Effects Of Straw Returning And Nitrogen Management On Nitrogen Accumulation And Photosynthetic Performance Of Spring Maize

Maize is an important grain and forage crop,maize cultivation is important for food security,and at the same time a large amount of straw will be produced.Straw returning is the most direct way to solve the waste of straw resources.Straw returning can supplement nutrients to soil,but change soil nitrogen supply characteristics.The supply of nitrogen fertilizer directly affects the growth and yield of crops.Photosynthesis is an important physiological process of crop growth and yield formation,straw returning and nitrogen management have important effects on photosynthetic performance of maize.To study the effects of straw returning and nitrogen fertilization on nitrogen uptake and photosynthetic performance of maize,a frame culture and continuous positioning experiment was started in 2016,which will provide theoretical basis and reference for scientific nitrogen application and maize straw returning.A three-factor split-plot design was adopted in this experiment,the main plot was straw returning method with no straw returning（S₀）and straw returning（S₁）,which the amount of straw returning was 0,12 t·ha^-1,and the sub-plot was nitrogen application with 0（N₀）,175（N₁）,350（N₂）kg·ha^-1,which was applied with ¹⁵N labeled urea,the nitrogen content of urea was 46%,and each fertilizer application amount set two application methods,one ratio of base fertilizer and top dressing applied was 1:1(N_1-1、N_2-1),the other ratio of base fertilizer and top dressing applied was 1:0(N_1-0、N_2-0),the urea amount of 350 kg·ha^-1was common application in local agricultural production.The results showed that:Straw returning and nitrogen fertilization had significant effects on nitrogen accumulation of maize.The nitrogen accumulation in the treatment of no straw returning（S₀）was higher than that in the straw returning（S₁）significantly in stalk of maize at three-leaf and jointing stages.The nitrogen accumulation in S₁was higher than that in S₀at maturity stage.About the nitrogen accumulation at maturity stage of maize,the treatment of two equal amount of fertilizer was significantly higher than that in one-time fertilizer.Straw returning was not beneficial to nitrogen accumulation in the early growth of maize,but beneficial to the late growth stage of maize.Straw returning and nitrogen fertilization had significant effects on nitrogen use efficiency of maize.Straw returning had significantly negative correlation with nitrogen use efficiency of maize.Nitrogen application and base-to-chase ratio had positive correlation with nitrogen use efficiency of maize.Nitrogen use efficiency in two equal amounts of fertilizer was significantly higher than that in one-time fertilizer.Compared with 350 kg·ha^-1urea used in local agriculture,half application of nitrogen fertilizer was not conducive to the improvement of nitrogen uptake efficiency in maize.Straw returning and nitrogen fertilization had significant effects on available nitrogen content in the soil.The content of available nitrogen in soil before sowing was higher than that after harvest.Straw returning had no significant effect on soil available nitrogen content.In S₁and S₁treatment,the content of soil available nitrogen in nitrogen application treatments was significantly higher than that in N_0-0treatment.The content of soil available nitrogen in base-topdressing ratio 1:0 was significantly higher than that in base-topdressing ratio 1:1 under N₂application.Appropriate proportion of nitrogen fertilizer was more beneficial to the absorption and utilization of soil available nitrogen by maize.At the urea application rate of 350 kg·ha^-1,the content of relative chlorophyll in maize at jointing,tasseting and filling stages with the treatment of two equal amounts of fertilizer was significantly higher than that in one-time fertilizer,but there was no significant difference at maturity stage.Compared with N_0-0treatment,Fv/Fm and Phi2 showed an increasing trend after nitrogen application.The activity of PSⅡreaction center was enhanced by nitrogen application,and the photochemical quantum yield and photochemical efficiency were improved.Under the common nitrogen application rate of 350 kg·ha^-1,the Phi2 reached the maximum at grain filling stage and maturity stage.Straw returning and nitrogen fertilization had significant effects on maize yield.The yield of S₁treatment was significantly higher than that of S₀.Compared with one-time nitrogen application,two equal nitrogen application significantly increased maize yield.In the S₁and S₀treatment,the maize yield of the base-topdressing ratio 1:1 treatment significantly increased by2.94%and 6.02%compared with that in base-topdressing ratio 1:0 under N₁nitrogen.In the S₁and S₀treatment,the maize yield of the base-topdressing ratio 1:1 treatment significantly increased by 6.20%and 2.72%compared with that in base-topdressing ratio 1:0 under N₂nitrogen.The highest yield of maize was 269.05 g/plant in the treatment of straw returning and topdressing with common urea application amount(350 kg·ha^-1)in local agriculture.