Soil fertility is one of the major limiting factors for crop's productivity in Egypt and the world in general. Biological nitrogen fixation (BNF) has a great importance as a non-polluting and a cost-effective way to improve soil fertility through supplying N to different agricultural systems. Faba bean (Vicia faba L.) is one of the most efficient nitrogen-fixing legumes that can meet all of their N needs through BNF. Therefore, understanding the impact of rhizobial inoculation and contrasting soil rhizobia on nodulation and N 2 fixation in faba bean is crucial to optimize the crop yield, particularly under low fertility soil conditions. This study investigated the symbiotic effectiveness of 17 Rhizobium/Agrobacterium strains previously isolated from different Egyptian governorates in improving the nodulation and N 2 fixation in faba bean cv. Giza 843 under controlled greenhouse conditions. Five strains that had a high nitrogen-fixing capacity under greenhouse conditions were subsequently tested in field trials as faba bean inoculants at Ismaillia Governorate in northeast Egypt in comparison with the chemical N-fertilization treatment (96 kg N·ha −1 ). A starter N-dose (48 kg N·ha −1 ) was applied in combination with different Rhizobium inoculants. The field experiments were established at sites without a background of inoculation under low fertility sandy soil conditions over two successive winter growing seasons, 2012/2013 and 2013/2014. Under greenhouse conditions, inoculated plants produced significantly higher nodules dry weight, plant biomass, and shoot N-uptake than non-inoculated ones. In the first season (2012/2013), inoculation of field-grown faba bean showed significant improvements in seed yield (3.73-4.36 ton·ha −1 ) and seed N-yield (138-153 Kg N·ha −1 ), which were higher than the uninoculated control (48 kg N·ha −1 ) that produced 2.97 Kg·ha −1 and 95 kg N·ha −1 , respectively. Similarly, in the second season (2013/2014), inoculation significantly improved seed yield (3.16-4.68 ton·ha −1 ) and seed N-yield (98-155 Kg N·ha −1 ) relative to the uninoculated control (48 kg N·ha −1 ), which recorded 2.58 Kg·ha −1 and 80 kg N·ha −1 , respectively. Interestingly, faba bean inoculated with strain Rlv NGB-FR 126 showed significant increments in seed yield (35%-48%) and seed N-yield (34%-49%) compared to the inorganic N fertilizers treatment (96 kg N·ha −1 ) over the two cropping seasons, respectively. These results indicate that inoculation of faba bean with effective rhizobial strains can reduce the need for inorganic N fertilization to achieve higher crop yield under low fertility soil conditions.

No abstract

Bacteria colonizing the rhizosphere, a narrow zone of soil surrounding the root system, are known to have beneficial effects in improving the growth and stress tolerance of plants. However, most bacteria in natural environments, especially those in rhizosphere soils, are recalcitrant to cultivation using traditional techniques, and thus their roles in soil health and plant growth remain unexplored.