Determining evapotranspiration and crop coefficients of young and mature pomegranate trees under drip irrigation*

In spite of the importance of increasing water shortages in most pomegranate production regions, there is not sufficient information about the water requirement and crop coefficients (Kc) of pomegranate trees under various conditions (e.g., plant cultivar and age and irrigation system). The aim of this study was to measure evapotranspiration during three growing seasons (2013, 2015, and 2016) and to determine Kc of young and mature pomegranate (Punica granatum L.) trees under drip irrigation in Iran. The soil water balance approach was applied to determine crop evapotranspiration (ETc) using soil water content measured during the growing seasons. The ratio of measured ETc to reference evapotranspiration calculated according to the Penman–Monteith equation provided the Kc values. According to the findings, from bud burst to peak season, daily Kc values for young pomegranate trees ranged from 0.18 to 0.70, 0.22 to 0.89, and 0.23 to 0.95 in 2013, 2015, and 2016, respectively. For mature pomegranate trees, these values varied between 0.26 to 1.15, 0.21 to 1.25, and 0.30 to 1.08 in 2013, 2015, and 2016, respectively. From bud burst to peak season, the total ETc for young pomegranate trees was 711, 905, and 934 mm and for mature pomegranate trees 1,172, 1,086, and 1,138 in 2013, 2015, and 2016, respectively. The results of this study are applicable to accurate water allocation, precision irrigation scheduling, and design of irrigation systems in pomegranate orchards.