THE INFLUENCE OF SOWING DATE AND PLANT-DENSITY ON THE DECISION TO RESOW SUGAR-BEET

To provide quantitative support for the decision on whether or not a c rop of sugar beet (Beta vulgaris L.) has to be resown after poor estab lishment, the effect of plant density (2 to 9 plants per m2) on sugar yield was investigated in six experiments in two consecutive years on three sites in the north, south-west and central regions of the Nether lands. Sowing dates, seedbed preparation and sowing were varied to pro duce a situation in which the effect of resowing could be analysed. Pl ant density influenced sugar yield more in the trials in the north and south of the country than in the central region on reclaimed marine s oil. The effect of sowing date on sugar yield was analysed with a simu lation model based on temperature and intercepted radiation. Yield los s caused by a later sowing date can be estimated by multiplying the th ermal time between two sowing dates by a constant (1.31) that is the y ield loss in g sugar per m2 per degrees-C day. As plant stage of the f irst-sown crop is also strongly related to thermal time, the yield los s due to a later resow date may be estimated using the plant stage of the crop to be resown.