Biochar manure decreases ammonia volatilization loss and sustains crop productivity in rice paddy

Manure application is a recommended method to improve soil quality and mitigate global warming via soil carbon (C) sequestration. However, such application can significantly increase ammonia (NH 3 ) volatilization loss and cause secondary environmental problems, such as acidification, eutrophication, and particulate matter formation. To investigate the potential of reducing NH 3 emissions in flooded rice paddies, three types of stabilized swine manure amendments (fresh, composted, and biochar) were applied at a rate of 12 Mg ha −1 (dry weight) under standard fertilization (N–P 2 O 5 –K 2 O = 90–45–57 kg ha −1 ), and NH 3 emission was characterized using the static chamber method. Regardless of manure management practices, NH 3 fluxes increased significantly immediately after application of an inorganic nitrogen (N) fertilizer (urea). The manure was applied completely as the basal fertilizer before rice transplanting, but the NH 3 emission rates increased more dramatically following urea application in the manure treatments. Fresh and composted manure applications significantly increased seasonal NH 3 volatilization losses compared to the control but the biochar did not. Compost manure significantly increased rice grain productivity owing to the higher N content, while fresh and biochar manures did not increase rice productivity because of fewer panicles per hill and fewer grains per panicle. Consequently, biochar application resulted in lower NH 3 flux intensity and seasonal NH 3 flux per grain yield, whereas fresh and compost manures substantially increased this intensity. Therefore, biochar manure may be a more reasonable organic amendment than fresh and composted manures for reducing NH 3 emission impacts on rice paddies.