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BioAgPhos® – enhanced reactive phosphate rock (RPR) fertiliser

Why it is significantly different from just ordinary RPR or Soft Rocks.

Phosphate rock is a naturally occurring mineral that is used to manufacture water-soluble phosphate chemical fertilisers. As much of the phosphate rock mined around the world has little to modest benefit as a directly applied fertiliser, the phosphate (P) in the rock is converted to plant-available forms (typically water soluble) by reacting it with strong acids, such as sulphuric, phosphoric, nitric and others.

These strong acids break down the P present in the rock as apatite (a mineral lattice). The strength of the lattice depends on the way the rock was formed and the impurities that are present. The weaker the lattice the more reactive the phosphate rock.

In nature the highly to very highly reactive phosphate rocks can have their lattice broken down through the action of microorganisms. Many microbial organisms including bacteria, fungi, actinomycetes, and algae exhibit P solubilisation and mineralisation ability. The main roles of microorganisms in P solubilisation include (1) the release of extracellular enzymes (biochemical mineralisation), (2) the release of P during substrate degradation (biological mineralisation), and (3) the secretion of mineral-dissolving complexes or compounds (siderophores, protons, hydroxyl ions, organic acids) [i].

Soil bacteria that have been reported to mobilise P through solubilisation and mineralisation include various strains of Azotobacter, Agrobacterium, Bacillus, Paenibacillus, Pseudomonas, Ralstonia, Rhizobium, Rhodococcus, Thiobacillus [ii], [iii], [iv], [v]. In addition, approximately 20% of actinomycetes could solubilise P, including those in the genera Actinomyces, Micromonospora, and Streptomyces [vi].

Soil fungi have been reported to be able to traverse long distances within the soil more easily than bacteria and may be more important to the solubilisation of inorganic P in soils as they typically produce and secrete more organic acids than bacteria.

Some previous studies have found that several arbuscular mycorrhizal fungi (AMF), such as Rhizophagus irregulariscan also solubilise P either directly through exudation, or indirectly through modification of soil P solubilising microorganism communities [vii].

BioAgPhos® is enhancing the highly reactive natural phosphate rock by utilising the ability of microbes to solubilise P. Our proprietary phosphate digester used to inoculate the phosphate rock is formulated and brewed to contain both microbial food sources and P solubilising microorganisms. Thereby making BioAgPhos a unique and better performing natural P fertiliser.

Analysis of raw material rock phosphate and BioAgPhos has shown that BioAgPhos contains P solubilising bacteria not present in the raw material rock phosphate. This includes around 80 bacteria and 30 fungi species [viii].

Among those identified were species from genera known for solubilising P, as well as nutrient cycling in soils and plant growth-promotion; Acinetobacter, Agrobacterium, Agromyces, Algoriphagus, Azorhizophilus, Bacillus, Microbacterium, Micrococcus, Pseudomonas, Rhizobium, Rhodococcus, Streptomyces.

Also refer to BioAg’s White Paper on RPR explaining that not all RPR’s or Soft Rocks are the same in P content. In Australia, unlike New Zealand, there is no standard P content percentage (%) minimum requirement to be used as a fertiliser.


[i]  Sharma, S.B.; Sayyed, R.Z.; Trivedi, M.H.; Gobi, T.A. Phosphate solubilizing microbes: Sustainable approach for managing phosphorus deficiency in agricultural soils. Springerplus 2013, 2, 587. [ii]  Babalola, O. O., and Glick, B. R. (2012b). The use of microbial inoculants in African agriculture: current practice and future prospects. J. Food Agric. Environ. 10, 540–549. [iii]  Kumar, S., Bauddh, K., Barman, S. C., and Singh, R. P. (2014). Amendments of microbial bio fertilizers and organic substances reduces requirement of urea and DAP with enhanced nutrient availability and productivity of wheat (Triticum aestivum L.). Ecol. Eng. 71, 432–437. doi: 10.1016/j.ecoleng.2014.07.007. [iv]  Fernández Bidondo, L., Silvani, V., Colombo, R., Pérgola, M., Bompadre, J., and Godeas, A. (2011). Pre-symbiotic and symbiotic interactions between Glomus intraradices and two Paenibacillus species isolated from AM propagules. In vitro and in vivo assays with soybean (AG043RG) as plant host. Soil Biol. Biochem. 43, 1866–1872. doi: 10.1016/j.soilbio.2011.05.004. [v]  David, P., Raj, R. S., Linda, R., and Rhema, S. B. (2014). Molecular characterization of phosphate solubilizing bacteria (PSB) and plant growth promoting rhizobacteria (PGPR) from pristine soils. Int. J. Innov. Sci. Eng. Technol. 1, 317–324. [vi]  Sharma, S. B., Sayyed, R. Z., Trivedi, M. H., and Gobi, T. A. (2013). Phosphate solubilizing microbes: sustainable approach for managing phosphorus deficiency in agricultural soils. Springerplus 2, 587–600. doi: 10.1186/2193-1801-2-587. [vii]  Mackay J.E., Cavagnaro T.R., Müller Stöver D.S., Macdonald L.M., Grønlund M., Jakobsen I. A key role for arbuscular mycorrhiza in plant acquisition of P from sewage sludge recycled to soil. Soil Biol. Biochem. 2017;115:11–20. doi: 10.1016/j.soilbio.2017.08.004. [viii]  https://www.agrf.org.au/