The use of spectral vegetation indexes requires an experimental background. In this study field trials were conducted during 2004 and 2005 on sugar beet. Seven different irrigation treatments were applied. During the experiments soil water status, spectral reflectance, leaf area, plant dry weight and yield were observed and recorded. Water and yield relationships were determined and water use efficiency (WUE) was calculated. The relationships between spectral vegetation indexes and agronomic parameters were determined. According to the results, excessive irrigation does not increase yield and when nearly 500 mm water is used, maximum WUE is 7.2 kg m(-3). The highest determination coefficients were calculated between LAI and simple ratio (SR, R-2 = 0.59), sugar beet yield and soil adjusted vegetation index (SAVI, R-2 = 0.91). Consequently, spectral indexes, which can be calculated from data obtained through either handheld spectroradiometers or satellites, could prove useful tools for agricultural monitoring and management. Copyright (C) 2010 John Wiley & Sons, Ltd.