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Plastic film mulch has been widely adopted in recent decades in the arid region of northwest China, and the practice changes the energy budget of the soil surface, crop water use and plant growth and yield. However, there are few studies that quantify differences in the energy balance, water use, plant growth and water use efficiency (WUE) with and without plastic film mulch. Energy components, crop evapotranspiration, plant growth and yield were measured in a mulched (M) and unmulched (NM) maize field in 2014 and 2015. The results showed that diurnal net radiation (R-n) was lower while soil heat flux (G) was higher for the M treatment than in the NM on typical sunny days. Diurnal pattern of G was the same as R-n but the maximum lagged by 0.5-2 h. For the M treatment, the duration of R-n > 0 was less than that of the NM for 96 days, i.e., 61% of the whole growth period. Plastic film mulch decreased daily R-n, as the linear regression of R-n with the R-n of unmulched treatment had a slope of 0.90. Plastic film mulch reduced ET as the available energy decreased. The total ET was 524 and 557 mm with daily mean values of 3.3 and 3.5 mm d(-1) in 2014, and 550 and 575 mm with daily mean values of 3.5 and 3.7 mm d(-1) in 2015 for M and NM, respectively. A better curvilinear relationship was found between ET for M and NM for two years, with R-2 of 0.95 and 0.90, respectively. The plastic film mulch decreased crop coefficient but accelerated plant growth and advanced maize maturity, and thus increased yield and WUE. (C) 2016 Elsevier B.V. All rights reserved.