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

In the years 1985 to 1994 in minimum three years' time sequence the effect of Rastim 30 DKV, Relan PGR, Atonik, Elnoh and cytokinins on the amount and quality of harvested sugar beet was studied and compared with an untreated control. The first spraying was carried out in the period 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 first application of cytokinin B on average of three followed years (1985 to 1987) raised the yield of white or digestion sugar by 5 to 6%, what is in close correlation with higher yield of tubers and balanced sugar content, raised content of ashes compared with untreated control. Relan PGR influenced on average of studied years (1986 to 1989) the sugar production by raised tuber yield and reduced alpha-aminonitrogen content. Relan PGR on average of studied years increased white sugar yield 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 growth of tubers. Anticipated effect of the second treatment on higher deposit of sugars into tubers. Preharvest application of Elnoh in the phase 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 15.86 to 16.23%. Tuber yield on the level of control and increased sugar content had a positive influence on the yield of white sugar which raised 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 tuber yield by 2.3%. There were insignificant tendencies in increase of sugar content, decrease in alpha-aminonitrogen content. In total Atonik increased white sugar yield by 2.4% on average of studied years. Generally, 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 attain a significant positive effect.