| Popis: |
The water footprint of a crop is the volume of water that is necessary to produce, therefore relating crop water requirements and yield. The components of water footprint, blue, green and grey water footprints refer to the volumes of respectively, surface and groundwater, rainfall, and water required to assimilate pollution, which are used to produce the crop yield. Determining blue and green water footprints is generally achieved using estimates of evapotranspiration. In the present study we have used evapotranspiration measurements to estimate the water footprint of a super-intensive olive grove in southern Portugal. Crop water requirements were measured using a sap flow technique, to determine transpiration and the eddy covariance method for direct measurement of evapotranspiration. This technique was used for a short period, while the sap flow measurements were performed for long periods, hence allowing the extension of the data series. Evapotranspiration measured directly was in average close to 3 mm d-1 and the ratio of actual evapotranspiration to reference evapotranspiration approached 0.6 for the same period. The water footprint of the olive crop under study was lower than those reported in literature. A possible reason relates to the density of plantation, yield and irrigation management. The irrigated grove under study produced a high yield, which compensates for high water use, leading to a water footprint lower than for rainfed or less dense groves. Furthermore, as evapotranspiration measurements were used to calculate water footprint instead of the common procedure, this might have also caused some differences. As recently discussed in literature, remote sensing techniques can provide estimates of actual evapotranspiration and water balance terms when associated with modeling. For the present study, water footprint estimates using in situ evapotranspiration measurements were further compared with water footprint estimates obtained with remote sensing. |
