Abstract
Encouraged by the necessity to better understand the water use in this woody crop, a study was carried out in a commercial drip-irrigated young almond orchard to quantify and monitor the crop evapotranspiration (ETc) and its partitioning into tree canopy transpiration (T) and soil evaporation (E), to list and analyze single and dual crop coefficients, and to extract relationships between them and the vegetation fractional cover (fc) and remote-sensing-derived vegetation indices (VIs). A Simplified Two-Source Energy Balance (STSEB) model was applied, and the results were compared to ground measurements from a flux tower. This study comprises three consecutive growing seasons from 2017 to 2019, corresponding to Years 2 to 4 after planting. Uncertainties lower than 50 W m−2 were obtained for all terms of the energy balance equation on an instantaneous scale, with average estimation errors of 0.06 mm h−1 and 0.6 mm d−1, for hourly and daily ETc, respectively. Water use for our young almond orchard resulted in average mid-season crop coefficient (Kc mid) values of 0.30, 0.33, and 0.45 for the 2017, 2018, and 2019 growing seasons, corresponding to fc mean values of 0.21, 0.35, and 0.39, respectively. Average daily evapotranspiration for the same periods resulted in 1.7, 2.1, and 3.2 mm d−1. The results entail the possibility of predicting the water use of any age almond orchards by monitoring its biophysical parameters.
Highlights
The relatively small size of the studied almond orchard field is a challenge since the footprint area contributing to the turbulent flux measurements must remain within the parcel limits, while a certain position over the canopy top is recommended to capture all eddies
K from NDVI and other vegetation indices [44,45] show a variety of functions for herbacb ceous crops,the butexperimental few can be found about almond treesorchards, and other orchards
Difficulty of measuring the transpiration of this complex cover that is partially bility approach, combined to radiometric temperature measurements, to capcovered, frequently under water-stress, and with part of the soil exposed to evaporation
Summary
The global planted area and production of almonds are steadily increasing. Spain ranks first in planted area with almonds in the world, with more than 650,000 ha, followed by the western United States of America (USA) with about 441,000 ha. The USA leads the production, accounting for 77% of the world crop share in 2019, whereas Spain only contributes a 6% of the share [2]. This is due to the low average yields obtained in our country as almond trees are mainly grown under rainfed conditions and on marginal soils in areas where annual rainfall ranges from 250 to 350 mm [3].
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