The characteristics of evapotranspiration and crop coefficients of an irrigated vineyard in arid Northwest China

Oasis effect may have significant impacts on the crop water use in irrigated fields of extremely arid conditions. Studies on crop coefficients and its relevant influence factors are essential to accurately determine the irrigation scheduling under such conditions. A two-year experiment was conducted in an irrigated vineyard to estimate evapotranspiration (ET) and its two components: evaporation (E) and crop transpiration (T), and to develop appropriate region-specific crop coefficients (Kc, Kcb) in arid Northwest China. The contributions of “oasis effect” to Kc, the relationships of both Kc and Kcb to canopy conductance (Gc) and leaf area index (LAI) were investigated. Local values of Kc for evapotranspiration and crop transpiration (Kcb) were calculated using the field data and the dual-Kc approach. The daily ET ranged from 0.80 to 9.87 mm d−1 and from 0.99 to 8.73 mm d−1 in 2014 and 2015, respectively, with corresponding T/ET values amounting to approximately 58.4% and 55.1%. The locally averaged Kc values were 0.79, 1.31, and 1.08 during the initial, middle, and late growth stages, respectively, versus corresponding Kcb values of 0.17, 0.97, and 0.64. Arid advection accounted for 16.9 to 57.4% and from 1.4 to 49.0% of daily Kc during the two study periods. Both Kc and Kcb to LAI is a linear regression but to Gc is an exponential one. LAI is a better indicator than Gc when it is used to predict Kc and Kcb. These results will help growers to improve irrigation efficiency and quantify the contributions of individual factors to Kc and Kcb in such conditions.