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The phosphate rock used in agriculture is known by a number of names across the fertiliser industry, including Reactive Phosphate Rock (RPR), Direct Application Phosphate Rock (DAPR), Mineral Phosphate, Soft Rock, Hard Rock and other variations.

What is phosphate rock?

Phosphate rock is a natural mineral. The phosphate component of the mineral is present in the form of apatite – a mineral lattice.

About 95% of the known global phosphate resource is sedimentary rock, formed from marine life deposits in ancient seabeds. Most people have heard about phosphate rock formed from guano, such as the rock mined at Nauru. However these deposits have declined and their output is low.

Can Phosphate Rock be used as a fertiliser?

The right phosphate rock, used effectively, is an excellent source of long lasting and non-polluting phosphates.

The quality of phosphate rock and its suitability for use as a fertiliser varies from deposit to deposit and may also vary within a single deposit.

There may be variation in how well the phosphate is bound within the rock, and also the amount of elements including trace elements, heavy metals, radioactive isotopes, calcium, carbonate, fluorine and silica.

Laboratory analysis or field trials are the most effective way to test the ability of phosphate rock to release nutrient, and their effectiveness as a fertiliser

Is phosphate rock ‘organic’?

Being a natural mineral, phosphate rock is commonly sold and promoted as an organic product. Being organic does not guarantee the effectiveness of phosphate rock as a source of nutrient, i.e. a fertiliser.

To measure the effectiveness of rock phosphate as a fertiliser, industry bodies and governments across the world have tried to define the chemical properties of phosphate rocks (typically RPR) used as fertilisers.

In New Zealand reactive phosphate rock (RPR) is a commonly known and used phosphate rock fertiliser. To be able to sell phosphate rock as RPR in New Zealand it must meet a number of parameters, including a minimum P content of 10% with a minimum of 30% of the total phosphorus soluble in a defined citric acid test.

There is no standard in Australia that phosphate rock must meet when being used as a fertiliser. However, since 2001 BioAg has been evaluating the phosphate rocks available to us. Our selection of rock is based on a number of criteria but most importantly is the reactivity of the rock (as measured in a laboratory) and its successful performance in the field, both in Australia and around the world.

The availability of phosphorus determines effectiveness

While phosphate rock is commonly defined by the total amount of phosphorus or P, it is the availability of the phosphorus that will determine the product’s effectiveness as a fertiliser.

When assessing phosphorus availability the most important aspect is to ensure you use a laboratory that is capable of analysing phosphate rocks. Soil and mineral laboratories may not use the correct methods. Comparing analysis results of different RPR products from the same laboratory is always best.

A laboratory will commonly determine phosphorus release by testing solubility in dilute citric acid and dilute formic acid.

The results can be provided as %P or as a % of Total P.

In addition there is a plant availability test which will analyse for the amount of phosphorus that will become plant available over time.

How is phosphate content in RPR measured?

The three common ways to measure phosphate content in phosphate rocks are:

  • phosphorus (%P)
  • phosphate (%P2O5)
  • %BPL (% Boned Phosphate of Lime)

Conversion:

  • 1% P = 2.2915% P2O5
  • 1% P2O5 = 2.1852% BPL

Example: A product that contains 12.6% P has the same amount of phosphorus as one with 28.9% P2O5

What about BioAg’s products?

BioAg’s products are manufactured using high grade, highly reactive Algerian phosphate rock. After adding our proprietary phosphate digester, with its blend of microbes and microbial food, BioAgPhos composts for between 14 to 20 days before it is ready for sale.

BioAgPhos has been laboratory tested and used in a number of replicated trials to prove its value as a fertiliser.

BioAgPhos bulk pile and conveyor
Processing BioAgPhos at our Geelong facility

BioAgPhos provides the P your farm needs

Want to know if a BioAg program including BioAgPhos will give your crops or pasture the P it craves? Talk to one of our qualified and experienced area managers. They’d be delighted to assist.

Further reading

McLaughlin M. J. , Fleming N. K. , Simpson P. G. , Bolland M. D. A. , Gilkes R. J., Sale P. W. G. , Blair G. J. , Hepworth G. , Gilbert M. A. , Stewart J., Garden D. L. , Dann P. R. , Hamilton L., Hunter J. , Cayley J. W. D. , Ward G. N. , Johnson D. Lewis D. C. (1997) National Reactive Phosphate Rock Project —aims, experimental approach and site characteristicsAustralian Journal of Experimental Agriculture 37, 885-904. 

Read the abstract

Fertiliser Standards Australia National Code of Practice for fertiliser labelling and warnings

Peir K. Pufahl, Lee A. Groat Sedimentary and Igneous Phosphate Deposits: Formation and Exploration: An Invited Paper Economic Geology (2017) 112 (3): 483-516.
Read the abstract

Phosphate Rock Factsheet on the NSW Government Resources & Geoscience website

A report on varying rocks at the New Zealand Journal of Agricultural Research
A. G. Sinclair , P. D. Johnstone , J. H. Watkinson , L. C. Smith , J. Morton & A. Judge (1998) Comparison of six phosphate rocks and single superphosphate as phosphate fertilisers for clover‐based pasture, New Zealand Journal of Agricultural Research, 41:3, 415-420, 
Read the abstract

Németh, T & Magyar, Marianna & Csathó, Péter & Osztoics, E & Baczó, G & Holló, S & Németh, I. (2002). ‘Long-term field evaluation of phosphate rock and superphosphate use strategies in acid soils of Hungary: Two comparative field trials.’ Nutrient Cycling in Agroecosystems. 63. 81-89. 10.1023/A:1020529001629.
Read the abstract

Read more about the role of reactive phosphate rock fertilisers in Australia

BioAg products using reactive phosphate rock

BioAgPhos

12.7% P | 35% Ca | 1% S
41% citric soluble, 73% formic soluble
Highly reactive, high-grade reactive phosphate rock (RPR) combined with BioAg’s microbial digesting agent.

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BioAgPhos S10

P 11.4% | S 10% | C 32%

Provides elemental sulphur in the form of sulphur bentonite; a sustained release form of sulphur for the entire growing season. Ideal for higher rainfall and higher leaching environments.

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BioAg Superb

P 8.4% | S 6.8% | Ca 31%

Highly reactive, high-grade reactive phosphate rock (RPR) combined with BioAg’s microbial digesting agent and gypsum. Ideal for soils that need sulphur, phosphorus and calcium.
Suited to pastures/grazing, and crops needing extra sulphur (such as canola).

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MagPhos

P 6% | S 5% | C 28% | Mg 4.8%
Highly reactive, high-grade reactive phosphate rock (RPR) combined with BioAg’s microbial digesting agent and magnesite. Ideal for soils low in magnesium and phosphorus where risk of grass tetany is present.

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Pasture Primo

P 3.7% | S 0.3% | Ca 37%
Highly reactive, high-grade reactive phosphate rock (RPR) combined with BioAg’s microbial digesting agent. A source of calcium through the increase of the lime component in the blend. Designed for soils lacking calcium and phosphorus.

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PotPhos

Available with Muriate of Potash (MoP) or Sulphate of Potash (SoP) Highly reactive, high-grade reactive phosphate rock (RPR) combined with BioAg’s microbial digesting agent and potassium sulphate (sulphate of potash) in a ratio of 3:1. Suited to all grazing systems where potassium (K) inputs are needed.

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Read stories of growers who have reaped the benefits of using BioAgPhos

Rely on BioAg’s RPR knowledge and experience

At BioAg we understand Reactive Phosphate Rock. We know what works and what doesn’t.

Phosphate rocks have very different suitability for direct applications. If you want to use long lasting and non-polluting phosphates, talk to a BioAg agronomist, and consider BioAgPhos. Depending on your soil’s nutrient requirements, BioAgPhos can be blended with other nutrients, at source or on farm, to optimise the nutrient package for your soils and plants.

The RPR we use in our products performs reliably across a wide spectrum of soils and enterprise types. BioAgPhos is the long lasting P product that you can rely on, supported by considerable replicated trial based evidence.

Find your nearest BioAg area manager or specialist agronomist