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AGROCLIMATOLOGY

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

^a 3 Avenue Cadi Ayad, Résidence Bekkouri, Apt. No. 13, 90000 Tangier, Morocco
^b Faculty of Horticulture, Minami Kyushu Univ., 11609 Minami Takanabe, Takanabe-cho, Miyazaki 884-0003, Japan
^c Agric. Engineering Res. Inst. (AERI), P.O. Box 31585, Karaj, Iran
^d Arid Land Research Center, Tottori Univ., 1390 Hamasaka, Tottori 680-0001, Japan
^e Faculty of Engineering, Kyushu Kyoritsu Univ., 1-8 Jiyugaoka Yahata-nishi-ku, Kitakyushu 807-8585, Japan

^* Corresponding author (zeggaf.adel{at}yahoo.co.uk).

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.

Abbreviations: BREB, Bowen Ratio Energy Balance • E, latent heat flux • E_c, flux of latent heat from the maize transpiration • DAE, days after emergence • E_s, soil evaporation • E_s, soil surface latent heat flux • ET, evapotranspiraton • ETo, reference evapotranspiration • G, soil heat flux • H, heat flux • H_c, flux of sensible heat from maize transpiration • H_s, sensible heat flux from soil surface • LAI, leaf area index • L_v, latent heat of vaporization • R_n, net radiation • R_ns, net radiation reaching the soil surface • T, canopy transpiraton • T_air, air temperature • u, wind speed

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Received for publication June 6, 2007.