The Values of Crop Coefficients and Bowen Ratio of Field Crops in Areas with Insufficient Precipitation in Central Europe

The aim of this study, based on measurements of actual evapotranspiration of vegetation, was to determine the values of the crop coefficient ( K c ) for selected crops and the effect of growth on the dissipation of radiation energy. The actual evapotranspiration (ET a , mm day −1 ) of Beta vulgaris , Hordeum vulgare , Medicago sativa , Sorghum bicolor , Triticum aestivum and Zea mays were measured under field conditions during 2007–2012 by the Bowen ratio energy balance (BREB) method. The values of potential evapotranspiration (ET 0 , mm day −1 ) and the dynamics of the above‐ground dry biomass production and values of the water productivity (WP, g H 2 O kg −1 ) were estimated. In the cereals, up to the onset of the ripening stage, the typical values of β (Bowen ratio) had exceeded 1.0. Crops such as M. sativa , B. vulgaris , S. bicolor and Z. mays had contributed significantly more to the elimination of heating of the atmosphere than cereals. In the cereals ( H. vulgare and T. aestivum ) the K c values varied around 1.0 up to the onset of the ripening phase. Thereafter the K c values decreased to 0.5. Higher values of WP compared with H. vulgare and T. aestivum were indicated by Z. mays and S. bicolor stands.