the N3 level.The partial productivity of nitrogen fertilizer and the agronomic efficiency of nitrogen fertilizer decreased with the increase of fertilization level.The partial productivity of nitrogen fertilizer and the agronomic efficiency of nitrogen fertilizer under N2 level were increased by 40.58%and 35.60%respectively compared with N3 level.Fertilization period and distribution ratio had no significant effect on the above indicators.2.Nitrogen application promotes the growth and development of maize.Each nitrogen application level significantly increased the plant height,leaf area index and dry matter accumulation of maize,but when the nitrogen application rate exceeded 200 kg·hm^-2,the above indicators no longer increased significantly.The nitrogen application period and distribution ratio had no significant effect on the growth and development of maize.3.Nitrogen application improves the anti-aging performance and drought resistance of maize leaves.Anti-aging protection enzymes SOD（superoxide dismutase）,POD（peroxidase）and CAT（catalase）activities and MDA（malondialdehyde）,soluble protein content all increased with the increase of nitrogen application;The comprehensive score of the anti-aging protective enzyme system at the N3 level was increased by 200.00%compared with the N2 level;The fertilization period and the distribution ratio had no significant effect on the above indicators.During water deficit,the soluble sugar content increases with the increase of nitrogen application rate,and the drought resistance of maize is enhanced.When water is sufficient,the soluble sugar content is mainly affected by nitrogen stress,and with the increase of nitrogen application rate shows a decreasing trend.4.Nitrogen application promotes the photosynthesis of maize.Maize leaf chlorophyll content,net photosynthetic rate,transpiration rate,stomatal conductance,PEPC（phosphoenolpyruvate carboxylase）,Rubisco（ribulose-1,5-bisphosphate carboxylase）and PPDK（pyruvate phosphate dikinase）activity increased with the increase of nitrogen application level.The average net photosynthetic rate of maize under N1,N2,and N3 levels increased by 74.23%,128.22%,and158.90%,respectively,compared with N0.The comprehensive score of photosynthetic characteristics at N3 level was 50.00%higher than that at N2 level.5.Maize grain yield was positively correlated with the comprehensive factors of anti-aging protective enzyme system（0.912**）and photosynthetic characteristics（0.971**）;Maize grain yield was negatively correlated with nitrogen partial productivity（-0.725**）and nitrogen agronomic efficiency（-0.278）.In summary,reasonable nitrogen fertilizer management can enhance the drought resistance of maize.At the same time,reasonable nitrogen application can increase the anti-aging protective enzyme activity and soluble protein content of leaves,enhance the anti-aging ability of maize,and increase the chlorophyll content,key photosynthetic enzyme activity and net photosynthetic rate of maize leaves,promote the accumulation and transportation of dry matter in the late growth period,thereby improving maize grain yield,water use efficiency and nitrogen fertilizer use efficiency,and promote sustainable maize production.Considering the yield and water and nitrogen use efficiency,it is recommended to apply 200 kg·hm^-2 of nitrogen to spring maize in the dry farming area of Gansu,and apply at 1/3 base fertilizer+2/3 jointing stage.