Yield and quality of carrot as affected by soil salinity from long-term irrigation with saline water

In 1995 and 1996 the effects of the residual soil salinity on yield and some aspects of yield quality were studied in carrot (Daucus carota L.) grown during irrigation-free seasons on a field which had undergone the same irrigation treatments with saline water (0, 0.125, 0.25, 0.5 and 1% of commercial NaCl) since 1988. Within the range of electrical conductivity of the saturated-soil extract (ECe) between 1.9 dS m(-1) (treatment 0%) and 4.2 dS m(-1) (treatment 1%) the marketable yield decreased by about 65% and the (-2) by 57%. The N concentration was increased from 2.53 to marketable root number m(-2) 3.32 g 100 g(-1) d.m. (leaf) and from 1.28 to 1.47 (root) to increased soil salinity. Na and Cl concentrations of leaf and root were doubled in plants grown on soil with the highest salinity. Root characteristics and mineral composition of leaves and roots were significantly affected in plants grown on salt-affected plots with a different partioning of ions in plant tissues. The response of salt tolerance was evaluated by using the Maas and Hoffman "threshold slope" model. The threshold value was 2.0 dS m(-1) and yield was reduced at the rate of 28% per unit increase in soil salinity. The rate of yield reduction was higher than those reported in literature for sensitive crops, due to the greater effects of soil physical and chemical conditions altered by long term irrigation with saline water: the soil of 1% treatment assumed typical characteristics of alkaline-saline soil.