| In this paper, three treatments were set including bare land (CK), straw mulching (JF) and film mulching (DF). According to the measured data of winter wheat between 2013 and 2014 and the meteorological data, the reference crop evapotranspiration of winter wheat in Yangling during various growing periods was calculated through the adoption of Penman-Monteith formula, and the actual crop evapotranspiration was achieved by adopting the formula of field water balance equation. Hence, the variations of crop coefficients during different growing periods were analyzed. The results implied that straw mulching and film mulching could reduce the water requirement amounts by 13.07 mm and 17.86 mm, respectively, in winter wheat during various growth periods. Straw mulching had more sensitive response to water than the other two methods. Crop coefficients were shown to have a bimodal variation pattern throughout the entire growth period, while the summits appeared at the tillering-wintering and heading-filling periods. The two peaks in CK, JF, and DF treatments were 0.82 and 1.16, 0.89 and 1.05, and 0.87 and 1.13, respectively. At the same time, there were good forth-order-polynomial and second-order-polynomial correlations respectively between Kc and both the days after sowing and the cumulative temperature above 10℃, with correlation coefficients in JF and DF treatments above 0.88. |