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Effects of Water and Salt Stress on Growth and Acetylene Reduction in Alfalfa¹

ABSTRACT

The interactive effects of three irrigation water salinities (1.0, 3.0, and 9.0 dS/m) and three quantities of water applied per irrigation (2.3, 4.7, and 7.0 cm) on plant growth and N fixation by alfalfa (Medicago sativa L. cv. Resistador) were assessed in the greenhouse. Salt and water treatments were started after nodulation had been established in young plants and samples were harvested at 10, 30, and 50 d thereafter. Alfalfa top growth was limited by both salt and water stresses. Irrigation water salinity had a greater effect on top growth than root growth while root distribution was unaffected by either the quantity of water applied or by water salinity. The effects of salinity on plant growth were masked by water stress. Specific nodule activity (µmol C₂H₄ s^–1 kg^–1) was enhanced by increasing quantity of water applied at each irrigation and was adversely affected by increased irrigation water salinity. In contrast, both nodulation and total nodule mass were insensitive to salt stress and sensitive only to severe water stress. Alfalfa plants continued to reduce acetylene at the third sampling even under severe water and salt stress. These data indicate that the Resistador cultivar of alfalfa apparently continues to fix N₂ during periods of substantial environmental stress.

¹ Joint contribution from the Dep. of Soil Science and Biometeorology, Utah State Univ., Logan, UT and the Dep. of Agronomy, Cornell University, Ithaca, NY. Utah Agric. Exp. Stn. Jour. Paper no. 2797.

² Graduate Research Assistant, Associate Professor of Soil Science, Professor of Plant Science, and Graduate Research Assistant, respectively. Current address of second and fourth authors is: Dep. of Agronomy, Cornell University.

Received for publication April 2, 1984. Accepted for publication July 9, 1984.