Phosphorus (P) is the second important key plant nutrient after nitrogen. An adequate supply of P is therefore required for proper functioning and various metabolisms of plants. Majority of P in soils is fixed and hence, plant available P is scarcely available despite the abundance of both inorganic and organic P forms in soils. A group of soil microorganisms capable of transforming insoluble P into soluble and plant accessible forms across different genera, collectively called phosphate-solubilizing bacteria (PSB), have been found as best ecofriendly option for providing inexpensive P to plants. These organisms in addition to supplying soluble P to plants also facilitate the growth of plants by several other mechanisms, for instance, improving the uptake of nutrients and stimulating the production of some phytohormones.
Two field experiments were conducted at EL-Gemmiza, Agric. Res. Station,(30º 47׳ 22.5״ N, 31° 07׳ 34״ E, elev. 10 m), Agric. Res. Centre., El-Gharbia Governorate, Egypt, during the two successive summer seasons of 2017 and 2018, to study the effect of different application sources and rates of phosphorus on the growth, productivity, yield characters and quality of soybean (Glycine max L.), c.v. Giza 111. The treatments consisted of four sources of phosphorus [single super phosphate (SSP), rock phosphate (RP), single super phosphate (SSP) + phosphate solubilizing bacteria (PSB) and rock phosphate (RP) + phosphate solubilizing bacteria (PSB)] at three levels of added P.i.e (0, 15 and 22.5 kg P2O5 fed-1).Results revealed that seed and straw yield and uptake of N, P and K increased significantly with both sources of P over control. Application of single superphosphate proved superior increases compared to rock phosphate in respect of yield and uptake of nutrients. There was a significant increase in yield and uptake of nutrients with increase in P application rate from 15 kg P2O5 fed-1 to 22.5 kg P2O5 fed-1 applied either as SSP or RP. Protein content in soybean seed increased significantly with both the sources of P.The application of SSP +PSB (T9) recorded higher yield (grain and straw) and uptake of nutrients than phosphorus alone. The maximum seed (1572 kg/fed) and straw (4473.33 kg/fed) yields were recorded with 22.5 kg P2O5 fed-1 as SSP+PSB. Significant differences among the treatments were noticed with respect to number of pods per plant, seed yield per plant, test weight and seed yield. Application of 22.5 kg P2O5 fed-1 with PSB (T9) produced maximum number of pods/plant (150.67), seed yield (74.23 g/plant) and hundred seed weight (18.77 g/plant) as SSP and the lowest was in the control. Regarding evaluation of phosphorus use efficiency had more pronounced effects on combined application of SSP+PSBfollowed by RP+ PSB. Quality parameters viz., oil content, oil yield and crude protein content differ markedly among different treatments with the application of levels of phosphorus and bio-fertilizer.