ISHS Acta Horticulturae 718: III International Symposium on Models for Plant Growth, Environmental Control and Farm Management in Protected Cultivation (HortiModel 2006)
MEASURING AND PREDICTING EVAPOTRANSPIRATION IN A BANANA SCREENHOUSE |
| Authors: | J. Tanny, S. Cohen, D. Elmowitz, H. Liu, A. Grava |
| Keywords: | eddy covariance, Penman-Monteith equation, latent heat flux, sensible heat flux, net radiation |
| Abstract:
One way to reduce crop water use is to protect crops by shading with screens or screenhouses, thus reducing the radiative heat load and wind speed which, in turn, reduce crop evapotranspiration. The present paper presents measurements and modelling of evapotranspiration in a commercial flat-roof screenhouse in which banana was grown. The screenhouse was a rectangle, 352 228 6 m high, made of a transparent, 15% shading screen. Banana cultivar ‘Grand Nain’ was planted in August 2004, cultivated on the soil and drip irrigated twice daily. An eddy covariance (EC) system was deployed within the screenhouse, 186 m south and 128 m east of its northwest corner to measure latent and sensible heat fluxes. This location allowed a minimum fetch of 100 m in all directions. Canopy height during the measurement period averaged 4.2 m and the eddy covariance system was installed at 5 m height. Near the EC system, a net radiometer was installed at 5.5 m height. Soil heat flux was measured by five soil heat flux plates installed at a depth of 0.08 m. To calculate soil heat storage, two thermocouples were installed above each plate at depths of 0.02 and 0.06 m. External meteorological conditions were measured by a standard meteorological station located outside the screenhouse, about 150 m east of the measuring point. Average total daily evapotranspiration for the 14 measurement days was 5.550.24 mm day-1 (²plusmn; 95% confidence interval). These results fit the grower’s data of 7-8 mm daily irrigation, which is about 70% of the irrigation applied in open banana fields in this region of the country. Potential evapotranspiration (PET) was predicted by the standard Penman-Monteith equation for well irrigated short grass for both external and internal climatic conditions. The ratio between daily measured LE and external predicted PETout averaged 0.65±0.03. This compares favourably with the 70% irrigation applied by the grower within the screenhouse as compared to open field. The ratio between daily measured LE and internal predicted PETint averaged 1.060.08. It is concluded that standard Penman-Monteith modelling is a useful tool for predicting evapotranspiration in these screenhouses. | |
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