Response of Rhizobium-Faba Bean Symbiosis System to Rhizobacterial Inoculation and Arbuscular Mycorrhizal Fungi under Graded Levels of Natural Rock Phosphate in Sandy Soil

Abstract

Two field trials were conducted during two winter growing seasons of 2016/2017 and 2017/2018, using drip irrigation system. The target of this study was to evaluate the response of Rhizobium-faba bean symbiosis system to rhizobacterial inoculation (Serratia marcescens and Bacillus megaterium) and AM-fungi under graded levels of natural rock phosphate (15,30 and 45 kg P 2 O 5 /fed).The experimental design was arranged in a completely randomized block design with four replicates. The number and dry weight of nodules, N 2-ase activity, plant height, dry weight of shoot and their contents of N, P and K ,the number of pods plant-1 and the number of seeds pod-1 as well as 100-seed weight, the biological yield, seed yield and seed crude protein percentage were evaluated. The study was also concerned with the impacts of such microbial inocula and rock phosphate on dehydrogenase and phosphatase activities in soil rhizosphere. The obtained results elicited that the uninoculated plants were poorly nodulated. While, inoculating faba bean seeds with efficient Rhizobium exerted great improvement in nodulation status and N 2-ase activity. The microbiological properties of rhizosphere soil, which expressed by dehydrogenase enzyme activity and the activity of phosphatases displayed higher response to applied biofertilizers. In fact, the splendid effect was observed with the use of inoculation approach (mixture of Rhizobium, Serratia, Bacillus and AM-fungi), which caused promotive impression in nodulation, the activity of rhizosphere soil enzymes, plant growth aspects and all faba bean yield charactersin relative to other combinations or plants inoculated with Rhizobium only. Irrespective of inoculation, there is an increase in nodulation status, all vegetative growth characters, the activity of rhizosphere soil enzymes and faba bean yield with increasing natural rock-phosphate rate from 60 to 180 kg/fed(15 to 45 kg P 2 O 5 /fed).Hence, data confirmed the superiority of treatment comprising (Rhizobium conjugated mixture of PGPR's and AM-fungi)in combination with 30 or 45 kg P 2 O 5 /fed, which surpassed the other tested combinations and caused a significant augmentation in all studied faba bean parameters. While, inoculation with Rhizobium combined with PGPRs or AM-fungi and fertilized with 45 kg P 2 O 5 /fed came in the second rank. Obtained findings displayed a considerable evidence that inoculation of faba bean seeds with Rhizobium combined with a mixture of rhizobacteria may revealing a good practice for improving faba bean growth and yield characters and leading to healthier food, particularly when this practice supported by effective AM-fungi and natural rock phosphate (30 kg P 2 O 5 /fed).