Derivation of crop coefficients of three rice varieties based on ETo estimation method in Rasht region

Pirmoradian, Nader; Zekri, Fatemeh; Rezaei, Mojtaba; Abdollahi, Vaheedeh

Derivation of crop coefficients of three rice varieties based on ETo estimation method in Rasht region

Document Type : Research Paper

Authors

¹ Assist. Prof. Dept. of Water Engineering, Faculty of Agricultural Sciences, University of Guilan

² Graduate Student, Dept. of Water Engineering, Faculty of Agricultural Sciences, University of Guilan

³ Research Instructor of Rice Research Institute of Iran

Abstract

Determination of evapotranspiration is necessary in water studies specially to estimate crop water requirement and to design irrigation systems. One of the most important stages in estimating crop water requirement is determination of crop coefficient (K_c) and reference evapotranspiration (ET_o) as for factors such as growing period, crop species and cultivar. This experiment was conducted to derivate K_c for three rice varieties, Hashemi as a local cultivar, Khazar as an improved cultivar and Bahar as a Hybrid cultivar, in paddy fields of Rice Research Institute of Iran in 2009 and 2010. The values of crop evapotranspiration (ET_c) were measured with installing three cylindrical mini-lysimeter for each cultivar. Derivation of K_c were done based on five ET_o estimation methods including FAO Penman-Monteith, Radiation, Blaney-Criddle, Pan Evaporation and Hargreaves. As a result, water requirements for Khazar (526 mm) and Bahar (490 mm) varieties were 14.6 and 6.8 percent higher than Hashemi (459 mm) cultivar, respectively. The crop coefficients were varied between 0.76 to 1.09 for initial stage, 1.15 to 1.48 for mid-season and 0.91 to 1.21 for late-season based on ET_o estimation method and rice cultivar. Difference between the gained K_c in this study with the recommended values by FAO shows that derivation of crop coefficient based on local conditions is necessary. The obtained K_c based on different ET_o methods can increase estimation accuracy of water requirement in availability limitation to meteorological data. The results of this study can be used by local project managers, consultants and irrigation engineers in designing water projects and scheduling of water delivery in irrigation and drainage networks.

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