Project at a Glance

Title: Effects of ozone or SO2 on growth and yield of rice

Principal Investigator / Author(s): Thompson, C. R.

Contractor: Statewide Air Pollution Research Center, University of California, Riverside

Contract Number: a1-111-32

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Agriculture, Ecosystem Impacts, Impacts


Three cultivars of rice produced commercially in California, M7, M9 and S201, were grown in pots, six plants per pot and were flooded continuously with tap water and supplied with all known mineral elements. The plants were provided with activated carbon filtered air to which ozone or S02 was added as a fumigant. Twenty greenhouses were divided randomly into 10 groups of two each. Twelve pots of each cultivar (36 pots/green- house) were fumigated as follows: ozone 0.05, 0.10, 0.15 and 0.20 ppm for 25 hrs/wk plus one treatment of 0.25 ppm for 5 hrs/wk; SO2 0.05, 0.10, 0.15 and 020 ppm for 104 hours/week. Two greenhouses received carbon filtered air (controls).

Three successive harvests were made of one plant, one plant and four plants per pot. Parameters determined were height of plant, total dry weight, number of tillers, number of panicles, total seed weight, weight of 100 seeds, percent of sterile seeds, straw weight, number of spikelets per panicle and total biomass.

Results of the first harvest showed that ozone reduced dry weight of all cultivars but S02 increased this parameter with M9. The second harvest showed no effect of S02 but 0.20 ppm ozone reduced numbers of tillers in M9 but increased the numbers in S201. The final harvest showed that ozone reduced seed weight, height of plant and spikelets per panicle but increased number of panicles in all cultivars and reduced straw weight in M9 and S201. It increased percent of sterile seed in these two cultivars. Seed weights were reduced 13, 30 and 24% in M7, M9 and S201, respectively, by 0.20 ppm ozone. Sulfur dioxide at this level reduced seed weight 28 and 17% with 1,49 and S201, respectively, and the height was reduced in S201. S02 increased the number of panicles significantly in M9. These results show that ozone is much more toxic per unit of pollutant than S02. Roughly equal effects were produced by one-fourth the total exposure to ozone. Cultivar M7 is less susceptible to either ozone or SO2 than M9 or S2O1. A pronounced positional effect within the chamber occurred. Plants in the center yielded better than those on the periphery. Reduced pollination is suspected because of the constant flow of incoming air. Further work should explore the interactions of these two pollutants on rice so that environmental planners can predict the effects of increased SO2 levels with existing amounts of ozone on rice production in California.

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

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