Yield response of fennel (Foeniculum vulgare Mill.) to irrigation with saline water

Salinity causes yield reductions if threshold levels are exceeded, while it can cause the deterioration of some qualitative parameters and/or the improvement of others. Two years (2000-2001, 2006-2007) research was carried out to evaluate the effect of water quality on yield and quality of fennel, a vegetable very common in Apulia region. We compared two types of soil and two sodium absorption ratio of irrigation water obtained by dissolving in distilled water NaCl + CaCl2 (1:1) or only NaCl, and four electrical conductivity of water of 0.7 (control), 4, 8 and 12 dS m(-1). The soil type does not show any noticeable effect on the tested parameters. The salt type influenced the plant development and the total soluble solids contained in the bulbs. The plant height, the leaf and the bulb weight were, respectively, 6, 11 and 21% higher in NaCl + CaCl2 treatment as compared to NaCl one. The plant height, the leaf and the bulb weight dropped, respectively, by 33, 49 and 71%, shifting from 0.7 to 12 dS m(-1) salinity treatments. The dry matter content and total soluble solids increased with rising salinity. In fact, shifting from the control to the more saline treatment, the leaves and the bulbs dry matter increased, respectively, by 15 and 13%, and total soluble solids increased by 17%. Moreover, the increase in salinity favoured the production of flattened bulbs. The application of the Maas and Hoffman model to salinity response confirms the ranking of this species among moderately salt sensitive species, even though the critical threshold was the same for NaCl and NaCl + CaCl2 treatments (1.26 dS m(-1)), while the slope was higher in NaCl treatment (14.24% m dS(-1)) than NaCl + CaCl2 (10.39% m dS(-1))