Studying the effect of different planting and harvesting dates on the quantitative and qualitative yield of sugar beet under transplanting conditions

Introduction
Sugar beet (Beta vulgaris) is  one of the main sources of sugar production after sugarcane (Saccharum officinarum). The planting date is one of the most important factors affecting the yield and quality of sugarbeet. Achieving appropriate economic  yield  in sugar beet depends on proper vegetative growth during the early growth season and the correct allocation and distribution of photosynthetic assimilates. Shortening the plant growth period can be achieved under controlled conditions by planting seedlings in a nursery and transplanting them to the main field at the appropriate time, thereby reducing the risks associated with late winter cold and water shortage. Under transplanting conditions, sugar beet root yield has been reported to increase compared with direct seeding at the same sowing date. Another important factor influencing the economic yield of sugar beet is the determination of an appropriate harvesting time. Since sugar beet, unlike cereals, does not have a specific physiological maturity stage, identifying the optimum harvest time plays a vital role in final productivity. The harvesting time of sugar beet in each region depends on climatic conditions and the ability to achieve maximum white sugar yield. Given the importance of sugar beet planting in West Azerbaijan province and the role of planting and harvesting dates in determining final yield, the aim of this study was to investigate the effects of planting and harvesting dates on the quantitative and qualitative characteristics of sugar beet under transplanting and direct seed conditions.
Materials and Methods
This study was carried out in Miandoab County during the 2023 growing season as a split-plot experiment based on a randomized complete block design with four replications. Three planting dates (Febuary 28, March 20, and March 29) and three harvesting times (Julay 6, August 6, and October 7) were allocated to main plots and sub plots, respectively. The cultivar used in this experiment was Novodoro. For transplanting,  seedlings were produced in a nursery prior to the main field planting date. When the average seedling root diameter reached 3.5– 4 cm, the seedlings were irrigated and defoliated. Transplanting to the main field was carried out within less than one day. Planting was carried out manually at 20 day intervals, with a plant spacing of 20 cm. The first irrigation was applied immediately after transplanting. After harvesting, root weight and pulp samples were taken at each harvest date. Quantitative and qualitative traits including root yield (RY), sugar content (SC), white sugar content (WSC), sugar yield (SY), white sugar yield (WSY), sodium (Na), potassium (K) and α-amino nitrogen as root impurities, alcality (Alc), extraction coefficient of sugar (ECS) and molasses sugar (MS) were measured. Data analysis was performed using SAS software (Ver. 9.1) and mean comparisons were conducted  using  Duncan’s multiple range test.
Results and Discussion
Analysis of variance (ANOVA) showed that the effect of planting date as the main factor was significant for all traits at the 0.01 probability level. The effect of harvest date was significant for molasses sugar content at the 0.05 level and significant for all other triats at the 0.01 level. The interaction between planting date and harvest date was also significant for all traits at the 0.01 probability level, indicating the combined importance of these two factors in determining quantitative and qualitative yield. Mean comparison of the interaction effects showed that planting on March 20 and harvesting on October 7 resulted in the highest root yield (85.57 t ha^-1). In all planting dates, root yield increases with delayed harvesting. Moreover, across all harvesting dates, the highest root yield was obtained from March 20 planting date. The increase in root yield under early planting and transplanting conditions is likely due to improved vegetative growth, greater leaf area development, enhanced energy absorption, and increased production and translocation of photosynthetic assimilates to the roots. The highest sugar content (16.25%) was observed in plots planted on March 20, and harvested on August 6, whereas the lowest sugar content (7.30%) was recorded in directly seeded plants planted on March 29 and harvested on October 7. Delaying harvest from July 6 to October 7 significantly increased sugar yield at all planting dates. In addition, the highest sugar yield across all harvest dates was obtained from the March 20 planting date.
Conclusion
Since white sugar yield is the most important economic trait in sugar beet, conclusions were drawn primarily based on this parameter. The maximum white sugar yield was achieved in treatments planted on March 20 under transplanting conditions and harvested on August 6 and October 7. These treatments showed a significant advantage over other planting dates, particularly direct seeding. It can be concluded that these treatments optimally utilized environmental factors such as light and temperature, leading to improved white sugar yield. Finally, the use of an early planting and harvesting system not only resulted in maximum economic yield but also reduced input consumption and provided sufficient time for field preparation for the subsequent crop.