Influence Of Biofertilization And Chemical Fertilizers On Soybean

Abstract

Pot and field trials were conducted to study the effects of inoculation with root - nodule bacteria (Bradyrhizobium sp.) and with vesicular-arbuscular (VA) mycorrhizal fungi, as well as the effects of fertilization with superphosphate or urea on the nodulation, dry matter yield and tissue nitrogen and phosphorus contents of soybean (Glycine max L Merril). No nodules were observed in uninoculated plants. Inoculation with different Bradyrhizobium strains resulted in differential capacities for nodulating soybean and for improvements in dry matter production and tissue nitrogen and phosphorus contents. Likewise, VAM inoculation increased nodulation, dry matter yield and tissue nitrogen and phosphorus contents, particularly in the presence of superphosphate fertilization. Dual inoculation with both Bradyrhizobium and VAM fungi revealed synergistic effects due to the dual symbiosis. Watering at the rate of 40 L/m2/week resulted in higher nodulation and dry matter yield as compared to watering at the rate of 20 L/m-/week, particularly in the presence of VAM inoculation and phosphorus fertilization. Addition of phosphate fertilizer at the rate of 50 kgP2O5/ha enhanced nodulation, dry matter yield and tissue nitrogen and phosphorus contents, but depressed the rate with which VAM fungi infected soybean roots. When Bradyrhizobium inoculation was coupled to urea fertilization at the rate of 60 kg/ha, dry matter yield and tissue nitrogen contents were improved, but nodulation was completely inhibited. The present study demonstrated the practical benefits of VAM inoculation in low-input agricultural systems of the semiarid sub-tropics where mycorrhizal technology can have its greatest impact.