Research Program Area: Ecosystem & Multimedia Effects
A study designed to assess the affects of existing and potential levels of oxidant air pollution on cotton growing in the Central San Joaquin Valley was conducted near Parlier, California in 1978. Acala SJ-2' and Acala SJ-5 varieties of cotton were grown in open top plastic covered chambers supplied with varying concentrations of ozone achieved by either filtering existing ozone from the ambient air or adding electrically generated ozone to ambient air. Four air treatments were used in the chambers: ambient or non-filtered air, filtered air passed through activated carbon filters, a mixture of two-thirds ambient and one-third filtered air, and ozone-enriched ambient air with the ozone level raised to approximately twice the ambient level whenever the ambient level exceeded .05 ppm.
Approximately ten days after the enhanced ozone treatment was begun, ozone toxicity symptoms were observed on both SJ-2 and SJ-5 cotton foliage. Similar but less severe symptoms were observed on SJ-2 plants in the ambient treatment three weeks later. Similar symptoms did not appear on SJ-5 until treatment three weeks later. Similar symptoms did not appear on SJ-5 until the last week in October, nearly two months later, than on SJ-2.
The primary response by cotton to increased ozone levels was a reduction in the number of bolls set per plant. Boll set by SJ-2 plants was 12% less in ambient than in filtered air. Where ambient ozone levels were doubled, boll set reduction approached 17% for both SJ-2 and SJ~5. There was no significant difference in SJ-5 boll set between the filtered and ambient treatments.
Production of raw cotton fiber and seed by SJ-2 varied inversely with ozone dose, ranging from a 34% reduction resulting from doubling ambient ozone levels, to 8% from exposure to two-thirds ambient ozone levels. Ambient ozone reduced SJ-2 yields 14%. Raw cotton production by SJ-S at ambient and two-thirds ambient ozone levels were essentially the same as in filtered air; however, doubling the ambient ozone concentration reduced SJ-S raw cotton production 25%. Lint quality was also reduced by exposure to ozone.
These experiments indicate that Acala SJ-2, which accounts for approximately 70% of the San Joaquin Valley's cotton crop, is now being seriously damaged by ozone levels prevailing on the east side of the valley, and should present ozone levels increase significantly, SJ-5, apparently not damaged by present levels, would also be damaged.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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