In order to study the effect of sowing date and plant density on some quantitative traits and yield of sugar beet genotypes a field experiment was carried out at Sugar beet Seed Production Research Station of Karaj in 2006. Treatments arranged in a split, split plot experiment based on completely randomized block design with four replications. The main factors were two sowing dates as 14 April and 24 May. Sub plot were four plant density including 50, 75, 100 and 125 thousand plants per hectare and the sub-sub plots three sugar beet hybrids(428, 7112, and DS4027). The results showed that the green leaf number, crown dry weight, root dry weight, petiole length and root yield in first sowing date increased compared to second one, so on the second sowing date yield decreased 24.3% relative to first sowing date. Most traits improved with increasing plant density, especially root yield increased until 100 thousand plant ha-1. The maximum crown dry weight obtained from combination of the first sowing date and DS4027 genotype. Although, amounts of most traits of DS4027 was higher than 428 genotype, but they had equal root yield. There were significantly positive correlation between root yield and crown dry matter, total dry matter and dry leaf number. The best treatment obtained from combination of the first sowing date, 100 thousand plants per hectare and DS4027 genotype, however it recommends that the experiment carry out at several places and years to obtain the best sowing date and density and stable genotype.
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