Water use in lowland rice cultivation in Asia: A review of evapotranspiration

Abstract

The literature on and basic principles affecting transpiration, evapotranspiration and the ratio of actual evapotranspiration to open pan evaporation (ET/EP) in wetland rice culture of South and Southeast Asia are reviewed. Based on existing information a simple model is suggested to predict evapotranspiration from wetland rice. Large differences in daily as well as seasonal total transpiration and evapotranspiration values exist for various locations. Crop transpiration rate is low at the early stage of growth and increases almost linearly, reaching 3–4 mm/day at maximum tiller number stage and 5–7 mm/day at heading time. Evapotranspiration also follows a similar trend for the maximum rate and varies with crop growth stage. The seasonal average evapotranspiration in wetland rice fields is in the range of 4–7 mm/day. The value of crop growth coefficient factor (ET/EP) is 1 at transplanting, reaching about 1.15 at maximum tiller number stage and around 1.3 at flowering stage. For a crop season this ratio is about 1.2 This information will aid significantly in developing better water management practices for rice.