Sugar beet is one of the important industrial crops in sugar production industry. Recently, Iranian farmers have encountered some challenges such as restricting government support and lack of water for irrigation. Therefore, sugar beet production has declined in recent years. In addition, lack of precision planting equipment, dependency on labour force in weed control and synchronizing sugar beet planting with irrigation of other crops such as cereals has increased problems for farmers. The appropriate sowing technique, optimum sowing date and application of acceptable varieties will solve these problems.
This experiment was conducted during 2017 in Mashhad and Shirvan stations. The experimental layout was factorial experimental design based on randomized complete block design. The factors in this experiment were sugar beet varieties (Anakonda and Dorotea), planting method (Transplanting and seed sowing) and sowing or transplanting date (5 May and 5 June). For transplanting treatments, the seed was planted into paper pots in tunnel house around 30 days before transplanting. The plots area was 15 m-2, had 6 rows (50 cm apart) with 5 m length. In seed sowing treatments, seeds were sown 10 cm apart, then in 4-6 leaf stage, the plants were manually thinned to a density of 100,000 plants ha-1 (20 cm apart). In transplanting treatments, seedlings were sown 20 cm apart. The plants harvested on 27 October in Mashhad and 29 October in Shirvan. After harvesting, the root and leaf were weighted. Then a sample from the root in each plot was selected and used to measured criteria sugar content, root impurities, molasses content, extractable sugar, sugar yield and extraction coefficient of sugar.
The results showed that root yield and sugar yield of sugar beet in Shirvan were higher than Mashhad. While the root impurities and molasses content in Mashhad were higher than Shirvan. The difference in soil and weather conditions could be one of the reasons for these differences between two areas. Transplanting treatments showed the highest root yield and leaf weight rather than direct sowing. Furthermore, the root impurities were highest in transplanting treatments. According to the reports, branched roots in transplanting roots would be higher than direct sowing and it can increase the root impurities. Based on this hypothesis, direct sowing of sugar beet increased the impure sugar and extractable sugar. According to the positive correlation between root yield and sugar yield, the highest sugar yield obtained from transplanting treatments. The results represented that delaying in sowing date increased the root impurities and molasses content. Therefore, the sugar yield in the second date of sowing or transplanting was less than first sowing date. The second sowing date increased the percentage of sodium, potassium and amino nitrogen, 26.29, 21.24, and 14.42, respectively. In addition, the second sowing date increased the molasses content compared to the first sowing date by 13.61%. Other studies also reported similar results. Some of the studies mentioned that decreasing the growth period can increase the root impurities in sugar beet. Different genotypes also showed different responses. The highest root yield and sugar yield and the lowest root impurities were related to Anakonda. The molasses content in Dorotea was 5.11% higher than Anakonda. Some of the studies expressed that different genotypes have different cell capacity to store the sugar. According to the evaluation of the interaction between different factors, the highest root yield (77.34 ton.ha-1) and sugar yield (9.848 ton.ha-1) were observed in transplanted sugar beet that planted in the first sowing date. There is a significant correlation between the extraction coefficient of sugar and root impurities content, this led to root impurities interfere with crystallization of sucrose and decreased the sugar extraction.
According to the results, transplanted sugar beet had more yield quantity and quality compared to seed sowing. Also, the second sowing date decreased the quality and quantity of sugar beet. In addition, planting of sugar beet in Shirvan condition was better than Mashhad condition. In general, it seems that the transplanted Anakonda on 5 May in both areas will be appropriate. However, making a decision, in this case, requires further evaluating such as economic aspects.