Potassium and nitrogen distribution pattern and growth of flue-cured tobacco seedlings influenced by nitrogen form and calcium carbonate in hydroponic culture

The influences of nitrogen form (NH4(+), NO3(-), and NH4NO3) with or without CaCO3 on the growth and potassium (K) and nitrogen (N) uptake and partitioning of flue-cured tobacco plants (Nicotiana tabacum L. cv. 'K326') were examined under the controlled conditions of nutrient-solution culture. Tobacco seedlings with four true leaves were grown in mixed substrate before being transplanted and grown in a pre-culture solution until the six-true-leaf stage. The following treatments were applied: NH4(+)-, NO3(-)-, and NH4NO3 alone, and each of these in combination with CaCO3. Seventeen days later, the plants were harvested. The results showed that NH4(+) as the only N source resulted in lower dry weight of both leaves and roots compared with other N forms, including NO3(-) and NH4NO3, without obvious ammonia toxicity in leaves. The CaCO3 addition was beneficial in ameliorating the growth suppression found in NH4(+)-only plants, but the same effects of addition were not found in NO3(-)-only plants. Sole NH4(+) nutrition led to the lowest K concentration and content in leaves and roots, while sole NO3(-)-only plants had the highest. Added CaCO3 also significantly improved the K concentration and content in NH4(+)-only plants. However, NH4(+) nutrition resulted in more K translocated to leaves than did NO3(-) supply. Nitrogen concentration and content were only weakly affected by N form. Although NH4(+)-only plants had the lowest N concentration and content in plants, there was no difference in N concentration in top leaves and roots between NH4(+) and NO3(-)-plants. Added CaCO3 also improved the N concentration in NH4(+)-only plants. In contrast to its effect on K partitioning, the NH4(+)-only treatment the lowest N concentration in leaves, while no differences in N partitioning were observed under other treatments. These results suggest that long-term use of 100% NH4(+) in the nutrient solution reduces dry-matter accumulation and K uptake in tobacco plants and increases K accumulation in leaves. Added CaCO3 could reduced the suppression induced by 100% NH4(+) to a certain extent.