Abstract
Dastane (1974) recommended four different methods, namely evapotranspiration-rainfall ratio method, Indian-1 and Indian-2 methods and Vietnam method for estimating effective rainfall for rice crop. These methods together with the USDA-SCS method were compared against the physicallybased water balance method. The analysis was carried out using daily data of evapotranspiration (ET) and rainfall pertaining to thirteen seasons with special reference to lowland paddy rice in South India. Among the different methods, the ET-rainfall ratio and Indian-2 methods estimate the effective rainfall values nearly closer to those by the water balance method. The USDA-SCS method underpredicts values of effective rainfall compared to other methods. The ET-rainfall ratio and Indian-2 methods can be used as alternatives to the water balance method for determining effective rainfall which in turn be used in estimating irrigation requirements for lowland rice.
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