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Soil Salinity and Ambient Ozone: Lack of Stress Interaction for Field-Grown Alfalfa

Statewide Air Pollution Research Center, University of California, Riverside, CA 92521;
U.S. Salinity Laboratory, ARS-USDA, Riverside, CA 92501.

^* Corresponding author.

ABSTRACT

The interaction of ambient photochemical oxidants (primarily ozone, O₃) and salinity on vegetation was evaluated in the field for ‘U.C. Salton’ and ‘Moapa’ alfalfa (Medicago sativa L.). Salinity treatments were imposed by irrigating with waters having average electrical conductivities of 0.9, 3.4, and 6.3 dS m^–1, which resulted in mean saturated-soil extract conductivities in the root zone of approximately 1.5, 5.8, and 8.1 dS m^–1, respectively. Plants were exposed in open-top chambers to filtered or unfiltered air at ambient O₃ concentrations during three regrowth periods, and filtered or unfiltered air plus added O₃ during a fourth. No overall interaction between O₃ and salinity occurred for alfalfa growth or yield. The only general effect of O₃ itself was to increase the percent empty nodes at three of the four harvests. Percent empty nodes due to ozone tended to decrease with increasing salinity, but the interaction was statistically significant only for the second harvest. Salinity by itself was more detrimental to plants than O₃, causing occasional decreases in dry weight and height. Large differences in growth and yield occurred between the two cultivars, but they were not associated with O₃ or salinity sensitivity. At the levels tested, salinity would affect plants more than O₃ in areas where both stresses occur.

Key Words: Air pollution • Crop loss • Medicago sativa L. • Yield

Joint Contribution from Statewide Air Pollution Research Center, University of California, and U.S. Salinity Laboratory, ARS-USDA.

Financial support for this research was provided in part by the California Air Resources Board under contract nos. A4-156-33 and A6-052-33. The statements and conclusions in this report are those of the contractor and not necessarily those of the California Air Resources Board. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such products by the Air Resources Board, University of California, or USDA.

Received for publication August 31, 1987.