Irrigation scheduling in processing tomato crop cultivated in Southern Italy: the role of physiological parameters.

Processing tomato, a largely cultivated crop in Mediterranean area, is a spring-summer crop sensitive to water stress. Its seasonal water requirement is estimated around 500-600 mm, almost totally supplied by irrigation. Unfortunately, water resources for agricultural use, in arid and semi-arid Mediterranean regions, like Southern Italy, are quickly reducing both for the higher request by civil and industrial sectors and the climatic changes which cause air temperature increase and irregular rainfall distribution. So for tomato crop, in order to protect water resources is necessary a suitable irrigation management strategy by using a correct irrigation scheduling, usually based on: “soil water measurements”, “soil water balance calculations” and “plant-based measures”. Plant-based measures, as leaf water potential, osmotic potential and crop canopy temperature (used for “Crop Water Stress Index” calculation – CWSI –) may give interesting informations about the correct irrigation scheduling. The aim of this study is to obtain indications about irrigation scheduling in processing tomato through the evaluation of leaf water potential, osmotic potential and CWSI values. Therefore, a field trial was carried out in Foggia (Southern Italy: 41°46’ N and 15°54’ E) on four tomato hybrids (Ercole, Genius, Tania and Ulisse) irrigated with three different water regimes (restoration of 100%, 75% and 50% of maximum crop evapotranspiration). In the critical stage, from the beginning of the flowering to the beginning of the fruit color breaking, before irrigations, leaf water potential, osmotic potential and crop canopy temperature were measured. Crop canopy temperature was used for CWSI calculation. At harvest time, beside several quanti-qualitative parameters, marketable fruit yield was taken and used for the “Water Use Efficiency” (WUE) calculation. Results show interesting considerations about the correct irrigation time in processing tomato through the use of physiological indicators. In our environmental conditions, physiological indicator values present a relation with marketable fruit yield in all sampling dates; neverthless, in one of this dates, physiological indicator values show a higher relation than other dates demonstrating in that period the highest effect of water stress on crop productivity. Moreover, a different physological response of hybrids has been obtained in function of sampling dates and water regimes.