This season many growers will invest in fertilisers and for growers who have experienced great crops, fodder or livestock production, there will be a need to replenish soil nutrients.

When it comes to applying phosphorus to soils there are numerous fertilisers available. At BioAg our range of natural phosphate fertilisers are based on our microbially digested reactive phosphate rock – BioAgPhos.

How does BioAgPhos compare to other products?

In comparison to other RPR or Soft Rock products in the Australian market, BioAgPhos is the most reactive, has one of the higher P levels and is very low in iron and aluminium.

The release of P from BioAgPhos occurs as plant acids decompose its mineral structure and the organic (composted) matter within BioAgPhos, into plant-available forms. While 100% of the P in BioAgPhos is bio-available, around one-third is available in the short term, and the balance is released over time based on soil conditions, length of growing season, and size of the root zone.

Losses and lock-up are a hidden cost of P fertilisers but can be combatted through your choice of fertiliser. Even in the most productive soils, with high organic matter, losses of P are experienced. These losses can be due to run-off from the topsoil, leaching through the root-zone, or lock-up by soil antagonists.

Water-soluble P fertilisers readily dissolve and are transported soil-p/ (or via the QR code). in run-off or can percolate through and out of the root zone. Watersoluble P is also immediately available to plants, soil matter and soil antagonists (such as iron, aluminium and calcium in calcareous soils). Plants are relatively slow to take up P while soil antagonists can lock up P quickly such that plants cannot access or can only access this P at very slow rates.

BioAgPhos is decomposed within isolated pockets in the rhizosphere. The nature of P release means losses to antagonists are reduced as P is released to plants through the season. In addition, BioAgPhos is much less susceptible to run-off and will not percolate through the root zone.

Understanding your soil and crop needs is key to deciding the best form(s) of P to use. Research has shown that in the year of application as little as 30% of P applied is utilised. When making your fertiliser decision consider the true cost; if half of the watersoluble P you apply is locked up or lost then the true cost is twice what you believe it to be.

How much Phosphorus do I need to use?

To determine your needs, begin with a soil test. P in soils is available in different forms or ‘pools’. This includes watersoluble, in organic matter, as a mineral (such as BioAgPhos), and attached to soil antagonists. While Colwell P is commonly used, it is not suited or correlated for measuring all ‘pools’ of P available to plants, in particular RPR pools of P.

To assess your P needs incorporate a Bray 1, PBI (phosphate buffering index), and if possible, a Bray 2 analysis in your soil test.


BioAgPhos is a proven source of sustained-release P, ideal in permanent plantings and pastures. In cropping situations BioAgPhos should be supplemented with a starter fertiliser, at around one-third of typical rates, to ensure crops have access to P in the early stages of growth.

When transitioning highly productive pasture from watersoluble fertilisers to BioAgPhos we may recommend a year or two where both products are applied prior to full conversion to BioAgPhos.