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Title: Field assessment of the effects of ambient ozone on cotton (gossypium hirsutum) in the San Joaquin Valley

Principal Investigator / Author(s): Olszyk, David M

Contractor: Statewide Air Pollution Research Center, UC Riverside

Contract Number: A733-088

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Ecosystem Impacts, Field Studies


The primary objective of this study was to determine whether projected cotton yield losses due to ozone exposure, based on controlled experiments, actually occur in the field. This objective was addressed through three tasks. Task 1 was a determination of the percentage reduction in SJ2 cotton yield based on open-top field chamber research. The task was addressed with exposure to different ambient ozone concentrations at four sites in the San Joaquin Valley, using two filtered and two nonfiltered (ambient ozone) chambers per site. The chambers were placed over fields of cotton from approximately June through September, 1988.

Task 2 incorporated research with an antioxidant compound to determine if a chemical tool could be developed to determine ozone effects on crops without using chambers. The antioxidant sodium erythorbate (Ozoban) was used to represent a filtered air (reduced ozone) condition for plants for comparison to ambient ozone. Ethylene diurea (EDU) was also used on a limited basis. Two cotton cultivars, SJ2 and GC 510, were used with the antioxidants.

For task 3 the relative yields of 13 cotton cultivars were determined at each of eight sites in the San Joaquin Valley with different ambient ozone concentration. This aided in the evaluation of whether yield loss estimates based on research with SJ2 cotton are also valid for other cultivars.

Ozone monitoring indicated an ozone concetration gradient across the San Joaquin Valley. Ambient (plant height) ozone concentrations were highest at Dinuba (0.060 ppm), moderate at Shafter (0.056 ppm) and Hanford (0.049 ppm), and lowest at Five Points (0.044 ppm). These ozone concentrations were based on seven hour averages (0900-1600) for July through September, 1988.

Lint yields were significantly reduced by ambient ozone at Hanford and Dinuba. Yields were 16 and 34% lower in nonfiltered vs. charcoal filtered chambers at Hanford and Dinuba, respectively. The Hanford reduction was reasonable as it occured in a highly productive field. However, the cotton growing at Dinuba suffered from water deficiency and insect stress in different areas of the field, which may have exacerbated the ozone effect. The yield losses which occured in nonfiltered vs. charcoal-filtered chambers at the different sites were very close to those predicted based on the ozone exposure / yield loss models used in the Crop Loss Assessment Project. Thus, the losses reported for cotton from the crop loss project appeared to be reliable.

A large chamber effect on yield was also noted at Dinuba. Yields were also lower in nonfiltered vs. charcoal filtered chambers at Shafter (20% lower) and Five Points (13%), but the differences were not statistically significant. There was significantly greater leaf injury due to ambient ozone at Shafter and Hanford.

The antioxidant sodium erythorbate had no affect on cotton lint yields or leaf injury for either cultivar at any site. The concentration of the antioxidant was sufficient and applications frequent enought to affect the crop if the antioxidant was active.

The cultivar GC 510 had a significantly higher lint yield than SJ2 at Shafter where ozone concentrations were higher. The cultivar SJ2 had a higher yield at Five Points where ozone concentrations were lower. Thus, the relative yields of the two cultivarsat these sites would indicate that SJ2 is more susceptible to ozone than GC 510.

Lint yields for SJ2 tended to be lower than for most other cultivars at all sites in the southern San Joaquin Valley. The lower yields occured both at estimated high ozone sites such as Porterville and at low ozone sites such five points and Firebaugh, indicating that relative cultivar yields did not correlate well with response to ozone in different areas. Cultivar SJ2 performed best at the more northerly sites in Madera and Merced Counties. Estimated ambient ozone exposure (as surrogate for oxidants) did not significantly correlate with yield for any cultivar, based on analysis of yield and ozone concentrations at six of the cultivar trial sites. However, there was a trend toward decreased yields with higher ozone concentrations for cultivar CPCSD C-4226.

Overall, this project documented the effects of ambient ozone on cotton yields in the San Joaquin Valley, and indicated differences in cultivar response to ozone. Additional research is needed to more carefully determine the effects of ozone on plant development at the different sites, and especially to determine more precisely the concentration of ozone and its effects at Dinuba. Dinuba is of special interest because it is located in the high ozone area southeast of Fresno.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 322-3893

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