- Purpose: Both fresh water and phosphorous resources have gradually become rare in rice production

- Approach and methods used: In this farmer field experiment, alternate wetting and drying irrigation and reduced phosphorous application were applied simultaneously to double rice area at Ta Danh Commune, Tri Ton district, An Giang province, Mekong Delta, in the South of Vietnam to calculate their contribution for rice culture profitability.

- Key results: Water-saved irrigation technique increased the pumping interval in contrast to that of continuous flooding application and saved from 30 to 50% of irrigated water quantity depending on crop season. During cropping season, the field surface of water-saved plots became dry in an occasional duration of many several days but the measured pH and EC values of field water were not significant difference from those of continuous flooded ones. Reduced or without phosphorous fertilization in 3 consecutive crops showed no change in available phosphorous level in the soil and its content in plant materials. Combination of alternate wetting and drying irrigation and phosphorous reduction caused no impact on OM4218 rice cultivar growth, above ground biomass accumulation, and yield in 3 successive crop seasons. No interaction was found between the two experimented factors but their jointed application increased the farmer income in each rice crop about 4 millions VND (~ 200 USD) per ha.

- Synthesis and Applications: Alternate wetting and drying irrigation technique appears as an adaptive strategy for rice production under climate change but the sustainability of phosphorous reduction on acid sulphate soil in Mekong Delta requires further investigation.