Irrigation Water Use Efficiency and Yield of Pistachio under Aerated Subsurface Drip Irrigation System

Improving yield and Irrigation Water Use Efficiency (IWUE) is important for pistachio cultivation in Iran. Subsurface Drip Irrigation (SDI) is a novel irrigation system that is used by pistachio farmers. Oxygen deficiency could occur in the soil under crops irrigated by SDI, especially in heavy clay soils, due to creation of sustained wetting fronts around emitters. The focus of this work was to evaluate aerated water irrigation (oxygation) under SDI to overcome hypoxia in saline loam silt soil environments on 15 years old pistachio trees in desert climate. Two treatments including F3 (irrigation frequency once every 3 days without air injection) and F3-oxygation (irrigation frequency once every 3 days by air injection) were investigated in two years. The injection of 18% by volume air into irrigation water by SDI resulted in a beneficial effect on yield and IWUE in the second year of experiment; with yield values of 4.9 ton ha-1 for F3-oxygation against 4.4 ton ha-1 for F3; and IWUE values of 4.2 kg ha-1 mm-1 for F3-oxygation against 3.7 kg ha-1 mm-1 for F3. Decreases in yield and IWUE in the F3-oxygation in comparison with F3 were 33.3 and 28.2% in the first year, respectively; but yield and IWUE due to F3-oxygation were 11.1 and 13.5% greater in the second year compared to F3, respectively. At the end of the irrigation season, the nitrogen content of the nuts removal in F3, and F3-oxygation were 1.9 and 2.1% in the first year and 1.4 and 1.6% in the second year, respectively. The leaf K+ and nut Fe2+ concentrations in F3-oxygation were about 24 and 44% more than F3, respectively. Leaf area was larger in aeration treatment compared with the control. Overall, these results indicate positive effects of oxygated SDI system on pistachio trees and merit further investigation for improving yield and IWUE.