Reduction of Ammonia Volatilization from Urea by a Floating Duckweed in Flooded Rice Fields

Effective nutrient management to reduce high N losses and to improve N use efficiency has been an important focus of agricultural and environmental science research. Understanding the influence of duckweed ( Lemna minor L.), a common floating macrophyte in flooded rice ( Oryza sativa L.) fields, on NH 3 volatilization and grain yield is required for better management of applied N fertilizer. We conducted an on‐farm experiment with three levels of urea (0, 90, 180 kg urea N ha −1 ) applied alone or in combination with duckweed. Our results indicate that total ammoniacal‐N concentration, pH, and temperature of the floodwater were significantly lower in the plots with a duckweed cover. As a consequence, NH 3 volatilization rates were reduced by duckweed from 20.0 to 53.7% and from 19.0 to 33.2% in plots supplied with 90 and 180 kg urea‐N ha −1 , respectively. Duckweed increased rice grain yields by approximately 0.7 and 0.7 Mg ha −1 (9.8 and 9.4%) in plots supplied with 90 and 180 kg urea N ha −1 , respectively. Ammonia losses from urea‐N applications can be reduced and N use efficiencies can be improved by the presence of duckweed in flooded rice fields.