Sawdust biochar application to rice paddy field: reduced nitrogen loss in floodwater accompanied with increased NH 3 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.