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Injury and Yield Responses of Differentially Irrigated Cotton to Ozone

Statewide Air Pollution Res. Ctr., Univ. of California, Riverside, CA 92521

^* Corresponding author.

The hypothesis that plants subjected to drought stress should be less susceptible to air pollution than well-watered plants has not been adequately tested in the field. This study was conducted to determine the influence of drought stress on foliar injury and yield responses of field-grown cotton (Gossypium hirsutum L. cv. Acala SJ-2) to O₃. Cotton grown on Hanford coarse sandy loam (coarse-loamy, mixed, non-acidic, thermic Typic Xerorthents) at three levels of soil water in open-top chambers was exposed to seasonal 12-h (0900-2100 h) O₃ concentrations of 0.015, 0.074, 0.094 and 0.111 µL L^–1 in Riverside, CA. At ambient O₃ concentrations (0.074 µL L^–1) severely drought-stressed (SS) cotton averaged 25% foliar injury, while moderately stressed (SO) plants averaged 56%, and optimally watered (OW) plants averaged 68% foliar injury. Lint and seed yields were significantly reduced by O₃ in OW and SO plots, while SS cotton showed no yield reductions, except at 0.111 µL L^–1. Yield reductions were primarily attributable to fewer numbers of bolls. Regression equations for lint yield in relation to seasonal 12-h O₃ means and total seasonal irrigation predicted yield losses at ambient O₃ concentrations relative to a background O₃ level of 0.025 µL L^–1 of 26.2% for OW, 19.8% for SO, and 4.7% for SS cotton. The relative similarity in responses of OW and SO cotton was attributed to adaptation to drought stress by SO plants, which maintained the sensitivity of moderately stressed cotton to O₃. These results suggest that low or moderate drought stress would have relatively little effect on the response of irrigated cotton to O₃.

Received for publication September 3, 1987.