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Cotton Yield Responses to Ozone as Mediated by Soil Moisture and Evapotranspiration¹

ABSTRACT

A 2-yr field study was conducted to determine injury and yield responses of normally irrigated and water-stressed cotton (Gossypium hirsutum L.) to a gradient of ozone (O₃) concentrations. Cotton (cv. SJ-2), grown in open-top chambers in the Central Valley of California, was exposed to six O₃ treatments ranging from charcoal-filtered (CF) to ambient plus 0.10 µL L^–1 O₃ (1981) or twice ambient O₃ concentrations (1982) for the growing seasons of 1981 and 1982. Half the plots were irrigated optimally and the other half were provided with 25% (1981) or 20% (1982) less irrigation water (water-stressed treatment). During the typically hot, dry growing season of 1981, cotton yield in normally irrigated treatments was reduced 20% by ambient levels of O₃ in nonfiltered chambers (NF) relative to CF controls. Doubling ambient O₃ concentration reduced yield 45%. Water-stressed plants showed almost no response to O₃. In 1982, the weather was cooler and cloudier than normal and potential evapotranspiration during the growing season averaged 20% less and ambient O₃ concentrations averaged 39% lower than in 1981. Under these conditions, cotton yields at both levels of soil moisture treatments responded similarly to O₃. Yields in NF chambers were reduced 15% relative to CF chambers. Doubling ambient O₃ concentrations reduced yields 65%. The greater relative response of cotton to O₃ in 1982 may have resulted from the cooler, more humid growing conditions, which increased the susceptibility of cotton to O₃.

Key Words: air pollution • dose-response functions • water stress • Gossypium hirsutum L • herbicides

¹ Contribution from the Statewide Air Pollution Research Center, Univ. of California, Riverside, CA 92521. Although financial support for this research was provided in part by Cooperative Agreement CR807399 with the USEPA, it has not had USEPA's required peer and policy review and thus does not necessarily reflect the views of the agency. Mention of a product does not constitute a guarantee or warranty by the Univ. of California or USEPA and does not imply endorsement of it to the exclusion of other products.

² Assistant research botanist, professor of plant science, and postgraduate research associate, respectively.

Received for publication March 5, 1984.