Abstract
Vegetable crops are sometimes injured by gaseous nitrogen dioxide emerged from soil, when they are grown in the closed structure. In this study, the sensitivities of vegetable crops to NO2 as affected by environmental facfors and growth conditions were examined using kidney bean, cucumber, tomato and egg-plant. The crops were grown under different conditions of soil moisture and atmospheric humidity, and exposed to NO2 for several hours. They were injured more severely at high soil moisture and high humidity. Light exerted a great influence on the injury of crops by NO2. When the crops were exposed to NO2 in the dark, they were severely injured. However, they were little injured by the same concentration of NO2, when the light was present. Such an effect of light increased with its intensity. The crops were also resistant to NO2 when they were placed in the light before or after they were exposed to the gas in the dark. The plant age was another factor to affect the sensitivity. When juvenile kidney bean seedlings of different ages were exposed to the gas in the light, it became evident that younger primary leaves showed higher sensitivity. Degrees of injury of trifoliate leaves varied with leaf orders, middle leaves being the most sensitive to NO2. Vegetable crops supplied with a sufficient nitrogen fertilizer were more resistant to NO2 than those grown in the media including no or small amount of nitrogen. The crops supplied with nitrate nitrogen were more resistant than those with ammonium nitrogen. Plants grown in Fe-deficient condition were highly sensitive to NO2.
