Two consecutive factorial experiments were carried out during the two winter seasons 2020/2021 and 2021/2022 to study the application of Priestia megaterium inoculant, Azolla extract or compost as P-activators to reduce the inorganic phosphorus (Pi) fertilizer for the potential cultivation of faba bean in calcareous soils. The treatments were applied in a split-plot design to compare the full dose or half dose of Pi, individually and in com-bination with P-activator. The effect of applied treatments was estimated in terms of the rhizosphere biology, shoot and root metrics, nodulation status, photosynthetic pigments, nutrients uptake as well as yield and yield components. Biologically, total microbial count and phosphate dissolvers recorded increases in their numbers in response to half dose of Pi coapplied with each of P-activators, especially where they had been received com-post. Coaddition of P. megaterium, Azolla extract and compost revealed a significant improvement in vegetative growth in terms of plant height, root surface area, nodulation status and total chlorophyll. At post-harvest, esti-mated overall performance indicated variable enhancements for yield and yield components in response to P-activators with superiority of compost coaddition with P. megaterium and Azolla extract under half dose of phosphorus fertilizer to relatively emulate that attained by full dose. Accordingly, a possible reduction in P-fertilizers can be achieved using P. megaterium, Azolla extract with compost as P-activators in calcareous soil for faba bean cultivation.