The paper presents the findings of 6-year (1993–1998) investigations obtained in the field static experiment continued since 1967. This experiment concerned the estimation of the crop yield and its structure, and root technological quality under the conditions of crop rotation and extreme shortening of the rotation, i.e. monoculture. Investigations have proved that under agroclimatic conditions of north-eastern Poland it is possible to obtain 60 t of roots per ha in a naturally

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... t crop rotation, while in a long-term monoculture – 33 t, and 36 t and 19 t of top, respectively. The differences in monoculture crops occurred as a result of a plant loss during germination by 5.6%, and a smaller unit weight per root by 41.6%. The applied procedures of plant protection by herbicides and fungicides improved the root and top crop and favored the maintenance of plant density. A lowering of saccharose content in roots from 15.7% in the crop rotation to 15.0% in monoculture was recorded, and of sugar yield in the technological process from 13.0 to 12.3%, respectively. A high white sugar yield was obtained in crop rotation – 7.89 t per ha, while in monoculture it was only 4.06 t, i.e. 48.5% less.