Cotton Yield Losses and Ambient Ozone Concentrations in California's San Joaquin Valley

Olszyk, D.; Bytnerowicz, A.; Kats, G.; Reagan, C.; Hake, S.; Kerby, T.; Millhouse, D.; Roberts, B.; Super C.,; Lee, H.

Cotton Yield Losses and Ambient Ozone Concentrations in California's San Joaquin Valley

1993

Based on controlled experiments and simulation modeling, ozone (O₃) has been estimated to cause significant yield losses to cotton. The study reported here was conducted to verify losses for ‘Acala’ cotton (Gossypium hirsutum L. ‘SJ2’) along a gradient of ambient O₃ concentrations across the San Joaquin Valley in California. Cotton was grown in nonfiltered (NF) and charcoal-filtered (CF) open-top chambers, and ambient air (AA) at four sites during the 1988 and 1989 summer growing seasons. Cotton yields (weights of mature bolls m⁻²) were reduced in NF compared with CF air in general proportion to O₃ concentrations across all sites and years. Greatest cotton yield losses were as Shafter in the southern part of the San Joaquin Valley (20% in 1989), and lowest losses were at Five Points in the western part of the valley (none in 1989). Ozone injury symptoms on cotton were most noticeable in areas with greatest yield losses. Linear O₃ exposure vs. predicted relative yield loss models using four common exposure indices were constructed for each site and year based on the NF, CF, and AA data. All models except the second highest daily maximum concentration (2ndHDM, the current ambient air quality standard for O₃) predicted yield losses comparable to those predicted with previously published models for cotton in the San Joaquin Valley. Ozone exposure indices giving more weight to higher O₃ concentrations or the 7-h daytime mean better predicted cotton yield responses over the growing season than 2ndHDM.

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