Growing Possibilities, A blog by XiteBio | Inoculants – Beyond Nitrogen Fixation? What’s That?
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Inoculants – Beyond Nitrogen Fixation? What’s That?

Any pulse or soybean grower will be familiar with bacterial inoculants: nitrogen (N)-fixing bacteria that make a symbiosis with your plant roots, form nodules and provide N to your crop. But N-fixing bacteria are not the only biological crop input out there, and legume crops are not the only ones who can benefit from these ag-biologicals. On this week’s edition of growing possibilities, we will discuss how biologicals beyond N-fixing bacteria can help all of your crops reach their maximum performance & yield potential.

Nitrogen fixing bacteria as legume crop inoculants is a centuries-old technology that has established its own niche in the ag-biological sector. There is another group of ag-biologicals that are getting lot of attention now-a-days: PGPR (Plant Growth Promoting Rhizobacteria). PGPR refers to bacteria that live in the rhizosphere of a plant whose activity has a beneficial effect on the growth or health of that plant. The term rhizobacteria refers to bacteria that colonise plant roots or live within the rhizosphere, which is the portion of soil that lies directly in the reach of a plant’s root system (1). PGPR include the N-fixing bacteria found in traditional inoculants, but also includes bacteria that can do a lot more and are not restricted to only legume crops.

For example, Bacillus bacteria are utilised for their robust modes of action in biologicals like XiteBio Yield+ and are used to enhance soil quality and plant health. These bacteria do not form nodules like the N-fixing species do, but colonise the surface of a plant’s roots and promote growth and plant health by other means. For XiteBio Yield+, these modes of action include phosphorous solubilisation, phytohormone production and production of iron chelating siderophores.

Plant hormones, or phytohormones, aid in the early development of plant roots & tissues and make nutrient acquisition by young plants easier. By having bacteria produce an abundant amount of phytohormones in the rhizosphere of developing plants, plants will emerge sooner, develop quicker and respond to environmental stress better than those that don’t.

If you are farmer, you know how important is to be on top of your phosphorous (P) fertilizer management. Over 50% of your applied fertilizer phosphates get fixed in the soil and thus remain unavailable to the crops. Bacteria like Bacillus make these fixed phosphates available to the plant for uptake. These are called phosphate solubilizers. Phosphate solubilizers (e.g., Bacillus firmus) break the bonds between phosphates in the soil and soil particles that bind to them and lock them up, taking phosphates that are unavailable to plants and turning them into forms plants can use. This not only increases the efficiency of fertilizers you apply to the field, it also creates more plant available P from the natural phosphate reserves present in the soil.

Incorporating a PGPR biological into your crop fertility plan can increase the ROI of your phosphate fertilizer investment, improve the early development of your crop and ensure that your plants get the nutrients they need from the soil as easily as possible. Utilising a PGPR biological and an inoculant containing N-fixing rhizobia is a great way to give your crop the best chance in the field. Next season, don’t miss your opportunity to let natural soil bacteria do their work for you!


1) Banerjee, M.R., Yesmin, L., Vessey, J.K. 2006. Plant-Growth-Promoting-Rhizobacteria As Biofertilizers and Biopesticides. In: Handbook of Microbial Biofertilizers. Haworth Press: New York, London, Oxford. pp. 137-181.

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