Investigation of Rice Actual Evapotranspiration and Crop Coefficients for Shiroudi and Hashemi Cultivars in Sari

Measuring the actual evapotranspiration rate of rice is too much important, in terms of appropriate and optimal water management of the Northern provinces in Iran. The present study aims to measure the actual evapotranspiration rate for two Shiroudi & Hashemi cultivars of rice, in Sari Agricultural and Natural Resources University’s paddy fields. For this propose, six drainage lysimeters were designed and constructed. After cultivating rice inside the designed lysimeters, the amount of precipitation, water content and deep percolation, were measured during 5-days periods. Investigation of the lysimeter results, shows difference between water requirement and also deep percolation of the two studied cultivars, in growth period (seeding to harvest steps); so that in these phases, water requirement rates was 350.81 & 396.67 millimeters and the deep percolation was 47.81 & 97.11, for the cultivars Shiroudi and Hashemi, respectively. Also the crop coefficient was obtained from the adaption of the lysimeter’s actual evapotranspiration and 14 indirect methods of reference evapotranspiration estimation, for the both cultivars. Considering the cultivar and estimating method, the crop coefficients are reported as the ranges 0.73-1.12 for the initial stage, 0.83-1.41 for the middle stage and 0.64-1.15 for the final stage. Also, the average estimation Error Percentage (PE) of the resulted crop coefficients compared to the recommended coefficients of FAO-Penmann56 method, is 11, 11 & 8 for Hashemi cultivar and 15, 23 & 16 for Shiroudi cultivar, in initial, middle and final stages respectively; which shows the necessity of extracting crop coefficients, for different cultivars under different local conditions. The obtained coefficients of the current study can be useful to calculate the water requirements of Hashemi and Shiroudi cultivars based on indirect estimation methods, for designing water projects, water delivery planning and also the irrigation and drainage networks in the research area.