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Effects of sowing date on plant establishment and bolting and the influence of these factors on yields of sugar beet

This study examined the effect of early sowing of sugar beet on plant establishment, bolting and yield and whether or not the standard of establishment and degree of bolting determined the most appropriate harvesting sequence. At Arthur Rickwood Experimental Husbandry Farm four experiments were made between 1974 and 1978 testing four sowing dates of four varieties each harvested on three occasions during the autumn. At Broom's Barn three dates of sowing of two varieties were tested in three experiments between 1976 and 1978. Sowing dates throughout the experiments covered a range from late February to late April. Also, at Broom's Barn in 1977 there were many bolters (plants which have a tall, flower-bearing stem) where the crop was sown on 4 March. The effects of bolter-control treatments, either cutting down the inflorescence or removing the plant, on sugar yield were compared. Sowing before mid-March often resulted in very gappy crops and many bolters; in consequence yields were seriously reduced. Late-March sowings were almost free from plant establishment problems and, where the bolting-resistant variety ‘Nomo’ was used, bolters were few; yields of Nomo were greater than where sown in early April. Progressively more yield was lost by delaying sowing throughout April. Variation in the extent of bolting between sites, seasons and sowing-date treatments was accounted for by variation in the number of cool days (with a maximum temperature of less than 12 °C) after sowing. Yield was lost at a rate of 0·7% for every 1% of bolters over the range 5–40% bolting. During the autumn, crops at Arthur Rickwood which had more than 5% bolters and/or less than 60000 plants/ha gained 0·45 t/ha less sugar than did those with full, bolterfree plant stands. In 1977 many of the early-sown plants bolted; pulling the bolters or cutting the inflorescences improved yield, but not sufficiently to raise yields to the level produced by later-sown, bolter-free crops.