Two-Minute Onsite Detection of Agricultural Water Nitrogen Pollution with an Ammonia Gas Sensing System

Nitrogen pollution from agriculture is one of the major environmental problems. A high proportion of the fertilizers leached into the environment by runoff water, causing eutrophication and biodiversity damage. This study employed a semiconductor ammonia gas sensor to detect total ammonia nitrogen (TAN) pollution through fertilization as ammonia emissions correlate with the aqueous ammonium ion concentration. The sensor has a vertical conduction channel and a high sensitivity. The gas method is compared with the conventional indophenol method. It shows consistent results from the drinking water criterion of 0.5 mg/L to the acute criterion of 17 mg/L nitrogen pollution. The gas method is more convenient. For a given nitrogen dose, by comparison of two kinds of popular fertilizers, ammonium sulfate and urea, the lower ammonium concentration for urea is discovered. This gas sensor was applied to track the TAN runoff of the rice field to reveal that after base fertilization, there is an ammonium shock exceeding regulations. Therefore, real-time monitoring is necessary to assess the time-dependent environmental impacts and develop optimized fertilization schedules considering the cost of fertilization and the environment. The gas sensor is an ideal tool for these approaches to controlling nitrogen pollution.