Introducing a stratified vertical gravel tube subsurface drip system under different irrigation regimes for pistachio: Growth, yield and water productivity

Abstract

High evapotranspiration and low precipitation are known as the main challenging factors for pistachio (Pistacia vera L.) orchards situated in arid and semi-arid regions. Therefore, it is necessary to take some measures to mitigate surface evaporation. This study was carried out to assess water productivity (WP) as well as yield and annual shoot growth of pistachios using a new method of irrigation known as the stratified vertical gravel tube subsurface drip irrigation (SVGTSD) system in a 15-year-old pistachio orchard in an arid region in Iran. In this system, each tree contained four vertical gravel columns with different lengths. A randomized complete block design with a split-plot arrangement with three replicates (five trees in each plot) for 3 years was used. Three irrigation regimes included 100% crop evapotranspiration (100% ET_c), 85% ET_c and 70% ET_c (as the main plots), and seven vertical gravel column with a depth arrangement of 40–40–40–40 cm (using a gravel column from the lateral pipe level and without a gravel tube as the control) and gravel-filled tubes with depths of 10–10–10–10 cm, 10–10–20–20 cm, 10–10–30–30 cm, 10–10–20–30 cm, 10–10–20–40 cm and 10–10–20–50 cm (all 30 cm below ground level) (as subplots) were used. The results showed that the different depths of gravel tube placement significantly affected the annual shoot growth and yield. The deeper the tube was placed, the greater the yield and annual shoot growth, resulting in 10–10–20–50 cm being the most productive. Regarding tree growth, yield and WP, the best performance was observed at full irrigation (100% ET_c) with a 10–10–20–50-cm vertical gravel tube arrangement. Furthermore, in this subsurface irrigation method, there was no concern regarding emitter clogging by roots, root accumulation around the emitters or root intrusion into the emitters. In addition, having a low additional cost (only 13.9%) in comparison with conventional subsurface drip irrigation together with a higher yield (3475 kg ha⁻¹), WP (0.9 kg m⁻³) and shoot growth (35 cm), SVGTSD is more economical and feasible compared to other irrigation methods and can be extensively applied in pistachio orchards.