POSSIBILITIES OF INFLUENCING THE FORMATIO N OF SUGAR-BEET YIELD BY BIOLOGICALLY-ACTIVE SUBSTANCES

In the years 1985 to 1994 in minimum three years' time sequence the ef fect of Rastim 30 DKV, Relan PGR, Atonik, Elnoh and cytokinins on the amount and quality of harvested sugar beet was studied and compared wi th an untreated control. The first spraying was carried out in the per iod when sugar beet had 6 to 14 leaves and began to set rows, i.e, in the growth stage 26 to 38. The second spraying was accomplished 4 to 6 weeks before harvest, i.e, in the growth stage 46. Cytokinin B and fi rst application of cytokinin B on average of three followed years (198 5 to 1987) raised the yield of white or digestion sugar by 5 to 6%, wh at is in close correlation with higher yield of tubers and balanced su gar content, raised content of ashes compared with untreated control. Relan PGR influenced on average of studied years (1986 to 1989) the su gar production by raised tuber yield and reduced alpha-aminonitrogen c ontent. Relan PGR on average of studied years increased white sugar yi eld by 7.2%. bn average, this is an increase in production by 0.3 to 0 .4 t sugar per 1 ha. The trials confirmed a positive influence of the first treatment on the leaf area production and later also on the grow th of tubers. Anticipated effect of the second treatment on higher dep osit of sugars into tubers. Preharvest application of Elnoh in the pha se 46 showed its effect on increase in sugar content. Sugar content on average of studied years (1986 to 1989) increased relatively by 2.3%, what represents in absolute value an increase in sugar content from 1 5.86 to 16.23%. Tuber yield on the level of control and increased suga r content had a positive influence on the yield of white sugar which r aised by 4.2%. Two treatments by Rastim 30 DKV carried out on average of studied years (1988 to 1992) increased per hectare tuber yield by 5 .0%, did not influence sugar content on average of studied five years. This increased white sugar yield by 3.6%, what is an increase by 240 kg sugar per 1 ha. In the years 1988 to 1994 the effect of two Atonik applications was followed, on average of studied years it increased tu ber yield by 2.3%. There were insignificant tendencies in increase of sugar content, decrease in alpha-aminonitrogen content. In total Atoni k increased white sugar yield by 2.4% on average of studied years. Gen erally, our results are in congruency with conclusions from literature (Henselova et al., 1989, 1993; Rozkosova, 1993; Zahradnicek, 1993 and others) but on average of studied experimental years they do not atta in a significant positive effect.