Alternate wetting and drying (AWD) irrigation is a water saving irrigation technique in rice production and can be
an important adaptation strategy under climate change where water scarcity may become more prevailing. The
suitability of AWD in acid sulphate soils (ASS) has not been tested. There is a possibility that the drying cycles of AWD may enhance oxidation and acidification. The drying cycles may also reduce the phosphorous availability to the plants. Rice irrigated with AWD may require more P fertilizer than under continuous flooded condition. In highly intensive cropping areas of the Mekong river delta of Viet Nam, such as An Giang province, farmers have applied high doses of P fertilizer to compensate for the P-binding of toxicities associated with ASS such as aluminum and iron. Excess of P, on the other hand can lead to phosphorous accumulation over time. This may reduce the requirement for P fertilizer input, even under AWD irrigation. This study investigated the interacti ve effects of AWD irrigation and phosphorous rates on on water use, soil properties, rice growth and yield in double rice system grown on ASS in Ta Danh, An Giang, for 3 consecutive crops from March 2012 to June 2013. AWD application reduced about 50% of irrigated water quantity and increased EC value of field water in contrast with continuous flooded of farmers’ practice. Difference in water management strategies and phosphorous levels showed no impact on pH values of field water, rice growth, biomass accumulation, and rice yield in 3 continuous cropping se asons. Without or reduced phosphorous fertilization varied the availability of phosphorous in the soil for at least 2 crops that could waste farmers’ resource and create environmental issues. Obtained data promote the application of AW D irrigation and less phosphorous use for rice production in acid sulphate soil to improve resource management and local farmers’ adaptation under impact of climate change.