Soil & Water Res., X:X | DOI: 10.17221/72/2025-SWR

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

Tolga Erdem ORCID...1, Erhan Göçmen ORCID...1, Mehmet Şener ORCID...1, Zafer Çoşkun ORCID...2, Ahmet Semih Yaşasın ORCID...2, Buse Önler1
1 Department of Biosystems Engineering, Faculty of Agriculture, Tekirdağ Namık Kemal University, Tekirdağ, Türkiye
2 Tekirdağ Viticulture Research Institute, Tekirdağ, Türkiye

This study was conducted to find out the seasonal evapotranspiration (ETc) and crop coefficient (Kc) for walnut trees (ages one to nine) that were grown with drip irrigation in Türkiye’s semi-arid climate. Three different irrigation levels were applied at five-day intervals based on cumulative Class A pan 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 of irrigation water applied to the treatments varied from year to year according to the measured Class A pan evaporation amounts. The total amount of irrigation water applied to the treatment subjects varied between 371.7 mm and 619.6 mm as an average of eight years. Total ETc of walnut trees varied over the years depending on the applied irrigation water and measured rainfall. The total evapotranspiration estimated from the I2 treatment, representing the irrigation regime in which 100% of Class A pan evaporation was applied, fluctuated between 676.5 and 585.9 mm over the study years. The daily reference evapotranspiration (ET0) values are calculated as between 1.85 and 7.07 mm/day. The Kc values 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.

Keywords: irrigation regimes; irrigation water use; precipitation; reference evapotranspiration

Received: June 16, 2025; Accepted: March 16, 2026; Prepublished online: March 27, 2026 

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