Investigating the Feasibility of the Autumn Cultivation of Sugar beet (Beta vulgaris L.) in Marvdasht

IntroductionDrought, as well as water scarcity, are the main limiting factors in the arid and semi-arid regions of the world, such as Iran (Deihimfard & Rahimi Moghadam, 2015). Autumn cultivation can be a solution provided that the upcoming long and cold temperatures do not limit the sugar beet development. One of the limitations of autumn sugar beet cultivation is dealing with low temperatures in winter, which results in vernalization and flowering of sugar beet in the first year. The bolting will reduce economic yield by reducing root weight as well as reducing sugar content (Taleghani et al., 2015). Considering the long period from sugar beet sowing to harvest, this study aimed to: (i) detect the interactions between planting dates and cultivars for three harvest dates; and (ii) recommend the best sugar beet cultivar with the best performance for increasing the sugar yield in Marvdasht region. Materials and MethodsA split-split-plot field experiment with the randomized complete block design (RCBD) in three replicates was conducted in two agronomic years (2016-17 and 2017-18) in Marvdasht. Three sowing dates 16 September, 7 October, and 27 October) were assigned to the main plots, and two varieties (Giada and Levante) consisted of the sub-plots. Three harvest dates (1 May, 26 May, and 20 June) were also assigned to the sub-sub-plots. Basic plot size was 15 m2, with five rows, 6 m long, and row spacing of 0.5 m. The root yield (RY) was determined by measuring the weight of roots from three middle rows and recalculating it as ton/ha. Root samples were analyzed in the laboratory for sugar beet root quality testing at Sugar Beet Research Institute in Karaj. Sugar content (SC) was measured according to the polarimetric method. Sugar yield (SY) was calculated following the equitation: SY = RY × SC. Results and DiscussionThe statistical analysis showed that the two-factor interaction of sowing and harvest dates was significant on the root yield (alpha <0.01). The mean comparisons of the treatments showed that the lowest yield was obtained at the sowing date of 27th October and the harvest date of 1th May (32.95 ton/ha). On the other side, the highest yield (75.75 ton/ha) was acquired with the interaction of the 16th September sowing date and 20 June harvest date. Bolting did not occur with the second and third sowing dates while it happened with the first sowing date. Bolting percentage at the first sowing date was also affected by delays in harvesting dates. The interaction of sowing date × cultivar × harvesting date was significant on sugar content. The highest sugar content belonged to the sowing date of 7th October and harvesting date of 26th May in the Giada cultivar, and the lowest sugar content belonged to the Levante cultivar in the sowing date of 7th October and harvesting date of 1st May. In other words, sugar content is strongly affected by sowing and harvesting dates, so early planting and delaying harvesting until July will increase the sugar content significantly. Also, higher sugar content can be achieved by adjusting the planting and harvesting dates to minimize bolting (Taleghani et al., 2011). ConclusionDelayed sowing and early harvesting led to reductions in root yield, sugar content, and white sugar yield. The treatment with a sowing date of September 16 and a harvesting date of June 20 resulted in the highest root yield. Although this treatment also had a high bolting rate, the increased yield compensated for the reduction in sugar percentage, resulting in the highest overall sugar yield. However, considering both economic factors and final product outcomes, and given that sugar yield was not significantly different between the second and third harvesting dates, the sowing date of September 16, combined with a harvesting date of May 26, was identified as the most effective treatment for sugar production in Marvdasht.