Study On Determination Method Of Ammonia Emission Of Greenhouses Based On Micrometeorological Technology

The high multi-investment index of the vegetable field and the excessive use of chemical fertilizer are the main factors affecting the ammonia discharge of the farmland.Meanwhile a large amount of ammonia emission lead to environmental problems such as increased ammonia deposition,increased atmospheric PM_2.5 concentration and increased greenhouse effect.In recent years,research has been conducted on ammonia discharge from facility vegetable fields,but it is generally believed that the estimation of soil ammonia emissions by in situ ventilation is low.In addition,the gas diffusion system in the solar greenhouse is relatively complicated and the in situ ventilation method can not truly reflect the discharge of ammonia to the outdoor shed.In order to accurately assess the environmental impact of ammonia emission from facility vegetable fields caused by nitrogen fertilizer application,it is particularly important to find a method for accurately measuring ammonia emissions.In this study,the micro-meteorological method was used to measure the ammonia emission rate and emissions in solar greenhouses in North China,and the applicability of micro-meteorological methods in greenhouse ammonia emissions was discussed.The difference between ammonia emission characteristics and nitrogen loss ratio measured by in situ ventilation method was compared.The main conclusions areas follows:?1?The selection of the underlying surface had a significant influence on the ammonia emission estimation.The measured heights z-d and z are obtained with the zero plane of the 67%shed height and the underlying surface of the shed area.In spring and summer,the emission rate and amount under z-d condition are approximately 69%and 80%,respectively,for the discharge rate under z condition.?2?The emission source area had no significant effect on the ammonia emission rate.It was estimated by the total area of all sheds?SA?and all areas?LA?in the shed area.Under the same measurement height,the emission rate of LA in spring and summer were approximately 1.54 and 1.45 times than LA.The total emissions under SA condition in spring and summer were about 5.3-5.4%and 1.4-1.9%higher than those under LA condition,respectively,and the difference was not significant.?3?When measured by TDLAS-bLS method,the NH3-N loss in tomato greenhouse in summer was about 10.16 kg/hm²,accounting for 7.1%of total nitrogen application.The ammonia emissions during the topdressing period of cabbage and watermelon were 13.36kg/hm² and 16.24 kg/hm²,respectively,while the nitrogen loss rate was 11.9%and 31.9%,respectively.?4?When measured by in situ ventilation method,the ammonia emission of cabbage was higher than that of non-strip application area,and the ammonia emission was 1.04kg/hm²/d and 0.58 kg/hm²/d respectively.Ammonia emission nitrogen loss were 1.35kg/hm² and 1.64 kg/hm²,and nitrogen loss ratio was 0.3%and 0.4%,respectively.For the top dressing fertilizer ammonia nitrogen loss amount were 1.26 kg/hm² and 0.98 kg/hm²,respectively,and the nitrogen loss ratio was 1.5%and 1.0%,respectively.?5?The results of nitrogen loss ratio measured by TDLAS-bLS method and in situ ventilation method were quite different,and the method needs to be further improved and verified.In summary,when the TDLAS-bLS method used to measure the protection of ammonia emission,the determination of the underlying surface relative to the area of the emission source is the main factor affecting the ammonia emission rate of soil.The results of the two methods are quite different,and the ammonia emission from the vegetable fields need further study.