Date of Award:

1-1-1982

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Advisor/Chair:

R. J. Wagenet

Abstract

A greehhouse study was conducted to assess the interactive effects of three irrigation water salinity levels (1 . 0, 3. 0, and 9 . 0 mmho/cm) and three quantities of water app lied per irrigation (120 , 240, 360 ml) on plant growth and nitrogen fixation by alfalfa (Medicago sativa L. cv. Resistador). Harvest dates corresponded t o 10, 30, and 50 days after the initiation of salt and water treatments which were started after nodulation had been established in young plants.

Alfalfa top growth was limited by both salt and water s tresses. Irrigation water s alinity had a grea t er effec t on top growt h than root grm;th while root distribution was unaffected by either the quant i ty of water app l ied or by water salinity. The effects of salinity on pl ant growth were reduced in the presence of l imi ting moisture. The specific nodul e act ivi t y (mmol c2H4/hr/g) of water s tressed alfalfa pl ants was enhanced by increasing the quantity of wat er applied a t each irriga t ion and was adversely effected by increased irrigation water salinity . In contrast, both nodulation and nodule growth were insensitive t o salt stress and sensi tive only to severe mo i s ture s tress . Alfalfa plants continued to exhibit acetylene reducing capacity at the third harvest even under severe moisture and salt stress. The species apparently continues to fix nitrogen even though environmental stress is quite substantial.

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