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Effects of Growth Medium and Fertilizer Rate on the Yield Response of Soybeans Exposed to Chronic Doses of Ozone. A. S. Heagle, Plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, North Carolina State University, Raleigh 27650; M. B. Letchworth(2), and Cindy A. Mitchell(3). (2)(3)Research assistant and biologist, Department of Plant Pathology, North Carolina State University, Raleigh 27650. Phytopathology 73:134-139. Accepted for publication 9 June 1982. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/Phyto-73-134.

The objectives were to determine whether wide variation in fertilizer rates or type of growth medium would affect the response of soybeans, Glycine max 'Davis' exposed to chronic doses of ozone (O₃) in open-top field chambers. Responses to O₃ were compared for plants grown in the ground or in pots containing an artificial growth medium. In 1977, the yield of plants grown in pots containing soil, sand, and a mixture of perlite, peat moss, and vermiculite was greater than that of plants grown in the ground; in 1978, the reverse was true. However, the percentage yield loss caused by O₃ was not affected by the growth medium either year. Separate tests were made for potted plants that received different levels of fertilizer. At moderate fertilizer rates, the yield response to different doses of O₃ was not significantly affected by fertilizer rate for either year. In 1978, plants with no fertilizer added were severely stunted and even relatively high doses of O₃ did not further decrease yield. The results suggest that plant response to O₃ will be fairly uniform over a range of substrate types and fertilizer rates when edaphic conditions are adequate to insure normal plant growth.