The Effects of Acid Rain, Alone and in Combination with Gaseous Pollutants, on Growth and Yield of Crop Plants

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Greenhouse, growth chamber, and field experiments were conducted to determine the response of crop plants to levels of acidity in simulated rain. The major objectives of this research effort were: (1) to determine the levels of acidity in rain that alter crop productivity, (2) to evaluate varietal differences in crop response, and (3) to determine the response of crop plants to the combined stress of acid rain and gaseous pollutants [primarily ozone (O3)]. In the greenhouse, plants were exposed to either four or six levels of acidity twice per week with a rain simulator. In the growth chamber experiments, gaseous pollutant fumigations were conducted either once or three times weekly with a continuously stirred tank reactor exposure system. In the field, open-top field chambers were used in conjunction with an automatic rain exclusion-simulant distribution system to expose crops to controlled levels of gaseous pollutants and rain acidity. In an experiment with tomato cultivars, pH 2.3 rain applied to both foliage and soil reduced growth, while the same solution applied to the soil without foliar contact increased growth. The growth response of radish and alfalfa plants to the combined stress of acid rain and ozone was additive. The visible injury response of younger radish leaves to combinations that included pH 3.3 rain and 0.2 and 0.4 ppm of O3 was less than additive. In field studies, Davis soybeans snowed no significant growth or yield responses to ambient O3 levels, or simulated rain at pH 5.2, 4.2 or 3.2. There was a small (−3%) rain treatment (pH) effect on weight per seed in the pH 4.2 simulated rain and the ambient rain treatments (also ~pH 4.2).