Daily and Seasonal Pistachio Evapotranspiration in Saline Condition: Comparison of Satellite-Based and Ground-Based Results

This study was conducted in 2015 to estimate pistachio (Pistacia vera L.) water use in Marvast region, central Iran. Daily and seasonal pistachio actual evapotranspiration (ETₐ) was first estimated by running the surface energy balance algorithm for land (SEBAL) model, using 12 Landsat 8 satellite images and other ancillary data. Finally, SEBAL estimates of daily and seasonal water use over three experimental sites of pistachio orchards were compared against ones based on performing water balance analysis for the top 150 cm of the soil layer. For this purpose, a simple funnel-shaped device was made and used to collect the beneath rootzone drainage water and determine the leaching fraction (LF) as well as deep percolation at three scattered points across the sub-sections of each experimental site. The results reveal that the LF varies from 0.16 to 0.34, leading to deep percolation from 95.0 to 334.0 mm of the irrigation water. Eventually, the differences between ground-based and SEBAL-based pistachio ETₐ were 11% (ranged from 5.7 to 14.0%) and 10% (ranged from 7.1 to 16.4%) for daily and seasonal time scales, respectively. Based on the obtained results, more than 60% of Marvast pistachio orchards have seasonal water use of 410.0 to 680.0 mm (with the average of 594.3 mm), while the cumulative ETₒ and cumulative pistachio ETc of the same period were 1558.0 mm and 920.0 mm, respectively. In other words, Marvast pistachio trees extract less water from the soil compared with their potential water demands. This is due to the effect of salinity on reducing evapotranspiration rate as well as deficit irrigation of pistachio trees in the water scarce area of Marvast region. In any case, the difference between pistachio ETc and ETₐ is reflected in declination of the pistachio yield.