Abstract
Twelve species of vegetable crops were grown in solution culture with varying nitrite and pH levels. Nitrate and nitrite of sodium were used as the nitrogen sources. Nitrite was supplied at rates of 0, 4, 8, or 12me/l, with the total nitrogen concentration being held constant at 12me/l. At each nitrite level the pH of the solution was adjusted to three levels, 5, 6, or 7. The plants were grown under differential treatment for four weeks.
1. The nitrite toxicity was increased by low pH level. At pH 5 plants supplied with nitrite showed root browning, leaf wilting, dark green leaves, and stunted growth with increasing severity as the nitrite concentration was increased. In some species nitrite at pH 5 also produced leaf-burn, chlorosis, or flecks on leaves. At pH 6 or 7 nitrite was less injurious than at pH 5, but iron deficiency chlorosis was caused by nitrite in some species including tomato and pepper. The more the pH decreased, the more the nitrite treatment killed plants.
2. The growth inhibition by nitrite was more marked at lower pH levels. The relative tolerance of vegetable crops to nitrite was evaluated on the basis of relative dry weight yield as affected by nitrite at the three pH levels and was found to be in the following order : cabbage>cucumber>Japanese hornwort>egg plant>celery>welsh onion>carrot >lettuce>tomato>spinach>pepper>bean. The nitrite tolerance varied greatly with the species.
3. The effect of nitrite treatment on the concentration of total nitrogen in leaves varied with the crop species. Nitrate nitrogen in leaves apparently decreased with the decreasing supply of nitrate in the nutrient solution. The nitrite treatment mostly reduced the concentration of phosphorus, potassium, calcium, and magnesium in leaves. The effect of nitrite on the concentration of heavy metal elements, Fe, Mn, and Zn in leaves was variable with the crop species.
