Grain yield and water use of irrigated rice under alternate wetting and drying irrigation as affected by contrasting weather conditions

Alternate wetting and drying (AWD) irrigation was developed to reduced water use in rice production. The effects of AWD on yield, water use, water quality, and greenhouse gas emissions are currently being evaluated at IRRI Farm, Los Baños [Philippines]. To discuss the strong and weak points of this technology, this poster focused on the results of the 2007 and 2008 dry season (DS) experiments with contrasting weather conditions. 2007 DS was drier than 2008 DS (56 and 121 mm rainfed, respectively) from transplanting to harvest. The experiments were conducted on split-split plot design with four replications. The main plot factor was water management (continuous flooding, CF; AWD-20 and AWD-70, which were irrigated when soil water potential at 15-cm-deep soil reached -20 and -70 kPa, respectively). Subplot factor was nitrogen (120 kg N/ha based on leaf color chart) by straw incorporation of 4 t/ha). In 2007 DS, grain yield of AWD-20 and AWD-70 were 18% and 22% lower than that of CF. In 2008 DS, no significant differences were observed in yield among water treatments due to the high amount of rainfall. In both seasons, water input became significantly lower under AWD compared with CF. In 2007 DS, AWD decreased water input by 21-31%, resulting in an irrigation water productivity of 0.32-0.60 kg cu m. In 2008 DS, irrigation water input to AWD plots was reduced further to 40-47%, thus, giving a higher irrigation water productivity of 0.42-1.35 kg/cu m. Results confirmed that AWD reduces water use in rice production and increases water productivity significantly. It also underscored the fact that the technology is vulnerable to yield penalty under drier weather conditions. With relatively stronger water stress in AWD-20 compared with the IRRI recommended safe AWD (10 kPa), further studies should explore more flexible irrigation management options in alleviating the affect of drier weather conditions. This will make high water productivity and stable yield more consistent.