Modeling the response of greenhouse-grown radish plants to acidic rain

The emphasis being placed on the need for assessments to determine the impacts of acidic rain has resulted in the initiation of many dose-response studies. Experimental design parameters and model evaluation play important roles in the overall conclusions of such studies. To illustrate the importance of some of these factors, three dose-response studies on radish (Raphanus sativas L.) plants exposed to simulated rain were performed in a greenhouse. Significant negative effects on marketable yield occurred from simulated rain having pH levels below 3.8 in one experiment and below 3.4 in another. The apparent threshold level may have been dependent on environmental conditions which affected overall growth rates. In modeling the experimental results, treatments having very high levels of acidity had an overwhelming influence on the dose-response function used to describe the results. Plants treated with the highest acidity levels had reduced leaf area which resulted in lower photosynthesis per plant and may have been responsible for the reduced yields of plants. In addition to acidity, the sulfate to nitrate ratio in simulated rain also influenced radish response. Nitric acid appeared to have a greater effect than sulfuric acid in reducing yield at pH 3.0.