Abstract
To determine the optimum range of N in the medium for normal growth, in particular to establish the lower critical level, the chrysanthemum plants were grown on soil media and nutrient solutions with various concentrations of N.
In an experiment with soil media (Expt. I), the plants were supplied with 12.5, 25, 50, 100, 200 and 400g of NO3-N per m3 soil on July 14, 1985, 16 days after pinching, and were grown for 15 days, receiving a small amount of liquid NO3-N every day. All plants initially supplied with 12.5-50g/m3 N grew well, but higher levels of N inhibited growth.
In Experiment II, the plants were grown on nutrient solution at 50, 100, 200 and 300ppm of NO3-N for 16 days from the 15th day after pinching (Aug. 12, 1985). Another group of plants did not receive N for the initial two days, and then on every other day they received the same amount of NO3-N as absorbed by the plants receiving 100ppm during the previous two days. In that case the N concentration was maintained at 0-21.1ppm. The N level of the nutrient solution had no effect on the rate of plant growth. Even at a concentration of 0-21.1ppm the plants grew vigorously, and two days later their fresh weight reached the same level as that of plants grown at 100ppm.
When the plants grew normally, the N level of the medium did not affect the concentration of N in the plant tissue, but at higher N levels, which inhibited growth, the concentration of N in the tissue increased.
From these results, it can be concluded that the optimum range of N in the medium for normal growth of chrysanthemum plants is relatively wide, and that the lower critical level is very low. Normal growth can be achieved if the plants steadily receive as much N as they absorb.
