Simulating Basil Response to Irrigation Water Salinity

Several mathematical models exist that represent plant response to salinity. These models consider salinity of the soil saturation extract (ECe) for plant response to salinity in the root zone. A considerable step would be taken towards applying such models, if irrigation water salinity can be used instead of ECe, because under field conditions, irrigation water salinity measurement is much easier than determining soil salinity. The objectives of this study were to quantify basil response to irrigation water salinity, to estimate its yield salinity threshold value and to investigate efficiency of available mathematical models for estimating its yield based on irrigation water salinity. Consequently, a large experiment was conducted with 13 water salinity levels including 1.175 (control treatment), 1.8, 2, 2.2, 2.5, 2.8, 3, 3.5, 4, 5, 6, 8, and 10 dSm^-1. The designated salinity treatments were performed by diluting the Shoor River saline water with adequate quantity of fresh water. In order to quantify the salinity effect on basil yield, seven mathematical models were selected. The results indicated that basil yield reduction threshold value based on irrigation water salinity was 1.7 dSm^-1 with yield reduction gradient of 8.1% per dSm^-1. The mathematical model of Homaee et al. (2002) provided more accuracy than the other models in simulating basil yield reduction function based on irrigation water salinity. Overall, the results of this research indicated that root water uptake models of Homaee et al. (2002), van Genuchten and Hoffman (1984) and two statistical models of Steppuhn et al. (2005) provide reasonable results for simulating basil yield response to irrigation water salinity, respectively (the least nRMSE and ME). The results further indicated that when enough leaching was applied, there would not be significant differences between the ECe-based models and those obtained based on irrigation water salinity.