THE EFFECTS OF HIGHER CARBON-DIOXIDE CONCENTRATION IN THE KOHLRABI GROWING ON NITRATE CONTENTS IN THE BULBS

The varietal differences have been studied for nitrate contents in the controlled hydroponic system with artificial lighting in a glasshouse and in the phytotron in the kohlrabi bulbs of grown units under the conditions of higher controlled atmosphere with normal concentrations of carbon dioxide (340-mu-l per l) or at higher concentration (1,000-mu-l per l). White earlier varieties exhibited lower nitrate contents than in the later ripening blue varieties. White varieties differed from blue varieties by lower specific weight. The plants growing under the conditions of lower carbon dioxide concentrations had always higher weight in comparison with the control owing to the higher photosynthetic production. There were found no differences between variants with increased and normal carbon dioxide concentration in nitrate contents in the phase of plants with small undeveloped bulbs. High negative correlation was found between bulb weight and nitrate contents in the plants with more developed bulbs and bulbs filling out. The effects of carbon dioxide on the reduction of nitrate contents were manifested by the shift of the bulbs to the higher degree of their filling out. The atmosphere enriched with carbon dioxide thus helped to decrease nitrate contents in bulbs in comparison with the control by 37 % in the phytotron and by 25 % in the glasshouse. The most significant decrease in nitrate contents, that is by 57 %, however, was confirmed to be successful through elimination of the nutrient solution with nitrate contents and by its replacement by fresh water a week before harvest.