A Bowen Ratio Technique for Partitioning Energy Fluxes between Maize Transpiration and Soil Surface Evaporation

Abstract

A field experiment was conducted in 2005 at the experimental station of the Arid Land Research Center, Tottori University, Japan, for comparing latent heat fluxes from a maize (Zea mays L.) field, maize transpiration, and soil surface evaporation by two different methods. The Bowen ratio energy balance method (Method 1) was used to measure latent heat fluxes above the maize canopy as well as between the soil surface and the canopy at 0.5‐h time intervals. Then, latent heat flux from maize transpiration was calculated by the difference between that of the maize field and soil surface. In Method 2, a weighing lysimeter and sap flow gauges were used to measure latent heat fluxes from the maize field and maize transpiration, respectively, at 0.5‐h time intervals. Then, latent heat flux from the soil surface was calculated by the difference between that of the maize field and maize transpiration. The coefficient of determination between latent heat fluxes by the two methods was 0.72 from the maize field and 0.77 from the maize transpiration. However, results indicated a low correlation between the latent heat fluxes from the soil surface by the two methods (r2 = 0.36). On the average, the Bowen ratio energy balance method underestimated by 6% the latent heat flux measured by weighing lysimeter data and overestimated by 14% that obtained by sap flow data resulting in a 30% underestimation of the measured latent heat flux at the soil surface. At daily time intervals, results were improved with relative errors around 19 and 21% for the latent heat fluxes from the maize field and maize transpiration, respectively. Finally, this study showed that the use of Method 1 for partitioning evapotranspiration at maize field level is feasible. The use of this technique for irrigation management to improve water use efficiency at crop field level needs to be explored.