Abstract: Evapotranspiration is the main pathway for water consumption in croplands and thus must be considered in cropland management and planning. We estimated the reference crop evapotranspiration of winter wheat in 2017 and 2018 in Zhengzhou agricultural meteorological experimental station from overwintering to maturity period by the PenmanMonteith formula. The actual evapotranspiration in the winter wheat cropland under the conditions of full irrigation (T2) and natural precipitation (T1) were measured using a largescale weighing lysimeter. The crop coefficients of winter wheat under both conditions were calculated. We analyzed the changes and their correlations with meteorological factors. The results showed that under different water conditions, the evapotranspiration of winter wheat showed a hump pattern. The evapotranspiration and fluctuation amplitude of T2 treatment were significantly higher than those of T1 treatment. The average total evapotranspiration of T2 and T1 treatments in the two years were 535.8 and 256.4 mm, respectively, while the average daily evapotranspiration in the corresponding period were 3.7 and 1.7 mm, respectively. Under the two water conditions, the average daily evapotranspiration was the highest at booting and heading stages and the lowest at overwintering stage. The crop coefficient of winter wheat under full irrigation conditions was significantly higher than the actual crop coefficient under drought stress. They generally showed a trend of decreasing, increasing and decreasing. In T1 treatment, the actual crop coefficient had the best correlation with air humidity, and the poorest correlation with average air temperature, while in T2 treatment, the crop coefficient had a good correlation with average temperature, total radiation, and wind speed, but a poor correlation with air humidity.

Key words: winter wheat, Penman-Monteith formula, evapotranspiration, crop coefficient.