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

Abstract

AbstractA 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.