The Effects of Phosphate Solubilizing Rhizobacteria on Soybean (Glycine max. L.) Plants Grown under Insoluble Phosphate Fertilization Vladimir ROTARU* Institute of Genetics, Physiology and Plant Protection, Chisinau, Republic of Moldova * corresponding author: rotaruvlad@yahoo.com Bulletin UASVM series Agriculture 73(2)/2016 Print ISSN 1843-5246; Electronic ISSN 1843-5386 DOI 10.15835/buasvmcn-agr: 12395 Abstract. The aim of this study was to assess the comparative efficacy of two phosphorus solubilizing rhizobacteria namely Burkholderia cepacia B36 and Enterobacter radicincitans D5/23T combined with insoluble phosphates in soybean (Glycine max. L.). Inoculated plants were grown in sand culture under controlled greenhouse conditions. All the inoculated treatments showed better plant growth and nutrient uptake when compared to uninoculated control. The inoculation with B. cepacia performed better than with E. radicincitans. Phosphorus concentrations in shoots and roots did not change significantly at the early stage of plant growth. However, the bacterial inoculation had better stimulatory effect on phosphorus uptake by soybean fertilized with insoluble phosphates, in particular in treatment with combined application of both bacteria strains. Key words: Glycine max., growth, insoluble phosphate, PGPR Introduction. Natural rock phosphates and other phosphorus (P) amendments have been recognized as valuable alternatives to P fertiliz- ers, but nutrient efficiency of these sources is very poor. The assimilation of fixed soil P as well as hardly soluble phosphates through the use of microorganisms is an option to augment the avail- ability of P in easily available form by the crops (Poonamgautam et al., 2003). The use of benefi- cial soil microorganisms could reduce the amount of fertilizer input by increasing the efficiency of nutrient availability and other plant growth pro- moting activities. It was reported that the bacte- rial genera Burkholderia (Fankem et al., 2006) and Enterobacter (Kery et al., 2013) are the most pow- erful P solubilizers. A sand pot experiment was conducted to study the effects of Burkholderia ce- pacia and Enterobacter radicincitans inoculation on plant growth and nutrition under insoluble P fertilization. Aims and Objectives. Plant growth-promot- ing rhizobacteria (PGPR) can contribute signifi- cantly to plant nutrition and thus may help to re- duce chemical inputs in agricultural systems. The objective of the study was to assess the efficacy of two rhizobacteria Burkholderia cepacia B36 and Enterobacter radicincitans D5/23T combined with insoluble phosphates in soybean vegetative growth and nutrition. Materials and Mmethods. The sand culture experiment was conducted under controlled con- ditions. The insoluble phosphate (Ca 5 P 3 HO 13 ) was mixed with sand at a dose of 200 mg per kg be- fore planting. Bacteria inoculation was performed by soaking the seedlings with the suspension of Burkholderia cepacia B36 and Enterobacter radicincitans D5/23T separately or their combi- nation. Four treatments were arranged including control insoluble phosphate without inoculation (Ca-P), Ca-P+Burkholderia cepacia (Ca-P+B), Ca- P+Enterobacter radicinutians (Ca-P+E) and their combination (Ca-P+B+E). The plants were irrigat- ed with Hoagland solution without phosphorus and harvested in the stage of the first true trifo-