Abstract: Water resources are a major constraint on agricultural development in arid areas. In recent years, with the development of watersaving irrigation technology, the contradiction between supply and demand of water resources was alleviated and the irrigation area was expanded. Understanding the evapotranspiration process of cropland under nonfull irrigating has great scientific significance to reveal the water cycle process and guide watersaving practices. In this paper, based on eddy covariance data in 2012 from Wulanwusu Agrometeorological Experiment Station, the evapotranspiration process of cotton filed in the different growth stages under mulched drip irrigation in Manas River basin of Xinjiang were analyzed. Furthermore, the crop coefficients of cotton under mulched drip irrigation were calculated based on the estimated evapotranspiration of reference crop by FAO-56 Penman-Monteith equation. The results showed that evapotranspiration and its rate of cotton field under mulched drip irrigation in oasis peaked in the flowering stage, with the phasic evapotranspiration of 248.51 mm and average daily evapotranspiration rate of 3.94 mm·d^-1. Followed by the values in the budding stage, the phasic evapotranspiration was 98.34 mm, and the average daily evapotranspiration rate was 3.18 mm·d^-1. The minimum values occurred in the sowing and seeding stages, the phasic evapotranspiration was 10.70 mm, and the average daily evapotranspiration rate was 1.07 mm·d^-1. In summary, the amount of evapotranspiration was 487.14 mm during the whole growing period, and the average crop coefficient was 0.42. The results of evapotranspiration and crop coefficients of cotton at different stages provide a scientific basis not only for rating and timing of irrigation of cotton at different growth stages but also for field water management.

Key words: mechanically harvested cotton, fiber quality, water use efficiency, seed cotton yield, nitrogen partial factor productivity, water and nitrogen regulation