An Alternate Wetting and Moderate Soil Drying Regime Improves Root and Shoot Growth in Rice

A major challenge in rice (Oryza sativa L.) production is to achieve the dual goal of increasing food production and saving water. This study aimed to investigate if alternate wetting and drying regimes could improve root and shoot growth and consequently increase grain yield and water use efficiency (WUE). Two rice varieties were field-grown at Yangzhou, China in 2005 and 2006. Three irrigation regimes, alternate wetting and moderate soil drying (WMD, re-watered when soil water potential reached -15 kPa at 15-20 cm depth), alternate wetting and severe soil drying (WSD, re-watered when soil water potential reached -30 kPa), and a conventional irrigation (Cl, continuously flooded), were imposed during the whole growing season. Compared with the Cl, the WMD regime significantly increased, whereas the WSD regime reduced, root oxidation activity, cytokinin concentrations in roots and shoots, leaf photosynthetic rate, and activities of key enzymes involved in sucrose-to-starch conversion in grains. Grain yield of the two varieties, on the average, was increased by 11% under the WMD regime, and was reduced by 32% under the WSD regime when compared with that under the Cl regime. Averaged WUE of the two varieties was increased by 55% under the WMD regime and 36% under the WSD regime. We conclude that a moderate wetting and drying regime can enhance root growth which benefits other physiological processes and result in higher grain yield and WUE.