29. Plant Response to Saline-Water Irrigation in a Sicilian Vineyard

This chapter presents results of a 3-year field investigation in a vineyard located in Sicily (Mazara del Vallo, Trapani) within the framework of the Project “Evolution of cropping systems as affected by climate change” (CLIMESCO). Soil-plant responses to two saline irrigation waters were determined by measuring soil hydrological characteristics, soil salinity, crop transpiration and stomatal conductance in field plots of a Sicilian vineyard. The results proved that crop transpiration (T _r) and stomatal conductance (G _s) were significantly affected by soil salinity conditions, expressed by electrical conductivity of soil saturation extract (EC_e). Significant reductions in T _r and G _s were found in plants irrigated with water of EC_w = 1.6 dS m⁻¹ (L) compared to T _r and G _s values in plots irrigated with water EC_w = 0.6 dS m⁻¹ (R). Significantly higher crop water stress index (CWSI) values, indicating stronger stress conditions, were measured in the L treatment, relative to the R treatment. Validity of the linear relationship between relative yield and relative transpiration was confirmed. A value of 0.7 for the yield response factor (Ky) provided accurate prediction of yield reduction in years 2008 and 2009. Reductions due to soil salinity, calculated according to Maas and Hoffman equation, showed that under conditions of water and salinity stress, yield reduction due to salinity represented a percentage of the total yield reduction of up to 11% in the L plots and up to 3.5% in the R plots. The investigation also indicated that EC_e (1.5 dS m⁻¹) discriminated a different plant response to salinity, indirectly confirming the Maas threshold value for grapes. Under the irrigation conditions in the Sicilian vineyard, it is suggested to implement management strategies aimed at keeping soil salinity below this threshold value. This can be realized by using low-salinity irrigation water only or by alternating the two irrigation sources.