Single and dual crop coefficient methods are used in conjunction with grass reference evapotranspiration (ET o ) to estimate actual crop evapotranspiration (ET c ). However, the impact of soil surface residue cover on the accuracy of ET c estimated with these methods is not well understood. The objective of this study is to evaluate and compare the accuracy of the FAO-56 single crop coefficient (single-K c ) and dual crop coefficient (dual-K c ) methods for estimating soybean [Glycine max (L.) Merr.] ET c in a partially residue covered field. The study was conducted at the University of Nebraska-Lincoln, South Central Agricultural Laboratory (SCAL), Nebraska, during the 2007 and 2008 growing seasons. The field was under reduced-tillage (ridge till) on a silt loam soil and irrigated using a subsurface drip irrigation system. Evapotranspiration flux (ET m ) above the crop canopy was measured using a deluxe version of a Bowen ratio energy balance system (BREBS) and ET o was calculated with the Penman–Monteith method. The single-K c and dual-K c -estimated ET c values, both unadjusted for residue cover, were compared to ET m . The unadjusted FAO-56 K c values performed poorly as the single-K c underestimated ET m during the initial crop growth stage by 21% in 2007 and 33.6% in 2008 while the dual-K c overestimated ET m during the same growth stage by 16.8% in 2007 and 16.5% in 2008. Extended simulations were conducted to determine the magnitude by which ET c is reduced for each 10% of soil surface covered with crop residue. Downward adjustments in soil water evaporation (E s ) for every 10% of the soil surface covered with crop residue improved the accuracy of ET c estimated by the dual-K c method. The largest changes in ET c due to adjustments in E s occur during the initial stage of the growing season. The best estimates for seasonal ET c were obtained by reducing E s by 5% for every 10% of surface covered with residue in 2007 (R 2 =0.77, RMSD=0.87mmd −1 , E=0.94) and 2008 (R 2 =0.83, RMSD=0.84mmd −1 , E=0.95). Greater improvements in the accuracy of estimated seasonal ET c were obtained by reducing E s by 2.5% for each 10% of surface covered with residue during the initial stage and by 5% during the rest of the crop growth stage. These results suggest that the more computationally-involved dual-K c method with adjustments in E s for each 10% of surface covered with residue improves the prediction of ET c in fields with soil surface residue cover, especially during the initial growth stage. Inaccurate selection of percentage reduction in E s can result in substantial overestimation or underestimation of seasonal ET c by the dual-K c method.