Water Productivity and Yield Response Factor in Two Cultivars of Processing Tomato as Affected by Deficit Irrigation under Semi-Arid Climate Conditions

Processing tomato is a high water demanding crop, thus requiring irrigation throughout the growing season in arid and semiarid environments. In these areas, maximizing water productivity is more important than maximizing yield. The application of deficit irrigation (DI) strategies to this crop may greatly contribute to save irrigation water. A field experiment was carried out in 2003 in a typical semi-arid Mediterranean environment of Southern Italy, in order to assess the effects of DI upon water productivity in two cultivars of processing tomato ('Solerosso' and 'Season'). Four irrigation treatments were studied: no irrigation following plant establishment (V0); 100% (V100), 50% (V50) and 25% (V25) evapotranspiration (ETc) restoration up to fruit maturity. DI differently affected fruit yield of the two cultivars: 'Solerosso' produced considerably less under water deficit conditions, whilst 'Season' kept high yield levels in all DI regimes. Water productivity progressively increased with the decrease of the amount of water distributed, reaching its maximum under V0 water regime. Water use efficiency (WUE) was positively affected by DI in both cultivars, suggesting that the crop does not benefit from the water when total crop requirements are fulfilled for the whole season. WUE variation in response to DI was more evident in cv. 'Season', whose WUE in V50 was 60% greater than that calculated for V100. The yield response factor Ky, which indicates the level of tolerance of a crop to water deficit (the greater Ky the lower the tolerance), was higher in 'Solerosso' (0.728) compared to 'Season' (0.309). This reveals a greater tolerance of this last cultivar to water shortage. In this respect, Ky may be a valuable tool in varietal screening for water deficit tolerance and, thus, for deficit irrigation adaptability evaluation in processing tomato.