Biochar application mode influences nitrogen leaching and NH₃ volatilization losses in a rice paddy soil irrigated...

Impacts of biochar application mode on nitrogen (N) leaching, ammonia (NH₃) volatilization, rice grain yield and N use efficiency (NUE) are not well understood. Therefore, a field experiment was conducted to evaluate those impacts in a rice paddy soil received 225 kg N ha^-1 from either urea or N-rich wastewater. One treatment received 10 t ha^-1 biochar with the basal fertilization, and the other received same total amount of biochar but split applied with the three split N applications with same ratio as N fertilizer split ratio (40%, 30% and 30%). Results showed that N leaching loads were 4.20-6.22 kg ha^-1. Biochar one-time application reduced N leaching by 23.1%, and biochar split application further reduced N leaching by 32.4%. Total NH₃ volatilization loss was 15.5-24.5 kg ha^-1. Biochar one-time application did not influence the NH₃ volatilization, but biochar split application stimulated the cumulative NH₃ volatilization by 57.7%. Both biochar treatments had no influence on NUE and rice grain yield. In conclusion, biochar application mode indeed influences the N leaching and NH₃ volatilization in rice paddy soils, and biochar one-time application should be recommended for reducing N leaching without increasing NH₃ volatilization.