Irrigation Management Based on PAW and IWC and Its Effect on Soil Salinity Distribution and Root Water Uptake

Plant Available Water (PAW) is the most common criteria for Soil Available Water (SAW) to plants which assumes uniform water availability between two matric potential limits (field capacity to permanent wilting point) and ignore other limiting factors for plants. Integral Water Capacity (IWC) is one of the most recently developed criteria for SAW that consider all soil restrictions including unsufficient aeration, rapid drainage, resistance of root penetrability and salinity, in order to estimate the SAW properly. In this study, in order to compare the applicability of PAW and IWC criteria in irrigation management, soil physical and hydraulical properties of a pistachio garden, with drip irrigation system, were measured and PAW and IWC ​​were calculated. Based on these criteria, two irrigation regimes ( and) were determined. According to the results, the irrigation periods for  and were 8 and 12 days and irrigation duration were obtained 6 and 12 hours, respectively. Soil salinity distribution and root water uptake in two irrigation regimes were simulated using HYDRUS-2D model after validation for garden condition which showed a high accuracy for modeling. The results showed that in , soil salinity is driven to areas farther from the root of the tree and the area with low salinity levels, which plays an effective role in water absorption, are expanded. Based on the simulation, 63.7% and 48.1% of crop water requirement were provided through  and  managements, respectively. Therefore, by using IWC index, irrigation management could have a better accommodation to field conditions and leads to less water and salinity stress.