ENHANCEMENT OF NITROGEN FIXATION, GROWTH, AND PRODUCTIVITY OF BRADYRHIZOBIUM-LUPIN SYMBIOSIS VIA CO-INOCULATION WITH RHIZOBACTERIA IN DIFFERENT SOIL TYPES

The current investigation was conducted in two different soil types (sandy and clay loam) at Ismailia and Sids Research stations, Agricultural Research Center, Egypt. The target of this study was to evaluate the promotive effect of various rhizobacterial co-inoculants for enhancing the nodulation, growth and productivity of lupin plants grown in the two different soil types. At preliminary, some plant growth promoting properties could be exerted by the tested rhizobacteria were examined under in vitro conditions. Afterwards, field trails were conducted at Ismailia and Sids sites during the two consecutive seasons of 2005/2006 and 2006/2007.
                Results of in vitro examination revealed that all tested rhizobacteria had a positive impression for exhibiting the PGP-properties, with clear superiority of Pseudomonas and Serratiafor producing IAA. In other side, Bradyrhizobium and Bacillus megatherium failed to excrete cyanid or siderophores.
                Results of field trials exerted that sole inoculation of lupin seeds with bradyrhizobia resulted in significant increases in nodulation status, dry matter and total N content of the plants either grown in sandy or clay loam soils after 75 days of planting during the two studied seasons. However, these parameters were significantly enhanced when the lupin plants co-inoculated with bradyrhizobia and any of the tested rhizobacteria in both investigated soils at the two studied seasons. Additionally, lupin yield and it's attributes gave the same tendency as a result of enhancement of nodulation, plant vigour and nitrogen fixation performance. For instance, the highest values of percentage increase attained in seed yield of lupin plants grown in sandy soil were 47.46% due sole inoculation with bradyrhizobia, then these values raised to range from 75.36 to 99.33% as function of co-inoculation with various rhizobacteria, during season of 2005/2006.
                The corresponding values attained for clay loam soil were 39.35% and 59.69 to 73.13%, respectively. Moreover, results exhibited that nodulation status and productivity of lupin plants grown in sandy soil (Ismailia site) exerted high responses to sole or/and co-inoculation approaches rather than these grown in the clay loam one (Sids site).