Sawdust biochar application to rice paddy field: reduced nitrogen loss in floodwater accompanied with increased NH3 volatilization.

Sawdust biochar (SDB) was for the first time applied to rice paddy field to evaluate its effects on potential nitrogen (N) runoff and ammonia (NH3) volatilization losses in a soil column experimental system. Results showed that total N concentration of surface floodwater under SDB treatments was reduced by 7.29-35.16, 16.34-32.35, and 12.21-28.12% after three split N fertilizations, respectively. Particularly, NH4+-N was decreased by 11.84-27.08, 14.29-36.50, and 2.97-19.64%, respectively. However, SDB addition has no significant influence on NO3--N concentration. Meanwhile, SDB application increased NH4+-N and total N content of top (0-15 cm) soil. Furthermore, these SDB-induced influences were more pronounced for 3 wt% SDB treatments. SDB treatments recorded 3.56-5.78 kg ha-1 higher NH3 volatilization than urea control treatment, which was attributed to the elevated pH values of floodwater and top soil induced by SDB. Fortunately, the yield-scale NH3 volatilization was not increased dramatically.