Determination of Evapotranspiration and Crop Coefficient of Two Rice Cultivars in Mordab Plain (Guilan Province)

Since more than 75% of the rice fields in Iran are located in the Northern provinces i.e. Mazandaran, Guilan, and Golestan; identifying the crop water requirement of rice fields is essential for water resources planning in the Northern provinces. The objective of this research was to ascertain the crop water requirement of two rice cultivars namely Hashemi and Khazar in Guilan province during 1389 growing season. Four iron barrels with diameter of 56 cm were used as lysimeters to grow the cultivars mentioned. According to a simple volume balance approach the crop water use of the four lysimeters were determined during the growing season. The elements of volume balance approach such as the depths of drainage, precipitation, and irrigation were recorded daily and the average of 5-day and 10-day periods were reported. The daily rice crop water use during the growing season was found to range from 2.4 to 6.3 mm/day with a seasonal crop water use ranging from 430 to 470 mm for Hashemi and Khazar cultivars, respectively. Daily reference evapotranspiration was computed by the FAO-Penman-Montith equation and accordingly rice crop coefficients were computed. The crop coefficient of Hashemi variety was found to be 1.1, 1.3, and 1.1 during the initial, mid, and end growth stages, respectively. In addition, the aforementioned parameters for Khazar variety were 1.2, 1.3, and 1.1.