Determining suitable sowing date and harvesting time of winter beet in Moghan, Fars and Golestan regions

Developing winter planting of sugar beet is a major solution for meeting sugar demand of the country. Water deficit crisis in recent years, introduction of new bolting-resistant cultivars and incomplete nominal capacity of sugar factories in such regions as Mu an, Fas (Fars) and Shirvan (Northern Khorasan) has posed the development of winter sugar beet cultivation in semi-arid regions of Iran as a major strategy for partial meeting of the needs of sugar factories. Therefore, the present strip-plot study was carried out in three growing years of 2008-2011 (in Mu an and Golestan) and in two growing years of 2008-2010 in Fars on the basis of a Randomized Complete Block Design with four replications in order to examine the possibility of winter cultivation of sugar been in three regions of Iran: Mu an (Lat. 39 39 N., Long. 47 55 E., Alt. 31.9 m), Aq-qala in Golestan (Lat. 37 09 N., Long. 54 34 E., Alt. 10 m), and Darab in Fars (Lat. 28 47 N., Long. 54 17 E., Alt. 1098.2 m). The main plot was devoted to sowing date at three levels (September 23, October 12 and November 1) as the vertical plot and the factorial combination of four harvesting time (late-May, late-June, late-July and late-August) with three sugar beet cultivars (foreign bolting-tolerant cultivars, Iranian bolting semi- tolerant cultivar and bolting-sensitive cultivar) was considered as the horizontal plot. It was found that despite the bolting of the plants, autumn production of sugar beet in Mu an was more influenced by harvesting time than sowing date. The most appropriate autumn sugar beet harvesting time was late-June in this region. In order for this harvesting time to be possible, the sowing date must be adjusted to October 12 to November 1. Nonetheless, the impact of varying climatic conditions on bolting complicates its management at field level. In Golestan despite the possibility of yield loss with delayed sowing, the tolerant cultivars of winter sugar beet must be sown from October 12 to November 1 and the harvest must be done from late-June to late-July in order to minimize the bolting of plants. The great variations of sugar extraction coefficient in different years in this region show that the successful winter cultivation of sugar beet would mainly depend on climatic conditions of a certain year. In Darab region, despite the loss of yield with delayed sowing and because of the non-significant differences among cultivars tolerant and semi-tolerant to bolting, it is recommended to sow tolerant cultivars from September 23 to October 12 and semi-tolerant cultivar from October 12 to November 1 and to harvest them during late-June. However, bolting of the plants was affected by meteorological parameters in the study year in this region, too. The increase in mean minimum, maximum and average daily temperature resulted in significantly higher root and sugar yield of winter sugar beet. Also, the increase in mean day/night temperature difference resulted in slight increase in root yield and at the same time, greater increase in sugar yield. The increase in bolting had a linear relationship with the increase in total intercepted vernalization temperature (4-8 C) to 818 hours. The increase in stemming percentage resulted in significantly lower raw and white sugar yield by reducing root yield, sugar content as well as root impurities (including Na and K). However, higher bolting damaged the yield by reducing yield quality in tolerant cultivars, by reducing root yield and sugar content and increasing impurities in semi-tolerant cultivar and by reducing yield quality and increase root -amino content in sensitive cultivar. Keywords: Autumn cultivation, cultivar, Fars, Golestan, harvesting time, Mu an, sowing date, sugar beet.