| The loss of nitrogen nutrients in farmland is one of the main sources of non-point source pollution in China.In the early stage,in order to achieve high yield,a large amount of nitrogen fertilizer was invested in farmland,and the serious loss of nitrogen has affected the development of agricultural intensification in China.Controlling nutrient input and improving nitrogen use efficiency are important measures to solve non-point source pollution.Maize,as the main grain crop in China,needs more nitrogen fertilizer.Foliar fertilizer absorption is faster,strong operability,and can reduce the damage to soil quality.In this study,maize Zhengdan 958 was used as the experimental material,and the effects of foliar urea spraying on maize seedling physiology and biochemistry and its mechanism were studied through the laboratory simulation experiment of nutrient solution culture.The main test results are as follows:(1)Effects of foliar spraying urea on nitrogen uptake and utilization and physiological and biochemical characteristics of maize seedlings under low nitrogen stress.Under low nitrogen stress,spraying urea increased the relative chlorophyll content(SPAD)of old leaves of maize,slowed down the senescence of mature leaves of maize plants,spraying urea with 10% concentration significantly decreased the root-shoot ratio of maize,and promoted the absorption of nutrients in the shoot of maize.Spraying urea with 10% concentration could effectively increase nitrogen concentration in different parts of the plant and nitrogen accumulation in the shoot.Compared with spraying pure water,nitrogen concentration in maize leaves,stems and roots increased by 48.35%,21.54% and 14.45%,respectively,while nitrogen content in the shoot increased by 27.92%.At the same time,urea spraying significantly reduced K accumulation in maize roots,but increased Zn concentration in maize roots.The aboveground moisture content of maize under low nitrogen stress decreased by 37.94% compared with that of normal maize.The moisture content of the upper part of the corn field was increased by35.09% by spraying 5% urea compared with spraying pure water.(2)Effects of foliar spraying urea and N-(n-Butyl)thiophosphoric triamide(NBPT)on nitrogen uptake and utilization and physiological and biochemical characteristics of maize at seedling stage.Spraying 5% urea increased the SPAD value of maize leaves,but the SPAD value of maize leaves decreased significantly after applying NBPT.Spraying 5% urea reduced the fresh weight of lower leaves,while spraying NBPT alone reduced the fresh weight of the first lower leaf.The addition of NBPT significantly increased the fresh weight of the second lower leaf of corn sprayed with 2% urea.The increase of NBPT significantly increased the stem fresh weight of corn sprayed with 2%urea.However,increasing NBPT decreased the root fresh weight of corn without urea spraying,and significantly increased the root fresh weight of corn with 2% urea spraying.Overall,increasing NBPT increased shoot and plant total fresh weight of maize sprayed with 2% urea.Spraying 5% urea increased aboveground nitrogen concentration.Increasing NBPT had no significant effect on aboveground nitrogen concentration.The root nitrogen concentration of corn sprayed with 2% and 5%urea was significantly decreased by 4.37% and 1.42% after adding NBPT.The chlorophyll content of maize leaves decreased slightly with the increase of NBPT,but the difference was not significant.(3)Effects of foliar spraying urea on nitrogen uptake and utilization and physiological and biochemical characteristics of maize at seedling stage.With the increase of urea concentration,plant height,leaf area,aboveground biomass,root morphology(total root length and number of root tips)and aboveground nitrogen uptake of the plant all showed promoting effects at low concentrations and inhibiting effects at high concentrations.In addition,spraying 2% urea significantly increased the height and leaf area,aboveground biomass,total root length,root tip number and aboveground nitrogen content of maize seedlings,which increased by 29.05%,39.13%,33.96%,51.11% and33.27%,respectively,compared with spraying pure water.However,with the increase of urea concentration,root biomass,root surface area,root volume and nutrient concentrations such as N,P,K,Ca decreased significantly or slightly.In particular,when the foliar urea concentration reached 20%,the growth status and biomass of maize did not change significantly,but the root growth was significantly inhibited,and the root surface area,root volume,root tip number and average root diameter of maize decreased by 51.22%,69.88%,36.82% and 38.93%,respectively.Spraying urea could increase the nitrate concentration in leaves,but only 5% significantly increased the nitrate concentration in leaves,while the nitrate content in stems and roots had no significant change.With the increase of the urea concentration,the blade of the urea concentration also increased significantly,10%,20%,processing a small amount of transferred to stem,20% of a small amount of transferred to the roots,20% of leaf and root of ammonium nitrogen concentration increased significantly,the root of the ammonium nitrogen after spraying urea concentration increased to some extent,but there is no significant difference.Compared with the control spraying pure water,the moisture content of the upper part of corn field increased by 17.00%,6.16% and 5.38% after spraying 1%,2% and 5% urea on the foliar surface,respectively.In conclusion,proper urea spraying can effectively promote maize growth and increase vegetation coverage.By increasing the nitrogen concentration of maize,more nitrogen reserves could be provided for the later growth of maize. |
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