Ozone Effects on Agricultural Crops: Statistical Methodologies and Estimated Dose-Response Relationships

The National Crop Loss Assessment Network (NCLAN) began in 1980 to coordinate research on the impact of ozone (O₃) on agricultural crops. During a 7-yr period, the program investigated 14 crops at sites across the country in a total of 41 studies. A major objective was to develop dose-response relationships between yield of major agricultural crop species and ozone pollution in order to estimate the economic impact of ozone pollution. This paper outlines the statistical methodologies used in combining the dose-response information for each species over all NCLAN studies, and summarizes the ozone dose-response relationships obtained. Differences in experimental designs, treatment combinations, and levels of ozone across studies invalidated the conventional analysis of variance approach to combining information across studies. Regression analyses, with weighted least squares and transformations as needed, were used. Dose-response relationships between yield and ozone were quantified with the nonlinear Weibull response equation and with confidence interval estimates of percentage yield losses. Significant yield losses from ozone were found for 13 of 14 crops studied. The nature of the yield response to ozone differed among crops with soybean [Glycine max (L.) Merr.] being the most sensitive and showing a nearly linear response. Losses from ozone at 0.06 μL L∑¹ compared with 0.025 μL L⁻¹ were estimated as high as 20%. The impact of ozone was shown to be affected by level of moisture stress but not by SO₂. Present address for V. M. Lesser, Department of Biostatistics, University of North Carolina at Chapel Hill. Chapel Hill NC 27699-7400. Journal Series Paper no. 12039 of the North Carolina Agric. Res. Ser., Raleigh, NC 27695-8203. Research partly supported by Interagency Agreement no. DW 12931347, and Specific Cooperative Agreement no. 58-43YK-6-0041 between the USDA and the North Carolina Agric. Res. Serv.