Assessment and Estimation of Evapotranspiration of Rice Plant in Northern Provinces of Iran

Oryza sativa is one of the crops which can be cultivated in warm and humid climates with relatively high rainfall or large areas of terrestrial water and underground water. One of the most suitable region for rice growing is the northern provinces of Iran. In this study, the rate of evapotranspiration of Oryza sativa in different stages of growth (May to August) has been obtained in three provinces of Iran (Gilan, Mazandaran and Golestan). First, the evapotranspiration of the reference plant in selected stations was calculated using the FAO Penman-Monteith method, and then by the product of the rice plant's coefficient in the reference values of evapotranspiration, the amount of evapotranspiration of Oryza sativa was obtained at different stages of growth. The results indicate that the maximum evapotranspiration of the Oryza sativa in the middle stage and the minimum of this index occurred in the final stage of grows (except Manjil station). Also, the evapotranspiration in the middle stage of grows (June and July) is around 65 – 70 % of the total evapotranspiration in the most stations. The rate of evapotranspiration of rice in all stages of growth decreases from the east (Marave tappeh station) to the west (Astara station) of the region (except Manjil station). In contrast, the rate of precipitation during the period of growth of this product from east to west is increasing. For instance, the precipitation at Marave Tappeh and Gorgan are supplied respectively 9 and 20% of the water demand of this product while in the stations of Mazandaran and Gilan provinces, about 30-50% of the water demand of this product is provided by rainfall.