Floating duckweed mitigated ammonia volatilization and increased grain yield and nitrogen use efficiency of rice in biochar amended paddy soils.

Biochar (BC) potentially accelerates ammonia (NH) volatilization from rice paddy soils. In this regard, however, application the floating duckweed (FDW) to biochar-amended soil to control the NH volatilization is not studied up-to-date. Therefore, the impacts of BC application with and without FDW on the NH and nitrous oxide (NO) 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 NH losses from Hydragric Anthrosol and Haplic Acrisol were 15.2-33.2 kg N ha and 19.6-39.7 kg N ha, respectively. Urea + BC treatment recorded 25.6-43.7% higher (p < 0.05) NH losses than Urea treatment, attributing to higher pH value of floodwater. Floating duckweed decreased soil pH and therefore significantly reduced (p < 0.05) the NH volatilizations from the two soils by 50.6-54.2% over Urea + BC and by 34.2-38.0% over Urea treatment. Total NO emissions from Hydragric Anthrosol and Haplic Acrisol were 1.19-3.42 kg N ha and 0.67-2.08 kg N ha, respectively. Urea + BC treatment increased NO emissions by 58.8-68.7% and Urea + BC + FDW treatment further increased NO emission by 187.4-210.4% over Urea treatment. Higher ammonium content of the topsoil, explained the NO 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 NH volatilization and enhance the rice grain yield and NUE.