Alternate wetting and drying (AWD) irrigation can save water in rice production while maintaining yields, but little is known about its influence on phosphorus (P) availability or fertiliser requirements. Plant-available P decreases as soil dries, causing P sorption and precipitation, and increases on rewetting, as P is released into plant-available soil fractions. This study examined how extent and frequency of wetting and drying cycles affect P availability in paddy soils. A pot trial showed dissolved inorganic P (DIP) concentrations in the soil increased with intensity of drying (continuously flooded: 1.1 mg P kg-1, re-flooded after drying to 66% moisture content: 2.2 mg P kg-1 and after drying to 5%: 5.1 mg P kg-1). In a field trial, DIP was higher following a double AWD cycle over a 30 day period (0.30 mg P kg-1) than following a single AWD cycle over the same period (0.1 mg P kg-1; Ptreatments; and no differences were found in grain yields when these AWD frequencies were continued through to harvest, probably because soil P concentrations were already at an agronomic optimum for rice. Five farmers interviewed reported using P fertiliser application rates in their AWD irrigation management that varied greatly from recommended levels. The study highlighted that AWD frequency could be managed to capture increases in DIP where P is limiting. Improvement in matching P fertiliser application to crop needs is more likely to produce significant savings regardless of irrigation method. Key words: Rice, water efficiency, irrigation, phosphorus, fertiliser application, Mekong