Evapotranspiration and crop coefficient of drip irrigated walnut trees in semi-arid climatic conditions, Türkiye

This study was conducted tofind out the seasonal evapotranspiration (ETc) and crop coefficient (Kc) for walnut trees (ages one tonine) that were grown with drip irrigation inTrkiye’s semi-arid climate. Three different irrigation levels were applied atfive-day intervals based oncumulative Class Apan evaporation using irrigation treatment coefficients (Kt= 0.75, 1.00, and 1.25) during the 2015, 2016, 2017, 2018, 2019, 2021, 2022, and 2023 growing seasons. The amount ofirrigation water applied tothe treatments varied from year toyear according tothe measured Class Apan evaporation amounts. The total amount ofirrigation water applied tothe treatment subjects varied between 371.7mm and 619.6mm asan average ofeight years. Total ETcofwalnut trees varied over the years depending onthe applied irrigation water and measured rainfall. The total evapotranspiration estimated from the I2treatment, representing the irrigation regime inwhich 100% ofClass Apan evaporation was applied, fluctuated between 676.5 and 585.9mm over the study years. The daily reference evapotranspiration (ET0) values are calculated asbetween 1.85 and 7.07mm/day. The Kcvalues for walnut trees were calculated as 0.55 for April, 0.71 for May, 1.02 for June, 1.07 for July, 1.01 for August, and 0.74 for September on average. The research revealed that seasonal evapotranspiration and plant coefficient values can assist in calculating the water requirements of walnut trees and improve water management in semi-arid regions.