Ammonia Volatilization Of Winter Wheat Canopy Under Different Nitrogen Rates

Ammonia volatilization is an important pathway of nitrogen loss from agricultural systems.However,the research on farmland system of ammonia volatilization more concentrated on soil for a long time,little is known about the effect of crop canopy.Lack of continuous tracking for canopy ammonia volatilization limits the understanding of canopy ammonia volatilization mechanism.It is of great importance for improving fertilizer-N use efficiency and atmospheric environment quality to study the ammonia exchange process between crop canopy and atmosphere and its mechanism.A single factor field experiment with three nitrogen rates?0,90,and 180 kg N·ha-1?was conducted in winter wheat during the 2015²016 growth season.The aim is to study dynamics and main influence factors of ammonia volatilization of canopy and its contribution rate for winter wheat field.Ammonia volatilization from both soil and canopy in winter wheat field were measured with the modified vented ammonia trap chambers.Winter wheat canopy ammonia volatilization rate and its relationship with leaf nitrogen physiological indexes were analyzed in situ.The effects of nitrogen treatments on grain yield and yield components,ammonia volatilization intensity,biomass,nitrogen use,and nitrogen translocation and relationships of those indexs with canopy ammonia volatilization were analyzed.The main results are listed as followes:a)Field ammonia volatilization mainly occurred within the 2³ weeks after N fertilization.In the whole growing season,ammonia volatilization totaled in 3.773⁸.704 kg N·ha-1,and it increased significantly with the increase of N fertilization rates,of which 3.289⁷.773 kg N·ha-1 were from soil,accounting for 87.2⁸9.3% of the total;and 0.750¹.461 kg N·ha-1 from the canopy,accounting for 15.4¹9.9% of the total.b)Canopy ammonia exchange affected by the applied amount of N fertilizer and reproductive period during the vegetative period.Canopy absorbed volatilized ammoniaduring seedling stage under lower nitrogen application rate?N90?,and during seedling,returning green and early grain filling stage under higher N application rate?N180?,but did not under no N fertilization.The net canopy ammonia volatilization mainly occurred at flowering and late grain filling stage,and its not affected by the applied amount of N fertilizer,accounting for 4.5⁹.3% and 79.1⁹9.0% of total canopy ammonia volatilization during the whole growing season,respectively.c)Canopy ammonia volatilization affected by plant physiological factors and external environment factors.It was found that the canopy ammonia fluxes were positively correlated with the ammonia compensation point,apoplastic NH₄⁺ concentration,air temperature and soil temperature,but showed no relation to the glutamine synthetase?GS?activity in leaves,apoplastic pH and relative air humidity.The ammnonia volatilization increased with the air temperature,since the air temperature affected ammonia compensation.Soil temperature plays an important role in changing air ammnoia concentration and leaf ammonia compensation point for ammnonia volatilization of canopy.d)Nitrogen application can significantly improve the winter wheat grain yield,yield components.Spike density is decisive key elements for grain yield.Increase the biomass and harvest index is the prerequisite of high grain yield.Nitrogen application can significantly improve the plant biomass,nitrogen amount of canopy organs,nitrogen translocation amount and nitrogen translocation efficiency of canopy organs.However,nitrogen fertilization decreased apparent nitrogen recovery,agronomic nitrogen effiviency,physiological nitrogen efficiency.Moreover,nitrogen fertilization can improve unit grain yield corresponding ammonia volatilization loss from the soil and wheat fields?ammonia volatilization intensity?.e)Accumulative canopy ammonia volatilization was positively correlated with biomass,plant nitrogen uptake,grain nitrogen uptake,nitrogen translocation amount of canopy organs.Leaf is the main organ of canopy ammonia volatilization,the more biomass and nitrogen content of leaf,the more accumulative canopy ammonia volatilization.Moreover,leaf nitrogen transport provides the material of canopy ammonia volatilization at the late growth stage,accumulative canopy ammonia volatilization were positively correlated with nitrogen translocation amount of leaf.