Inoculation and nitrogen availability is important for rapid establishment of Medicago varieties. Ten alfalfa varieties were grown under controlled environmental conditions, in post
containing coarse river sand, to determine the effect of inoculation and different amounts of nitrogen (0, 0.5, 1.25, 3.12 , 5 mM pure ammonium nitrate) on the growth and nodulation of
alfalfa cuItivars. The experimental design was a split - polt one with a 10x 15 factorial arrangement and 3 replications. Uninoculated cultivars, which received N free nutrient solution failed nodulation and development. Seventy five days after sowing, traits such as nodulation, dry matter and N concentrations were determined in inoculated plants. Results of the experiment revealed that: (1) For all cultivars, shoot and root dry weight at 0.5 -mM (starter nitrogen) being significantly higher than without nitrogen sample or control, (2) all varieties showed marked inhibition of nodulation development with 5mM nitrate treatments, as compared with respective 0.5 mM starter N. This indicated that starter nitrogen is necessary to early growth, and efforts to overcome the inhibitory effect of nitrate on legume nodulation should possibly be concentrated further on limiting the nitrogen fertilization in legume swards.
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