Introduction
After cereals, oilseed crops are the second most important source of energy and edible vegetable oils for human populations worldwide. In many countries, including those that rely heavily on imported edible oils, increasing the production of oilseed crops such as soybean is of strategic importance for improving food security and reducing import dependency. Phosphorus is the second most limiting essential nutrient for plant growth after nitrogen. However, a substantial proportion of phosphorus applied as chemical fertilizer becomes fixed in the soil and unavailable for plant uptake, thereby reducing fertilizer use efficiency. One practical and environmentally sustainable approach to improving phosphorus availability is the application of phosphorus biofertilizers, such as phosphate-solubilizing microorganisms and arbuscular mycorrhizal fungi, which enhance phosphorus solubilization and uptake by plants.
Materials and Methods
This study was conducted to evaluate the effect of mycorrhizal fungus, inoculation of phosphate biofertilizer on growth and consumption of phosphorus chemical fertilizer in Parsa soybean in 2019 at the research farm of Yasouj University located in Dashtrom. This study was conducted to evaluate the effect of mycorrhizal fungus, inoculation of phosphate biofertilizer on growth and consumption of phosphorus chemical fertilizer in Parsa soybean in 2019 at the research farm of Yasouj University located in Dashtrom. The experiment was conducted as a factorial based on randomized complete blocks with three replications. The experimental treatments consisted of four levels of phosphorus chemical fertilizer (triple superphosphate): 0, 60, 120, and 180 kg. ha⁻¹, and four levels of biological phosphorus fertilizer: no biofertilizer (control), phosphate biofertilizer containing Pseudomonas bacteria, mycorrhizal fungus (Glomus mosseae), and the combined application of phosphate biofertilizer and mycorrhizal fungus
 Results and Discussion
The results showed that the interaction between chemical phosphorus fertilizer and phosphorus biofertilizer significantly affected the leaf area index (LAI). The application of 180 kg ha⁻¹ of chemical phosphorus fertilizer combined with inoculation of phosphate-solubilizing bacteria and mycorrhizal fungi increased the LAI by 112.61% compared with the control. Inoculation with phosphorus biofertilizers significantly increased nutrient concentrations in both shoots and seeds. The greatest increases in nutrient concentrations were observed with the combined application of phosphate-solubilizing bacteria and mycorrhizal fungi, whereas the control treatment recorded the lowest values. The interaction between chemical phosphorus fertilizer and phosphorus biofertilizer also had a significant effect on seed yield. The highest seed yield (2,085 kg ha⁻¹) was achieved with the application of 180 kg ha⁻¹ of triple superphosphate combined with inoculation of phosphate-solubilizing bacteria and mycorrhizal fungi, whereas the lowest seed yield (971 kg ha⁻¹) was recorded in the treatment without chemical phosphorus fertilizer or biofertilizer (control). Furthermore, phosphorus use efficiency decreased as the rate of chemical phosphorus fertilizer increased. At the application rate of 60 kg ha⁻¹ of triple superphosphate, inoculation with phosphate-solubilizing bacteria and mycorrhizal fungi significantly improved phosphorus use efficiency compared with the other biofertilizer treatments, resulting in a 38.17% increase over the control.
Conclusion
Therefore, this study demonstrated that the application of phosphorus biofertilizers, including phosphate-solubilizing bacteria and mycorrhizal fungi, enhanced vegetative growth, seed yield, oil yield, and phosphorus use efficiency in soybean. However, as the application rate of chemical phosphorus fertilizer increased, the effectiveness of the biofertilizers declined significantly.