Soybean Seed Coinoculation with Priestia megaterium ILBB592 and Bradyrhizobium elkanii Increases the Efficiency of Phosphorus Fertilization and Modulates the Rhizospheric Bacterial Community in the Field

Technologies that improve phosphorus (P) use efficiency in crops can reduce P fertilization needs and P losses, enhancing sustainability. This study evaluated the coinoculation of soybean seeds (cv. INIA Genesis 5602) with Bradyrhizobium elkanii and two P-mobilizing plant growth-promoting rhizobacteria (PGPR), Priestia megaterium ILBB592 and Bacillus pumilus ILBB44, formulated as biofertilizers. Field trials were conducted over two years with and without P fertilization. Coinoculation with ILBB592 improved P, N, and K uptake and the shoot dry weight regardless of P input, while ILBB44 increased the nodule dry weight. Both PGPR increased rhizospheric bacterial diversity and predicted P cycling gene abundance, especially ILBB592. Phosphorus agronomic efficiency rose when P fertilization was combined with either PGPR. Overall, coinoculation with P. megaterium ILBB592 consistently enhanced plant performance under both P regimes, highlighting its potential to sustainably reduce fertilizer use.