Agricultural Research,Education and Extension Organization Journal of Water Research in Agriculture 2228-7140 35 3 2021 11 22 Estimation of Water Requirement and Crop Coefficients of Rice Cultivars Kuhsar and Hashemi in Different Cultivation Systems Estimation of Water Requirement and Crop Coefficients of Rice Cultivars Kuhsar and Hashemi in Different Cultivation Systems 235 245 125448 10.22092/jwra.2021.352374.833 FA Norollah Jalali PhD Student, Water Engineering Department, Sari Agricultural Sciences and Natural Resources University. Ali Shahnazari Professor, Water Engineering Department, Sari Agricultural Sciences and Natural Resources University. MZ Ahamadi Professor, Water Engineering Department, Sari Agricultural Sciences and Natural Resources University. Mojtaba Khoshravesh Associate Professor, Water Engineering Department, Sari Agricultural Sciences and Natural Resources University Mojtaba Rezaie Research Instructor, Rice Research Institute of Iran, Rasht, Iran. Journal Article 2020 12 08 The purpose of this study was to investigate the effects of irrigation management on water requirement and crop coefficient of Hashemi and Kuhsar cultivars in the first crop. This experiment was carried out in Mahmoudabad District of Mazandaran Province in Iran in the form of factorial in a randomized complete block design, in two growing seasons of 2016-2018. The water requirements for the fields (from transplanting to harvest) and the crop coefficient of these two cultivars were studied in two systems of traditional flooding and system of rice intensification (SRI).  The results showed that, in the first crop, the two-year average water requirements of Kohsar and Hashemi in SRI were 534 and 556 mm and for the traditional flooding system 623 and 632 mm, respectively. The water required by the farm in traditional flooding decreased by 13.1% in the SRI. Based on reference evapotranspiration using pan evaporation method for the three stages of vegetative, reproductive, and maturing, crop coefficient values for the flooding system for Kuhsar were, respectively, 1.14, 1.29, and 0.92; and for Hashemi, they were 1.18, 1.32, and 0.92. According to the obtained results, SRI causes significant savings in paddy water consumption, therefore, it is suggested that, due to water shortage in the country, this method be used as one of the adaptation strategies in rice fields. The purpose of this study was to investigate the effects of irrigation management on water requirement and crop coefficient of Hashemi and Kuhsar cultivars in the first crop. This experiment was carried out in Mahmoudabad District of Mazandaran Province in Iran in the form of factorial in a randomized complete block design, in two growing seasons of 2016-2018. The water requirements for the fields (from transplanting to harvest) and the crop coefficient of these two cultivars were studied in two systems of traditional flooding and system of rice intensification (SRI).  The results showed that, in the first crop, the two-year average water requirements of Kohsar and Hashemi in SRI were 534 and 556 mm and for the traditional flooding system 623 and 632 mm, respectively. The water required by the farm in traditional flooding decreased by 13.1% in the SRI. Based on reference evapotranspiration using pan evaporation method for the three stages of vegetative, reproductive, and maturing, crop coefficient values for the flooding system for Kuhsar were, respectively, 1.14, 1.29, and 0.92; and for Hashemi, they were 1.18, 1.32, and 0.92. According to the obtained results, SRI causes significant savings in paddy water consumption, therefore, it is suggested that, due to water shortage in the country, this method be used as one of the adaptation strategies in rice fields. https://wra.areeo.ac.ir/article_125448_0f9322dbcfa97fd1f3faf984cde2dc12.pdf