Project at a Glance

Title: Effects of ozone and SO2 on alfalfa yields and hay quality.

Principal Investigator / Author(s): Brewer, Robert

Contract Number: A1-038-33

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Agriculture, Ecosystem Impacts


Alfalfa (Medicago sativa L.) is an extremely important crop in California, ranking only below number 1 cotton and number 2 grapes indollar value. Although alfalfa has long been recognized as especially sensitive to damage by air pollution, it is only in recent years that attempts have been made to quantify the relationship between exposure and economic damage. Most previous studies involved container-grown plantsand involved only a few cuttings. An air pollution effects experiment more nearly approximating "field conditions" was initiated at the University of California San Joaquin Valley Research and Extension Center near Reedley in the spring of 1979. Two varieties of alfalfa, Moapa and WL-512 were grown in prepared soil beds surrounded by 12-foot square, open top, blower-ventilated, plastic covered chambers. Seventeen hay cuttings were harvested over a period of three seasons from alfalfa plots exposed to varying amounts of ozone (three levels) with and without S02. Both the quantity and quality of each cutting was measured and correlated with pollutant doses calculated by totaling the mean hourly averages greater than 10, 5 or 15 PPHN.


The two alfalfa varieties responded quite differently to ozone. Ambient ozone concentrations (season dose of approximately 75-100 PPHM-hrs over threshold of 10) reduced Moapa yields approximately 8 to 13% but had no measureable effect on variety WL-512. Exposure to a SO2 concentration of 10 PPHM for six hours four times per week reduced yields by both varieties approximately 9%. Moapa yields were reduced approximately17% by a combination of ambient ozone levels and the SO2 treatment. Increasing the ambient ozone concentration by 50% decreased yields by Moapa an additional 19% for a total of 27% compared with the pollution-free, filtered air treatment. WL-512 yields were depressed approximately 10% by the high ozone treatment, indicating that even this "ozone tolerant" variety would suffer significant economic damage if San Joaquin Valley air quality were to deteriorate to the levels used in this experiment. There was no indication that ozone and SO2 in the concentrations used are synergistic, but their effects are additive. Stand counts made in the spring and fall of 1980 and 1981 indicated increased Moapa mortality with increasing ozone pollution dose, and increased mortality of both varieties with exposure to SO2.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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