Studies on the Incidence of Certain Physiological Groups of Bacteria in the Rhizosphere

It has been demonstrated by the ultimate dilution method that the rhizospheres of field crops such as wheat, oats, rye, and barley harbor a bacterial population which is physiologically more active than that of non-rhizosphere soil. This was shown by use of the following criteria: reduction of methylene blue or resazurin, production of acid and gas from glucose, and ammonifying and denitrifying capacity. In general a higher proportion of isolates from the rhizospheres of wheat, barley, and rye were capable of reducing methylene blue, producing acid from glucose, and producing ammonia from peptone than from control soil. The significance of these and the above results is discussed.