Project at a Glance

Title: Determination of the effects of photochemical oxidants and/or SO2 on yield of navel oranges

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

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

Contract Number: a2-130-33

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Agriculture, Ecosystem Impacts


The ozone and sulfur dioxide sensitivity of California citrus trees is being tested using Valencia orange trees (Citrus sinensis). The trees were planted in soil at a newly developed research site on the Agricultural Experiment Station of the University of California, Riverside, on July 25, 1983. The site was extensively prepared before planting by testing the soil for nutrient concentrations, fumigating the soil for soil-borne pathogens, installing an underground irrigation system, and leveling the area. A new type of open-top field chamber was designed, constructed, and tested for use with the orange trees. The chamber system consisted of a 4.27 m diameter, 2.03 m high vinyl bubble over the tree canopy; a 0.91 m high fiberglass base; a fiberglass door; a blower box containing a 3/4 hp motor, axial blade fan, fiberglass particulate filters, and metal-activated charcoal filters; a sheet metal mixing duct between blower and chamber base; and a sheet metal diffusing panel inside the chamber in front of the air entrance port. The chambers were placed over the trees in late March, 1984 and the pollutant exposures were initiated on May 22, 1984. Twenty-eight chambers were constructed and placed over trees to provide four pollutant treatments with seven trees per treatment e.g. filtered air, ambient air, one-half filtered air, and filtered air plus 0.10 ppm SO2. All treatments were continuous from the time of experiment initiation. There were seven chamberless outside control trees. None of the tree growth or physiological status parameters, e.g. leaf drop, stomatal conductance, net photosynthesis and water potential; indicated any effects attributable to the different pollutant treatments. The chamber itself significantly increased leaf drop compared to outside trees. Small increases in leaf and air temperatures, and a small decrease in light intensity were found in the chambers compared to outside trees. No fruit were set on the chamber trees during the 1984-1985 growing period. Both chamber and outside trees had a large flower production during late winter 1985 which will provide the first definite indication of effects of the air pollutants on yield at the June 1986 harvest.

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

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