Abstract
Biochar (BC) potentially accelerates ammonia (NH3) volatilization from rice paddy soils. In this regard, however, application the floating duckweed (FDW) to biochar-amended soil to control the NH3 volatilization is not studied up-to-date. Therefore, the impacts of BC application with and without FDW on the NH3 and nitrous oxide (N2O) emissions, NUE and rice grain yield were evaluated in a soil columns experiment. We repacked soil columns with Hydragric Anthrosol and Haplic Acrisol treated in triplicates with Urea, Urea + BC and Urea + BC + FDW. Total NH3 losses from Hydragric Anthrosol and Haplic Acrisol were 15.2-33.2 kg N ha(-1 )and 19.6-39.7 kg N ha(-1), respectively. Urea + BC treatment recorded 25.6-43.7% higher (p < 0.05) NH3 losses than Urea treatment, attributing to higher pH value of floodwater. Floating duckweed decreased soil pH and therefore significantly reduced (p < 0.05) the NH3 volatilizations from the two soils by 50.6-54.2% over Urea + BC and by 34.2-38.0% over Urea treatment. Total N2O emissions from Hydragric Anthrosol and Haplic Acrisol were 1.19-3.42 kg N ha(-1) and 0.67 -2.08 kg N ha(-1), respectively. Urea + BC treatment increased N2O emissions by 58.8-68.7% and Urea + BC + FDW treatment further increased N2O emission by 187.4-210.4% over Urea treatment. Higher ammonium content of the topsoil, explained the N2O increases in the Urea + BC and Urea + BC + FDW treatments. Urea + BC slightly reduced the rice grain yield and NUE, while the Urea + BC + FDW promoted both rice yield and NUE. Our data indicate that co-application of FDW along with BC in paddy soil could mitigate the NH3 volatilization and enhance the rice grain yield and NUE. (C) 2019 Elsevier Ltd. All rights reserved.