Pistachio Response to Water and Salinity Distribution in Surface andSubsurface Drip Irrigation Systems

In this study, soil water and salinity distribution in surface drip irrigation (DI) and subsurface drip irrigation (SDI) systems with saline water were investigated. Plant measurements were used to obtain water stress response function parameters that are needed for HYDRUS-2D modeling. The hm50 and EC50 parameters that are the 50% reduction of water extraction due to pressure head and salinity, were calculated 8925 cm and 29.7 dS/m, respectively. HYDRUS successfully simulates soil water and salinity distribution in pistachio trees root zone. The results showed that in the immediate vicinity of the emitter, the soil salinity varies in a relatively low range and salt accumulation was observed far from the emitters. Also HYDRUS calculates daily transpiration and root water uptake that they were significantly correlated with stomatal conductance and sap flow. Plant measurements and HYDRUS results show that roots water uptake in SDI significantly was more than DI. Therefore, using SDI, by decreasing surface evaporation and conducting appropriate water and salt distribution in root zone reduce water and salinity stress. Furthermore, results revealed that soil moisture reduction after five days from irrigation, lead to limitation in root water uptake. so, it is necessary to decrease irrigation period from that applied in the field.