Estimation of actual evapotranspiration from vineyard by utilizing eddy correlation method

Evapotranspiration and heat flux measurements from orchards and row crops are notoriously difficult to make, since none of the more conventional procedures lend themselves to application over such rough and non-uniform surfaces (Hicks, 1973). Throughout such a heterogeneous region, differential heating within alternating rows of grapevines and bare soil, adds to the complexity of modeling the soil-plant-atmosphere system. In the present study, we used a simple numerical model to predict evapotranspiration over a vineyard. The model is used to determine the amount and timing of irrigation. The model consists of soil, vegetation and air layers. To each of these layers energy and mass balance equations are applied. A field experiment, in which we measured crop, soil and meteorological parameters, was carried out in a typical commercial vineyard in Israel during three seasons. Meteorological variables including net and global radiation, wind speed and direction, air temperature and humidity, soil, latent and sensible heat fluxes were obtained. The last two were measured by three eddy correlation systems. The systems were mounted as follows: one above the middle of the row at fixed height, the second above the soil area between the vine rows and the latter above both the plants and soil area. Crop measurements consisted of plant water potential components, diurnal and seasonal trends of stomatal conductance and photosynthesis rate. We evaluated the Leaf Area Index (LAI) indirectly and directly with non-destructive and destructive methods, respectively. The results showed differences between sensible and latent heat fluxes, when comparing measurements above the vegetation and those above the soil between the rows, when the wind was parallel to the rows. When the wind direction was perpendicular to the vines, horizontally homogenous heat fluxes were observed.