The Suitability Of PAD Method For Measuring Ammonia Flux In Field

Ammonia emissions from agricultural production activities are an important source of ammonia pollution in the atmosphere.Monitoring and quantifying ammonia emissions from field is of great theoretical and practical significance for scientific and accurate development of ammonia emission inventories and formulation of countermeasures for air pollution prevention and control.Due to the active nature of ammonia,the concentration of ammonia in the field atmosphere is very low and is a trace gas,and there is a lack of effective,rapid,accurate and reliable monitoring methods.The conventional aeration-type acid absorption method is time-consuming and laborious,so a new method for simple,rapid and accurate monitoring of ammonia volatilization in field is urgently needed.In this study,we investigated the suitability of the portable ammonia detector（PAD）method for determining ammonia volatilization in agricultural fields by using the conventional aeration acid absorption（AAA）method as a control,indoor simulated incubation tests and field trials.The main findings of the study are as follows:Indoor simulations showed that:（1）the determination results of PAD and AAA method had the same trend,the volatile flux of ammonia increased with the increase of nitrogen application;the volatile flux of ammonia increased with the increase of air temperature;the minimum determination limit of PAD was 0.1 mg N m^-2d^-1;the suitable temperature range for PAD determination was above 5℃.（2）The effect of air humidity on the determination of PAD varied with the amount of nitrogen applied,and increased with the increase of humidity at medium and low nitrogen application rates.（3）The results of the PAD method were comparable to or higher than those of the AAA method at low N application rates,while the AAA method was significantly higher than the PAD method at medium and high N application rates.Field trials showed that:（1）under low pre-winter temperatures,the peak ammonia volatilization in the nitrogen application treatment measured by the AAA method was much higher than that measured by the PAD method,which measured 9.72 kg N ha^-1and 9.53 kg N ha^-1for wheat and barley,respectively,and 8.37 kg N ha^-1and 8.21 kg N ha^-1for wheat and barley,respectively,without nitrogen application;the AAA method measured soil ammonia volatilization accumulation of 13.22 kg N ha^-1and 14.00 kg N ha^-1for wheat and barley,respectively,and 7.08 kg N ha^-1and 7.45 kg N ha^-1for wheat and barley,respectively,without nitrogen application.（2）The correlation between soil ammonia fluxes measured by the two methods is highly significant and positive;the measurement conditions of PAD are closer to the real environment of field than the AAA method,and the correlation between soil ammonia fluxes and soil NH₄⁺-N concentrations measured by PAD is better than that of the AAA method;therefore,PAD has the potential to be applied to the monitoring of ammonia volatilization in large fields and is suitable for the rapid monitoring of ammonia volatilization in field.