THE IMPORTANCE OF INORGANIC NITROGEN IN S OIL IN SUGAR-BEET CULTIVATION UNDER IRRIGATIONS

The aim of the solution of reasearch task conducted on carbonaceous ch ernozem of the southern Slovakia was to study the relation between an amount of inorganic N (N(an)) in soil during the vegetation, dynamics of yield formation and formation of qualitative parameters of sugar be et under irrigations. N(an) comprised in soil, as well as the dynamics of yield formation of fresh and dry matters were determined in 15-day intervals. Manure was applied to sugar beet in the amount 40 t.ha-1 doses of N - 0, 70, 110, 150 and 190 kg.ha-1 + constant doses of P-45 kg.ha-1 and K-160 kg.ha-1. The closest relation between root yield, s ugar output per area unit was when presented parameters were assessed together with N(an) comprised in soil in the mid May, that is on May 2 0. For this reason, this N(an) amount in soil was considered as the ba se for expression of the whole number of relations. N(an) amount in so il up to the depth of 0.8 m in this date was fluctuating from 245 to 5 20 kg.ha-1. As far as mineralizing capacity of soil is concerned, this was changing in dependence on gradated N doses; while on long-time un fertilized soil 107 kg of N was available by mineralization, in the va riants where manure + N was applied for each 1 kg of N applied, 1.60 t o 2.50 kg.ha-1 N(an) was available, fertilizing intensifies significan tly mineralizing processes in soil. Sugar beet root yields in dependen ce on the amount of N(an) in soil were fluctuating from 73.22 to 84.68 t.ha-1. An increase in root yields represented 11.40 t.ha-1 (+ 21 %). The highest root was gained at 400 kg.ha-1 of N(an) to the depth 0.8 m. Crown yields at the end of the vegetation was fluctuating within 33 .27 and 46.29 t.ha-1; an increase by 12.73 t.ha-1 (+ 38 %). In this ca se the highest yield too was pined at the amount of N(an) in soil 400 kg.ha-1. Digestible sugar content in dependence on the above parameter was ranging at the harvest from 17.93 to 16.54 %, white sugar content from 14.92 to 12.84 % what represented decrease in white sugar conten t by 2.08 %; white sugar output was ranging from 10.52 to 10.91 t.ha-1 (+ 0.390 t.ha-1). It follows from the above-mentioned data that incre ase in N(an) amount in soil from 260 to 400 kg.ha-1 to the depth 0.8 m increased the sugar output only negligibly. While the decrease in dig estible and white sugar content was highly significantly negative this relation was insignificant in sugar production. Results indicated one important moment, that is on the soils pertinent in optimizing the ir rigated regime, it is possible to gain the sugar output exceeding 10 t .ha-1 even at the amount of N(an) in soil 260 kg.ha-1. Just low N dose s ranging from 0 to 80 kg.ha-1 are required to be applied in order to have such an amount of N(an) in soil.