the effect of deficit irrigation on the quality and quantity of sugar beet in miandoab region

sustainable agriculture for producing food is not possible without optimal use of water resources. because of the limitation of water resources, deficit irrigation would be essential to increase water productivity. in order to evaluate the effects of deficit irrigation on quality and quantity of sugar beet, an experiment was carried out in a farm in miandoab agricultural research station for 2 years(1999-2000). the experiment was conducted in a split–plot design on the basis of randomized complete blocks with three levels of irrigation (100%, 75% and 50%) and three irrigation intervals (7,10,14 days) in four replications. the analysis of two years results indicated that there was a significant difference at 1% level among deficit irrigation and root yield and sugar yield. deficit irrigation decreased root yield and sugar yield, but because of the positive effect of deficit irrigation on sugar beet quality, the rate of root yield decrease was more than the rate of sugar yield. d7s100 treatment (irrigation interval 7 days and full irrigation), providing 100% of water need of plant, produced the highest root yield (67.71 t/ha) but in d14550 treatment root yield decreased by 48.7 percent. the effects of deficit irrigation was more on longer irrigation intervals. the results also indicated that the 50 percent levels of irrigation resulted in less root yield and  sugar yield which may not be accepted by farmers, therefore it cannot be recommended. considering water productivity, and avoiding s50 treatment, treatment d10s75 is recommended for the region. with 28.9% reduction in water use, there was only 23.5% and 16.6% reduction in root  yield and sugar yield, respectively.