In order to make comparison among vegetables in growth response to nitrogen source and accumulation of NH
4-N and NO
3-N in leaves, potato, carrot, radish (
Raphanus sativus L. radicula group), turnip, and japanese radish (
Raphanus sativus L. daikon group) were cultured in nutrient solution containing NO
3, NO
3+NH
4(1:1), NH
4, NO
3+NO
2 (1:1), and NO
2 as nitrogen sources. The experiment consisted of 4 kinds of treatment conditions where 2 levels of nitrogen concentration (2meq/l designated as low-N and 12meq/l as high-N) and 2 levels of solution pH (5 and 7) were combined. Plants were grown under each treatment for about 3 weeks.
1. All root vegetables fertilized with NO
3 and NO
3+NH
4 showed normal appearance with healthy leaves and grew well under all treatment conditions. The growth of root (edible portion) was often considerably better under NO
3+NH
4 than NO
3 nutrition.
2. When plants were supplied with NH
4, the top growth of potato and carrot was relatively good and the NH
4-N concentration in their leaves was low. On the contrary, the top growth of turnip and japanese radish was inhibited extremely in NH
4 nutrition and the NH
4-N concentration in their leaves was high. The highest NH
4-N concentration, however, was detected in leaves of radish which showed intermediate growth between aforesaid 2 groups. The concentration of NH
4-N in leaves of plants which showed markedly restricted growth in NH
4 was a few times as much as the concentration of amide-N.
3. Nitrite toxicities were more intensive under lower solution pH and higher N concentration. The difference of growth response of root vegetables to nitrogen sources was not clear under NO
3+NO
2 or NO
2 nutrition.
4. The concentration of NO
3-N in leaves was scarcely affected by solution pH but was affected markedly by N forms and levels in nutrient solution Under high-N treatment, the concentration of NO
3-N in leaves of turnip and japanese radish was more than 2% on a dry weight basis. The concentration of NO
3-N in leaves of NO
3+NH
4 plants was, in general, lower than NO
3 plants under low-N treatment, while no difference was detected between them under high-N treatment. Apparently low NO
3-N concentration was detected in roots(edible portion)as compared in leaves.
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