Measuring field ammonia emissions and canopy ammonia fluxes in agriculture using portable ammonia detector method

A comprehensive understanding of field ammonia (NH3) emissions and canopy ammonia fluxes in agriculture is beneficial for controlling ammonia pollution and achieving cleaner production. However, there is little consensus about ammonia emissions and fluxes in field conditions due to a lack of simple methods suitable for measuring field ammonia emissions and canopy ammonia fluxes. The study aimed to determine the feasibility of using portable ammonia detector (PAD) method for detecting ammonia emissions in rice and wheat fields, and elucidate related factors affecting ammonia emissions and fluxes. Four chamber methods were compared, i.e., closed static chamber (CSC), semi-open static chamber (SSC), dynamic flow-through chamber (DFC), and PAD method. Field ammonia emissions and canopy ammonia fluxes were determined using PAD method during two rice (2016 and 2017) and two wheat growing seasons (2016–2017 and 2017–2018). The contributions of soil ammonium (NH4+) concentration, soil temperature, and leaf area index to ammonia emissions and fluxes were assessed. The results showed that the PAD method was suitable for monitoring ammonia in field conditions, due to its great precision, accuracy, and sensitivity. During 2016, 2017 rice growing seasons, cumulative ammonia emissions from field surface was 12.31 and 13.48 kg N ha−1, cumulative ammonia fluxes in canopy was −0.340 and −0.379 kg N ha−1, and cumulative ammonia emissions above canopy was 11.97 and 13.10 kg N ha−1, respectively. During 2016–2017 and 2017–2018 wheat growing seasons, cumulative ammonia emissions from field surface was 9.71 and 9.29 kg N ha−1, cumulative ammonia fluxes in canopy was −0.506 and −0.423 kg N ha−1, and cumulative ammonia emissions above canopy was 9.20 and 8.87 kg N ha−1, respectively. Ammonia emissions were highly dependent on soil ammonium concentration. Greater ammonia emissions from field surface tended to increase net ammonia absorption by canopy. Overall, the PAD method is a promising method for measuring field ammonia emission and canopy ammonia flux in agriculture; ammonia emission from rice fields was greater than that from wheat fields, but net ammonia absorption by wheat canopy was greater than that by rice canopy.