Twelve species of fruit vegetables were grown in solution culture in order to compare the growth and nitrogen assimilation between them, using NO
3, NO
3+NH
4, NH
4, NO
3+NO
2, and NO
2 as nitrogen sources. The experiment consisted of 4 kinds of treatment conditions where 2 levels of nitrogen concn (2me/
l designated as low-N and 12me/
l as high-N) and 2 levels of solution pH (5 and 7) were combined. Plants were grown under different treatments for about 3 weeks.
1. When plants were supplied with NO
3, the growth of vegetables, in general, was better in high-N than in low-N regime, though kidney beans grew better in low-N than in high-N regime. In the NO
3 treatment, solution pH exerted almost no effect on plant growth except for sweet corn which showed somewhat inhibited growth at pH 7.
2. In general, fruit vegetables fertilized with NO
3+NH
4 grew well under any cultural conditions. Plant growth of the NO
3+NH
4 treatment was better than or almost equal to that of the NO
3 treatment.
3. Solution pH and nitrogen concn showed pronounced effects on growth of the plants cultured with NH
4 as a nitrogen source, i.e., NH
4 tended to reduce the plant growth markedly under high-N at pH 5, but not under low-N at pH 7. In comparison with NO
3, the growth of kidney beans, tender soybeans, peas, tomatoes, and sweet peppers was inhibited with NH
4, while the growth of sweet corn and strawberries was not. When plants were cultured with NH
4, a relatively close relationship was observed between growth response and leaf NH
4-N concn, i.e., the better the plant growth, the lower the NH4-N concn in leaves. In several fruit vegetables, growth responses of plants to NH
4 seemed to have a relation with NH
4-N/amide-N ratio or insoluble-N/total-N ratio of the leaves.
4. In general, NH
4 nutrition reduced leaf concn of K, Ca, and Mg as compared to NO
3. Such reduction in concn of leaf basic elements was remarkable in sweet peppers, tomatoes, and watermelons, but only slight in sweet corn and strawberries.
5. Growth responses of plants to NO
3+NO
2 and NO
2 were severely affected by pH and nitrogen concn of nutrient solution, i.e., plant growth was inhibited more markedly at low pH and high N concn. However, the growth of some vegetables cultured under low-N of NO
3+NO
2 and under low-N of NO
2 at pH 7 was comparable to that of NO
3 plant. When cultured with solutions containing NO
2, the growth of melones, eggplants, cucumbers, and sweet corn was relatively good, though the growth of kidney beans was markedly restricted. On the other hand, the growth of peas, tender soybeans, and tomatoes which were supplied with NO
2 was good only under low-N at pH 7. Okra was the most sensitive to NO
2 toxicity at pH 5, whereas at pH 7 this plant seemed to belong to a group of most NO
2-tolerant vegetables. When plants were supplied with NO
2, no significant interrelations were observed between growth responses and leaf concn of nitrogenous constituents and/or composition of inorganic elements in leaves.
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