Effect of Nitrogen and Weed Interference on the Quality and Quantity of Sugar Beet (Beta vulgaris L.)

In order to determine the effect of weeds interference and nitrogen on the sugar beet growth and yield, a field study was performed in the 2010 growing season as a split plot design based on RCBD with three replications in Hana region (Semirom, Esfahan). Treatments were four levels of nitrogen from urea source as the main factor (0, 70, 150 and 210 kg ha-1) and weed interference at five levels (6-leaf, 8-leaf, 10-leaf, 12-leaf, and throughout the growth stages) growth stages in sugar beet as the sub factor. The results indicated that nitrogen and weed interaction had significant effects on the quantitative and qualitative traits of sugar beet (root yield and sugar). With increasing the nitrogen levels from 150 to 210 kg ha-1, the percentages of sugar molasses, sodium, and α-amino nitrogen were increased by 7.48, 24.26 and 21.09%, respectively, while the impurity percentage of sugar, alkalinity coefficient, and extractable sugar content were reduced by 3.09, 8.18, and 4.78% , respectively. The highest  total fresh weight, root fresh weight, root dry weight, total biomass and  root yield (2.1, 2.18, 1.55, 1.73 and 1.33-times, respectively) were achieved under high levels of nitrogen (210 kg ha-1) and weed interference at the 6-leaf growth of sugar beet in comparison to the use of  no nitrogen. Reduced duration of weed competition and /or weed free till 6- leaf growth stage of sugar beet along with application of 150 kg ha-1 N led to reduction in weed interference, detrimental effect of nitrogen on quality characteristics, and increase in the root yield of sugar beet.