Abstract
A pot experiment to compare the acidity tolerance and symbiotic nitrogen fixing capacity among 11 varieties of alfalfa (Natsuwakaba, El unico, Williamsburg, Du Puits, Arizona common, Saranac, Common, Rhizoma, Caliverde 65, Aichi 10 and Moapa) was made with an acidic mineral soil (pH 5: unlimed soil) and the same soil adjusted to pH 7 with CaCO_3 (limed soil). Plant yield, nodulation, plant total nitrogen and nitrogen fixing capacity with acetylene reduction method were measured. The results obtained were as follows. 1. Plant yield of any variety grown at the unlimed soil was lower than that grown at the limed soil though there appeared slight differences among varieties. 2. In acidity tolerance of varieties grown at the unlimed soils on the basis of plant yield, Caliverde 65, Saranac and Moapa were relatively high whereas Common and Du Puits were low. 3. On the other hand, comparatively high acidity tolerance was shown in Rhizoma, Natsuwakaba and Saranac on the basis of relative plant yield of unlimed plots to that of limed plots while El unico and Arizona common were low. 4. Soil acidity had a more adverse effect on the nodule formation and symbiotic nitrogen fixation than on the root growth. 5. As the symbiotic nitrogen fixation system was damaged intensively under acidic soil conditions, it is recommended to apply nitrogen fertilizer moderately to grow alfalfa under those conditions.
