Analyses of spring barley evapotranspiration rates based on gradient measurements and dual crop coefficient model

Abstract

The yield of agricultural crops depends on water availability to a great extent. According some projections, the likelihood of stress caused by drought is increasing in future climates expected for the Central Europe. Therefore, in order to manage agro-ecosystems properly, it is necessary to know water demand of particular crops as precisely as possible. Evapotranspiration (ET) is the main part of water balance which takes the water from agro-ecosystems away. The ET consists of evaporation from the soil (E) and transpiration (T) through the stomata of plants. In this study, we investigated ET of spring barley 1-ha field (Domaninek, Czech Republic) measured by Bowen ratio/energy balance method during growing period 2013 (May 8 to July 31). Special focus was dedicated to comparison of barley ET with the reference grass ETo calculated according FAO-56 model, i.e. the determination of barley crop coefficient (Kc). This crop coefficient was subsequently separated into soil evaporation (Ke) and transpiration fraction (Kcb) by adjusting soil and phenological parameters of dual crop coefficient model to minimize the root mean square error between measured and modelled ET. The resulting Kcb of barley was 0.98 during mid-growing period and 0.05 during initial and end periods. According to FAO-56, typical values are 1.10 and 0.15 for Kcb mid and Kcb end, respectively. Modelled and measured ET show satisfactory agreement with root mean square error equal 0.41 mm. Based on the sums of ET and E for the whole growing season of the spring barley, ET partitioning by FAO-56 dual crop coefficient model resulted in E/ET ratio being 0.24.