response of sugar beet to saline irrigation water in different growth stages

in order to study the effect of irrigation water salinity on quality and quantity of sugar beet (beta vulgaris) at four growth stages, an experiment was conducted in rudasht salinity and drainage research center from 2004-2006. in this experiment, 11 different water salinity treatments and three sugar beet cultivars (ic, 7233 & 7233-p29*msc2) were considered using split plot design based on randomized complete block design with four replications.the results showed that the increase in irrigation water salinity from 4 to 8 and from 8 to 12 ds/m ec caused significant reduction in root yield (ry), sugar yield (sy) and white sugar yield (wsy). the highest belonged to the check treatment. the least reduction in root yield and the highest response to salinity were observed at the 4th and first growth stages, respectively. irrigation with 8 ds/m ec of water had no significant effect on ry at the third and fourth growth stages, but at the first growth stage it significantly decreased ry .irrigation water with 12 ds/m ec had no significant effect on ry at fourth growth stage, but at the other growth stages significantly decreased ry. irrigation with 8 and 12 ds/m ec decreased ry about 24, 33 percent as compared to the check at all growth stages, respectively.  by increasing the irrigation water salinity from 8 to 12 ds/m, ry was dramatically decreased from the second growth stage afterwards. it can be concludedthat the first and second growth stages have the highest sensitivity to salinity and that the increased soil salinity results in increased sensitivity of sugar beet to salinity.