Controlled-release fertilizer, floating duckweed, and biochar affect ammonia volatilization and nitrous oxide emission from rice paddy fields irrigated with nitrogen-rich wastewater

It is of great concern that nitrogen-rich (N-rich) wastewater irrigation increases ammonia (NH3) volatilization from rice (Oryza sativa L.) paddy fields. A pilot-scale field trial was conducted to study the impact of different management practices on reducing NH3 volatilization and their subsequent impacts on nitrous oxide (N2O) emission from a paddy field irrigated with N-rich wastewater generated by livestock production and supplemented with urea N fertilizer. A total of 225 kg N ha−1 combined with urea and N-rich wastewater was split into basal, the first, and second supplementary applications for the following five treatments: urea N mixed with controlled-release N fertilizer (BBF), floating duckweed (FDW), biochar alone (BC), biochar mixed with calcium superphosphate (BCP), and control with no amendment (CK). Results showed that each treatment had similar pattern of NH3 volatilization and N2O emission after N application. Treatments of BBF, FDW, and BCP effectively reduced NH3 losses by 22.8, 55.2, and 39.2 %, respectively, compared with the CK. BBF treatment decreased NH3 volatilization after the first supplementary N fertilization; BCP treatment reduced NH3 volatilization after the basal fertilization; and FDW treatment reduced NH3 volatilization after both the basal and first supplementary fertilization. Besides controlling the NH3 volatilization, BCP treatment also reduced 19.5 % of N2O loss. However, BC alone suppressed N2O emission by 24.3 %, but did not reduce NH3 loss. The findings can practically guide farmers to choose the appropriate management practices in improving N use efficiency and minimizing the impact of fertilization on environmental quality.