determining crop coefficient of binam and khazar cultivars of rice by lysimeter and controlled basins in rasht region

estimating and determining of rice water requirement, being the main cultivate of rasht region, is crucial for devoting water to this region. equations which are used to calculate the reference evapotranspiration (et0) are not match to all climatic conditions, due to their empirical bases. so, it is necessary to clarify proper methods for each region. crop coefficient (kc) is also the main parameter for determining each plant’s potential evapotranspiration and subsequently plant water requirement. hence in this study, evapotranspiration data for grass and rice i.e. binam and khazar cultivars were collected in rice research institute of rash, by using drainable lysimeter at ten-day periods during three consecutive crop seasons. the reference evapotranspiration were calculated and compared with 16 empirical equations results included in ref-et software. significant differences of them have been evaluated using spss software. also, the crop coefficient values were calculated for each variety of rice. in all three equations i.e. hargreaves, priestley-taylor and penman (fao 24) have not shown any significant differences. among three methods, hargreaves equation is recommended for rasht region because, this equation as compared with others is a temperature-based method and would consider global warming phenomenon. also, the average of crop coefficient (kc) for khazar and binam in three consecutive crop seasons were 1.10 and 1.09, respectively.