1979 Volume 47 Issue 4 Pages 454-462
Twelve species of fruit vegetables were grown in solution culture in order to compare the growth and nitrogen assimilation between them, using NO3, NO3+NH4, NH4, NO3+NO2, and NO2 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 NO3, 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 NO3 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 NO3+NH4 grew well under any cultural conditions. Plant growth of the NO3+NH4 treatment was better than or almost equal to that of the NO3 treatment.
3. Solution pH and nitrogen concn showed pronounced effects on growth of the plants cultured with NH4 as a nitrogen source, i.e., NH4 tended to reduce the plant growth markedly under high-N at pH 5, but not under low-N at pH 7. In comparison with NO3, the growth of kidney beans, tender soybeans, peas, tomatoes, and sweet peppers was inhibited with NH4, while the growth of sweet corn and strawberries was not. When plants were cultured with NH4, a relatively close relationship was observed between growth response and leaf NH4-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 NH4 seemed to have a relation with NH4-N/amide-N ratio or insoluble-N/total-N ratio of the leaves.
4. In general, NH4 nutrition reduced leaf concn of K, Ca, and Mg as compared to NO3. 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 NO3+NO2 and NO2 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 NO3+NO2 and under low-N of NO2 at pH 7 was comparable to that of NO3 plant. When cultured with solutions containing NO2, 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 NO2 was good only under low-N at pH 7. Okra was the most sensitive to NO2 toxicity at pH 5, whereas at pH 7 this plant seemed to belong to a group of most NO2-tolerant vegetables. When plants were supplied with NO2, no significant interrelations were observed between growth responses and leaf concn of nitrogenous constituents and/or composition of inorganic elements in leaves.
