Climate-Smart Water and Nitrogen Management Strategies for Lowland Rice
World Nitrogen (N) fertilizer consumption is around 100 million metric tons and is expected to increase with growing food production. However, the N use efficiency with current surface application of urea is extremely low (35-40%) due to its losses from ammonia volatilization, nitrification, denitrification and runoff, particularly under flooded rice cultivation. N losses disrupt natural ecosystems, impair water quality and contribute to global warming (nitrous oxide [N2O] emissions). Climate-smart technologies maximize synergies while minimizing tradeoffs associated with increased productivity and sustainable farmer income, reduced environmental pollution and reduced vulnerability to climate variability and risks. Technologies that reduce environmental footprint without sacrificing productivity, farmer income and sustainability are more likely be adopted by farmers. Modified urea-N fertilizers and/or subsurface application have resulted in significant reduction in N losses and increased productivity. In Bangladesh subsurface application of urea – urea deep placement (UDP) – has increased rice yield by 15-18% while reducing N use by one-third compared with broadcast urea. UDP also resulted in significant reduction in N volatilization loss (<5% vs. 25-35% with conventional application) and N2O emissions. N2O emissions from UDP fields were as low as emissions from unfertilized N plots, ranging from 20-50 g N2O-N ha-1 (wet season) to 100-160 g N2O-N ha-1 (dry season). Moreover, the drudgery of deep-placement was reduced with the use of affordable applicators, and, combined with a single N application and reduced weeding, it decreased labor requirement by 15-25% compared to broadcast urea. UDP technology has proven to be an effective climate-smart agricultural practice that increases the food production and wellbeing of poor rice farmers and reduces GHG emissions through the combination of reduced N fertilizer use and reduced N losses. Preliminary results also show reduced N2O emissions from UDP under alternate-wetting and drying conditions (AWD). The combination of UDP and AWD resulted in reduced N2O and methane emissions, water saving and higher grain yield compared to continuously flooded conditions with conventional application of urea.