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Salinity-Ozone Interactive Effects on Alfalfa Yield and Water Relations¹

ABSTRACT

The effect of ozone on forage yield of alfalfa (Medicago sativa L. cv. Moapa) was determined at four controlled salinity levels. Plants were grown in gravel cultures in four environment-controlled, sunlit chambers. Four salinity treatments (NaCl and CaCl₂) having osmotic potentials of –40, –200, –400, and –600 kilopascals (kPa) were replicated four times in each chamber. Alfalfa grown in ozone-free chambers was compared with plants exposed to ozone 2 hours every day between cuttings.

For nonsaline treatments, ozone at 10, 15, and 20 parts per hundred million (pphm) reduced forage yield by 16, 26, and 39%, respectively. As salinity increased, ozone had less effect on yield. Alfalfa exposed to 20 pphm of ozone for 2 hours daily yielded 25% more at –200 kPa osmotic potential than at the nonsaline level, –40 kPa. The residual effect of ozone treatments reduced yield in the next cutting. Salinity at all levels or ozone at 20 pphm increased water-use efficiency of alfalfa; low concentrations of ozone had no effect on water-use efficiency. Both ozone and salinity were required to increase leaf diffusion resistance; either factor alone had no effect.

Key Words: air pollution • plant growth • leaf diffusion resistance • transpiration • osmotic potential • salt tolerance • water-use efficiency

¹ Contribution from the U. S. Salinity Lab., Agricultural Research Service, USDA, P. O. Box 672, Riverside, CA 92502.

² Agricultural Engineer, Plant Physiologist, and Supervisory Soil Scientist, respectively.

Received for publication September 16, 1974.

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