Background and Objectives: Sugar beet is one of the important sources of sugar production; nearly 40% of the sugar produced in the world is obtained from sugar beet. Since thousands of years ago, beet sugar has been a valuable component in the human diet. Beet transplanting is one of the suitable solutions to achieve a uniform plant population, produce more crops, reduce weed competition, reduce the use of herbicides and invest in a longer growing season by closing the primary canopy. In terms of the effect of planting date on plant establishment, control of weeds, pests and diseases, harvest time and product quality, it is inevitable to know the most suitable planting date for each region in order to improve the quality and quantity of the product. During the investigation on three sugar beet planting dates (May 9, June 7, and July 13), it was ‎reported that the delay in planting caused a decrease in root yield and white sugar. Also, transplanting ‎increased root size and yield compared to direct cultivation (Karbalaei et al., 2012). In another ‎experiment, it has been reported that the roots were short and multi-branched and the sugar yield ‎was higher than direct cultivation (KazeminKhah, 2005). During a study on four sugar beet planting ‎dates (March 15 and 30 and April 15 and 30), it was reported that with the delay in planting, the ‎number of main and secondary stems in the plant, the height of the plant and the dry weight of the ‎whole plant decreased (Chegini et al., 2013). In sugar beet cultivation, the final product or sugar ‎depends on several factors. In this, sugar content and root yield are of particular importance. ‎Therefore, although direct cultivation is more suitable in terms of sugar content, the high production ‎of roots in transplanting makes it superior to direct cultivation in terms of sugar yield (Nasri et al., ‎‎2012b).‎ Considering that the selection of the appropriate planting date is one of the important factors in the cultivation of any crop based on regional conditions, this experiment aimed to compare transplanting and direct seeding in the usual and early planting dates in order to increase the yield of beet sugar under climatic conditions of Kermanshah.
Materials and Methods: This experiment was conducted to enhance sugar beet yield by transplanting at Research Farm, ‎Campus of Agriculture and Natural Resources, Razi University, Kermanshah during two years ‎‎(2015 and 2016). In 2015, the experiment was conducted as factorial based on randomized ‎complete block design with four replications. Factors were three planting methods (seeding, 4-‎week transplanting and 6-week transplanting) and two planting dates (early planting and ‎common planting date). In 2016, the experiment was a randomized complete block design with ‎three replications. The treatments included 6-week transplanting at early planting (superior ‎treatment in the first year) and seeding (control). Since the purpose of the experiment in the first ‎year was to investigate the possibility of transplanting the plant, the plants were kept until the ‎crown closure stage and then the dry weight of the aerial parts and the fresh weight of their roots ‎were measured. In the second year, when the possibility of transplanting the plant was proved, ‎the plants were harvested at the usual time of sugar beet delivery to the sugar factory in the ‎region. Each experimental plot consisted of five rows of four meters long with a distance of 75 ‎cm between ‎the two rows and the distance between the plants on the planting rows was 20 cm. ‎In the ripening ‎stage, four plants were selected from the middle rows of each plot to measure the ‎plant's ‎morphological traits (plant height, number of leaves, petiole length, leaf length and width). ‎In order to ‎measure other traits (fresh weight of leaves, fresh weight of petioles, wet weight of ‎aerial organs, dry ‎weight of leaves, dry weight of petioles and dry weight of aerial organs) the ‎plants were transferred to ‎the laboratory and weighed using a electronic scale with an accuracy of ‎‎0.001 grams. Traits related to ‎yield and yield components included wet root yield, dry root yield, ‎root length, root diameter, root ‎volume, crown length, crown diameter, sugar content, sugar ‎yield, plant harvest index, and sugar ‎harvest index. The data obtained from taking notes and ‎sampling the desired traits were analyzed with the help of SAS software version 2.9. To compare ‎the averages of each of the treatments, the LSD method was used at the 5% probability level.‎
Results: The mean comparison of the simple effect of planting method in the first year showed that the 6-week transplant (91%) had a higher survival rate than the 4-week transplant (50%). The mean comparison of interaction effect of planting method and planting date showed that the highest dry weight of petiole, leaf and aerial organs and leaf area was related to early 6-week transplanting. The mean comparison in the second year showed that transplanting increased stomatal conductance, chlorophyll b, total chlorophyll, leaf weight, fresh weight of aerial organs, dry weight of leaves and dry weight of aerial organs compared to seeding. Results of the experiment in the first year showed that the best treatment was early 6-week transplanting, which increased the dry matter of aerial organs, root yield, and leaf area compared to other treatments. According to the obtained results, it seems that with the increase in the age of the transplant, the plant has a higher ability to establish and optimally use environmental factors and has been able to make maximum use of environmental resources in earlier planting than the usual time planting. Biomass depends on the amount of absorbed radiation, which also depends on the leaf area. The high diameter of the root indicates the high efficiency of the underground part in the use of storage materials. In addition, another reason for the increase in root dry yield and the subsequent increase in sugar yield could be high stomatal conductance and chlorophyll in the transplanting method.
Conclusion: This experiment was carried out in order to compare planting and seeding in the normal and early planting date to increase the yield of beet sugar in the weather conditions of Kermanshah. The results of the experiment in the first year showed that the early 6-week transplanting treatment was the best, which increased the dry matter of aerial organs, root yield and leaf area compared to other treatments. According to the obtained results, it seems that with the increase in the age of the plant, it has a higher ability to establish and optimally use environmental factors, and it has been able to make maximum use of environmental resources in cultivation earlier than the usual time and increase the dry matter of aerial organs, root yield, leaf area and plant height. The results of the experiment in the second year showed that compared to seeding, transplanting caused an increase in fresh and dry weight of aerial organs, fresh and dry root yield, root diameter, crown height and crown diameter. Also, from the results of the second year, it seems that, despite the multi-branching of the roots, the high sugar yield can be a good reason to replace direct cultivation with transplanting cultivation. One of the limitations of this research is the way to choose the shape of the seedling pot for the research. If the selected pots are very deep, multi-rooting may not happen. Considering that transplanting reduces the consumption of inputs in agriculture and the most important input in the agricultural sector of arid and semi-arid regions is water, therefore, beet transplanting is a promising solution to deal with drought.