Date of Award:

5-1-1979

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

John J. Skujins

Committee

John J. Skujins

Committee

Frederick J. Post

Committee

Raymond I. Lynn

Committee

Jon Y. Takemoto

Committee

R. L. Smith

Abstract

Two legume species were evaluated for their potential use as cover crops in rehabilitating arid and semi-arid saline soils. Vicia villosa and Melilotus officinalis were tested for their ability to nodulate and maintain an effective symbiosis in saline soils when soil moisture was adequate and under drought conditions. Calcium chloride and sodium chloride were added to a silt loam soil at a rate which provided soil saturation extracts with electrical conductivities (ECe) of 4, 8 and 12. For drought studies, soil water potential was measured in pots, using thermocouple psychrometers. Nitrogen fixing activity was assessed by the acetylene reduction assay. With V. villosa decreases in acetylene reduction and yield correlated well with increasing soil salinity. Decreased plant nitrogen contents at high salinity levels reflected lowered rates of acetylene reduction. Salinized V. villosa plants showed greater relative recovery rates of nodule sepcific activity than plants in non-saline soils when subjected to short term drought stress followed by a recovery period. M. officinalis showed yield decreases of 30 percent at ECe12 and acetylene reduction rates remained at relatively high levels. Both nodulation and nodule specific activity decreased rapidly with small changes in water potential. With M. officinalis there was little or no recovery of nodule activity following drought stress.

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