| Hebei Province is an important corn producing area in China,and its corn planting area and total yield account for 8.26%and 7.67%of the whole country respectively.The high and stable yield of corn in this region is of great practical significance to ensure the food and food safety in China.At present,the excessive application of nitrogen fertilizer in maize production in this region leads to the increasing imbalance of soil nutrition,low fertilizer use effciency leads to groundwater pollution and excessive emission of harmful gases,and causes a series of environmental protection problems.Therefore,field experiments were set up in Mazhuang experimental station of Hebei Agricultural University in Xinji City,aiming at the problems of unreasonable nitrogen application and low fertilizer utilization of maize in the low plain area of Hebei Province,taking nitrogen management mode and varieties as breakthrough points,with Xianyu 688(XY688)and Jifeng 2(JF2)were used as experimental materials.The purpose of this study was to provide scientific basis for determining the optimal proportion of conventional urea and slow-release nitrogen fertilizer,reducing the amount of nitrogen fertilizer,improving nitrogen use efficiency of summer maize,and providing theoretical support for genetic breeding and optimizing nitrogen management of nitrogen efficient maize Varieties in Hebei Province.The main results are as follows:(1)There were significant differences in yield and nitrogen use efficiency between the two maize genotypes.Compared with JF2,XY688 showed higher nitrogen transport capacity and efficiency in vegetative organs,increased dry matter assimilation after anthesis,accumulated more dry matter in mature stage,obtained higher grain yield and nitrogen use efficiency,and significantly improved grain yield.The grain yield of XY688 increased by 6.92%and 18.27%compared with JF2 in 2019 and 2020,respectively.Among them,the number of grains per spike was the main factor to increase yield,and XY688 had obvious advantages in nitrogen absorption and utilization efficiency.(2)There were significant differences in leaf nitrogen metabolism physiology between the two maize genotypes.Compared with JF2,XY688 showed higher leaf NR activity,increased activities of key enzymes of nitrogen metabolism such as GS,GOGAT,Got and GDH,and increased contents of endogenous hormones such as IAA and GA.at flowering and maturity,the average leaf area index of XY688 was 22.79%and 19.32%higher than JF2,respectively Compared with JF2,the average leaf photosynthetic rate increased by 12.64%and 17.41%respectively,which ensured that maize could accumulate more photosynthetic products after anthesis.Compared with JF2,the average IAA content of XY688 was 10.89%higher than that of JF,and the average GA content of XY688 was 5.63%higher than that of JF.Compared with JF2,the average leaf area index of XY688 increased by 9.13%and 20.93%at flowering stage and maturity stage,and the average leaf photosynthetic rate of XY688 increased by 9.41%and 16.84%respectively.(3)Polyaspartic acid chelating nitrogen fertilizer(PASPN)increased maize yield and nitrogen utilization efficiency.The treatment of PASPN can guarantee the nutrient demand of the high-efficiency nitrogen variety XY688,improve the nitrogen utilization efficiency,and increase the accumulation of dry matter and nitrogen in the upper part of the ground.Compared with FT and opt,the yield of XY688 was significantly increased under PASPN treatment,and the average grain yield of XY688 increased by 11.21%and 21.83%respectively in two years compared with FT and opt treatment.(4)Polyaspartic acid chelating nitrogen fertilizer(PASPN)effects the activities of nitrogen metabolism enzymes and gene expression in leaves after anthesis.Paspn treatment increased the activities of GS,GOGAT,got and GDH,decreased NR activity,increased IAA and GA contents,and increased leaf area index and photosynthetic rate.After PASP treatment,the relative gene expressions of ZmNR、ZmGAGOT、ZmAspAT and Zmgs1.1,ZmGSl.1、ZmGS1.2、ZmGS1.3、ZmGS1.4 and ZmGS were up-regulated,but the expression of JF2 related genes was less affected.(5)Combined application of conventional urea and slow-release urea could regulate nitrogen metabolism and endogenous hormone balance in maize leaves after anthesis.Combined application of conventional urea and slow release urea(US7)significantly increased the activities of key enzymes of nitrogen metabolism such as NR,GS,GOGAT,got and GDH,increased the contents of endogenous hormones such as IAA and GA,increased leaf area index and photosynthetic rate,and ensured that maize could accumulate more photosynthetic products after anthesis.(6)The mixture of conventional urea and slow release urea can reduce the cost of fertilizer application,realize the continuous relay of nutrient supply between fertilizers,and give full play to the efficiency of controlled release urea.The optimum ratio of conventional urea and slow release urea was 3:7(US7)in summer maize in Hebei plain.In summary,this study has systematically dissected the plant growth and development traits,N uptake and assimilation properties,physiological parameters,expression patterns of corresponding genes,and the yield traits.The characteristics of nitrogen distribution and transport and nitrogen metabolism in leaves after flower were clarified under different ratio of urea and slow release urea.For the first time,the optimum ratio of urea and slow release urea in summer maize production in Taihang mountain plain area was 3:7(US7),namely conventional urea(54 kg/hm-2)+slow release urea(126 kg/hm-2).In the plain area of Taihang Mountain of Hebei Province,the optimal proportion of urea and slow release urea was clarified for the first time.The response mechanism of nitrogen assimilation and metabolism characteristics of XY688 to PASP in high efficiency maize variety was studied,which enriched the Research Report on the effect of PASP combined with urea in summer maize production in this region.Our results provide the effective N fertilizer management for Taihangshan plain in Hebei province and the scientific basis to elevate yield formation capacity and plant NUE in summer maize. |
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