Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/1995
Publication Date: N/A
Interpretive Summary: Alfalfa is one of the main forage crops in Pakistan and is grown widely under both natural rainfed and irrigated conditions. Alfalfa forms a unique relationship with a soil bacteria (Rhizobium meliloti) that allows it to biologically fix nitrogen. Drought conditions imposed by uncertain and scarce precipitation or sporadic irrigation reduce biological nitrogen fixation and forage yield in alfalfa. Because both the host alfalfa plant and its associated soil rhizobia are important for alfalfa production, we conducted a greenhouse experiment to determine the effect of drought on plant dry weight and nitrogen fixation in seven rhizobial strains from Pakistan and three alfalfa cultivars. Results from this experiment indicated that three rhizobial strains (UL 136, UL 210 and UL 222) formed root nodules capable of nitrogen fixation and produced large plants under drought conditions. As a result, these three rhizobial strains may be beneficial for increasing alfalfa production under water-limited conditions in Pakistan.
Technical Abstract: The effect of drought on nodulation, biomass production and symbiotic nitrogen fixation was evaluated for seven strains of Rhizobium meliloti Dang. and three alfalfa (Medicago sativa L. and M. falcata L.) accessions. Alfalfa plants were grown for 10 weeks in plastic pots containing a sterilized mixture of sand and peat moss maintained at -0.03, -0.5 and -1.0 0MPa. Number of nodules, total plant dry weight and shoot nitrogen pool declined as drought increased from -0.03 to -1.0 MPa. Rhizobial strains varied markedly in their ability to form nodules and fix nitrogen under drought. Plants inoculated with strains UL 136, UL 210 and UL 222 formed nodules at -0.5 and -1.0 MPa and had plants with greater total dry weight and shoot nitrogen pool than plants with no nitrogen. These three rhizobial strains may be beneficial for increasing alfalfa production under water-limited conditions.