Nitrogen Use Efficiency, Crop Productivity and Environmental Impacts of Urea Deep Placement in Lowland Rice Fields

Nitrogen (N) fertilization is critical for cereal production; however, its low use efficiency poses both economic and environmental concerns. Urea deep placement (UDP) in lowland rice fields is one of the best currently applicable management techniques to increase N use efficiency (NUE) and crop productivity. Multi-location experiments conducted in Bangladesh in 2014-2015 have demonstrated several benefits of UDP use including reduced N losses through ammonia volatilization and greenhouse gas nitrous oxide (N2O) and nitric oxide (NO) emissions. Nitrogen loss as N2O and NO emissions were measured continuously throughout rice-growing and fallow seasons using an automated gas sampling and analysis system. Across the years and sites, UDP increased yield on average by 21% as compared to broadcast urea while using at least 25% less fertilizer. UDP reduced floodwater ammonium and ammonia volatilization similar to the control (N0) treatment, while both were significantly higher in broadcast urea treatments. UDP reduced N2O emissions by up to 80% as compared to broadcast urea under continuous flooded (CF) conditions. The effects of UDP on N2O emissions under alternate wetting and drying (AWD) irrigation practices were site specific: depending on the duration and intensity of soil drying, emissions were reduced under mild soil drying but increased with more intense soil drying. These results confirm that UDP not only increases NUE and grain yields but also reduces negative environmental impacts including N2O emissions.
Deep placement, Greenhouse gas emissions, Rice, Environment