| Summary: | The current water scarcity and world population increase cause the need for more food, pushing the demand on water resources due to crop production such as rice. Increasing agricultural water productivity by reducing the amount of irrigation water without affecting the yields, especially in paddy rice, is necessary. This is possible with alternate wetting and drying (AWD) irrigation. This study was conducted under greenhouse conditions at Tokyo University of Agriculture and Technology, Japan to evaluate the response of yield, water productivity and harvest index with different water regimes. The experiment was performed in pots with four water regimes as treatments and three replications, making 12 pots. The water regimes were continuous flooding irrigation as control and three AWD conditions—AWD5, AWD10 and AWD15—in which pots were irrigated when water reached 5, 10 and 15 cm soil depth, respectively, after the disappearance of surface ponding water. Yield components, harvest indexes and water productivity showed no significant difference (<i>p</i> < 0.05) between irrigation treatments. In this research, as there is more than a 25% reduction in water use and only 6.4% in grain yield, AWD15 was considered the best irrigation practice among the other treatments. This study provides data reference for theoretical scientific knowledge and understanding of safe AWD practice for countries facing water shortages.
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