The lack of knowledge and data on the driving forces of nighttime (nocturnal) evapotranspiration (ET) for various vegetation surfaces under different climatic and management conditions led this study to investigate the magnitude of nighttime ET (ET night) and its interactions with other nighttime surface energy fluxes, i.e., soil heat flux (G night), sensible heat flux (H night), and net radiation (R n_night), and microclimatic variables, i.e., wind speed at 3 m (u 3_night), vapor pressure deficit (VPD night), and air temperature (T night). Soybean [( Glycine max (L.) Merr.)] canopies under two different irrigation methods in subsurface drip- and center-pivot irrigated (SDI and CP) fields in south central Nebraska were studied. Hourly energy flux and meteorological data from the SDI field for the 2007 and 2008 seasons and from the CP field for 2008 were analyzed. The study period was divided into five sub-periods based on plant and canopy development to evaluate nighttime energy balances and driving forces at various plant growth and development stages. The five sub-periods are: pre-planting (from mid-March to plant emergence, EM), early season (from emergence to full canopy cover, leaf area index, LAI
