Pasture-Primo

Trials: Reactive Phosphate Rock

To evaluate the effectiveness of reactive phosphate rock (RPR) as a phosphorus fertiliser for pastures in Australia, trials were completed across the major pasture production areas of Australia.

The results of these trials were subsequently published in a book titled The Role of Reactive Rock Phosphate Fertilisers for Pastures in Australia.

Additional funding was then obtained for one of the trial sites at Smithton in Tasmania, and this enabled total dry matter production levels to be measured for an additional 4 years after the last application of phosphorus was applied.

The Smithton site trial compared five different reactive phosphate rocks (RPR) and single super phosphate (SSP), applied at four different application rates. The application rates were 0, 17, 34 & 68 kg/ha of phosphorus, with 17kg/ha of phosphorus simulating an annual application rate, whereas the 34 and 68 kg/ha of phosphorus simulated a capital application rate.

The site was planted to white clover, sub clover, strawberry clover, perennial ryegrass & tall fescue.

In each year, the highly reactive phosphate rocks out performed SSP at an application rate of 17kg/ha of phosphate, particularly in the first two years after the applications had ceased.

The 68kg/ha of phosphate treatment had variable results for the first four years of the trial and the difference between the two product types was not significant.

What is significant is the change in dry matter production after the application of phosphorus ceased in 1995.

It is well understood that superphosphate suffers from leaching and locking-up. This restriction on phosphorus availability resulted in the reduced yield of dry matter.

Conversely, RPR continued to produce dry matter in the years after any fertiliser was applied.

The graph included illustrates the results.

What’s the take home message?

If you produce pasture in an environment similar to this an RPR based product (like BioAgPhos) will provide a production buffer during the years when phosphate is not applied, whether that’s due to environmental conditions, poor commodity pricing, spreader availability or a shortage of available funds.

It is for this reason that a BioAg program that utilises BioAgPhos will generally include an application once every two years.

As well as having a higher amount of P/kg of product, spreading BioAgPhos along with your other inputs ends up providing some very nice savings of both time and money.