Effect of changing irrigation system from surface (flooding) to subsurface method with PVC pipes on soil salinity, growth and yield of pistachio trees

In this project, the possibilities of changing the method of surface irrigation (flooding) to subsurface irrigation system (with porous PVC tubes) were studied on mature pistachio trees. This research was conducted as a randomized complete block design with three treatments and three replications. Treatments included: control (S) by flood  irrigation with 48 days irrigation frequency and the volume of 6720 cubic meters per hectare, P1 treatment, subsurface irrigation with PVC pipes with the amount of water used for irrigation control(S) and 12 days irrigation frequency and, P2 treatment, subsurface irrigation with PVC pipes with a water content of 75% of the water used to control and 24 days irrigation frequency. The results showed that among the growth characteristics, leaf area, total number of buds, percentage of fallen bud and vegetative bud were significantly affected by changes in irrigation methods. But changing irrigation methods on the most of quantitative and qualitative factors, significant effect at 5% level, as, increased the dry product from 0.8 to 1.6 Kg per tree, reduced blanking from 1.7 to 4.25 percent, increased splitting from 3.5 to 6 percent and reduced the number of nuts per ounce of pistachios from 1.3 to 2 units. While the WUP in irrigation methods of P1 and P2, increased 41.4% and 61.6%, respectively. There were no significant differences (P≤ 0.05) in subsurface irrigation treatments in most traits. The results of soil salinity in the root zone of trees in autumn (before leaching) also showed an increase in soil salinity in the soil surface and above the subsurface pipes. But, soil salinity after leaching and precipitation in the winter was appropriately (Less than 9 dS/m). Economic evaluation of this project showed that high economic justification. So, with an annual investment of about 60 million rials (as an initial investments) in Hectare to change the system, depending on the choice of irrigation method P1 or P2, respectively, earning between 7.6 to 15.2 times the initial investments, growers will receive. Therefore, considering the limitations of the pistachio producing regions in Iran, In terms of quantity and quality of available water resources, P2 method, due to a 25 percent reduction in water consumption and increasing 61.6% and 14.3% in WUP, respectively, compared to methods S and P1, is advisable.