New fertiliser passes the test

Fert Options
with Robin Boom
Agronomic Advisory Services

Early-2019 I was approached by the owners of Australian fertiliser company Fert Direct PTY Ltd, which market a sulphur-infused triple superphosphate called Triple Plus that they were keen to sell here. They claimed it out performed superphosphate in trials in Australia, which they believed was due to the very fine elemental sulphur that is below 35 microns in particle size contained in each granule.

To convince me of its worth they were prepared to fund a small trial on my own property at Taumarunui, comparing it against other commercially-available phosphate products. With a number of newer fertiliser products coming onto the market in the last three-to-four years, I thought it was a great opportunity to trial some of these. So I ended up comparing Triple Plus with standard superphosphate, Triple Super/Sulphur, Replenish and DCP 18 (both higher analysis dicalcium phosphates), and three RPR products – granulated RPR, Sechura RPR, and Algerian RPR.

The trial ran from June 2019 to June 2020 with four replicates for each treatment applied at the equivalent of 45kg P and 30kg S/ha. The top four treatments were the Triple Plus, Superphosphate, Replenish and Sechura, which grew just under 10 tonne of dry matter – all within about 200kg DM of each other. The DCP18 was about 500kg DM behind these, and the Triple Super/Sulphur and Algerian RPR about 1000kg of dry matter behind.

The granular RPR was 1000kg DM behind these two, at just under eight tonnes, and the control was 7350kg DM. The upshot was that the site was very P responsive, and most products performed as expected, but there were some surprises.


I was surprised that Sechura RPR in the first year was as productive as the superphosphates. I was also surprised how well Algerian performed, and how poorly the granulated RPR performed. The poor performance of the triple super is – in my opinion – an anomaly because it would normally be expected to perform as good as the other water-soluble P products. Why the granulated RPR performed so poorly I suspect could be due to the high concentration of fine RPR powder, which when broken up on the soil surface has a mild liming effect that mops up the free acids in the vicinity, slowing down the release of the phosphate. As the granules are quite large (3mm-4mm), if they were smaller, say a 1mm-2mm prill, then I suspect it will work faster – and so I have suggested to the importer that they try and change this.

The Australian company is now trading in New Zealand as Inphos, and working out of Marsden Agri’s depot at Waharoa, and from Hastings out of Rorison’s depot there. Their Triple Plus product on my property worked out the most economic per kg DM grown on my property once cartage and spreading costs were factored in (8.5c), followed by straight super (9.6c), followed by Sechura RPR (10c), followed by DCP 18 (12.9c), followed by Replenish (13.1c), followed by Triple Super (13.3c) followed by Algerian RPR (14.3c) followed by Granular RPR (23.6c).

However I need to stress that with only four replicates, this trial could be a statistical headache as there is a lot of ‘noise’ from animal influences such as dung and urine as it is being grazed in situ.

In soil scientist Doug Edmeades’ latest Fertiliser Review (May 2020, Number 43) he commends the introduction of Triple Plus as real competition for Ravensdown and Ballance’s superphosphate. It costs $610/tonne ex-Waharoa and is twice as concentrate as standard superphosphate.

This spring

This spring Inphos is also bringing in Sulphate of Ammonia and MAP (Mono Ammonium Phosphate), which is a very popular fertiliser used in Australia. MAP is internationally traded around the globe, and historically has been sold here in NZ as Ammophos MAP. It is the highest P fertiliser, at 22-23 per cent, compared to DAP and Triple Super which are 20 per cent, and also has 10-11 per cent N. Ravensdown list their MAP at just under $900/tonne, so it’s been off the radar for most people at that price. Inphos will be selling it for around $200/tonne cheaper. It is 2.5 times more concentrate than standard superphosphate, so at their price, even excluding the cartage and spreading savings, you get all the nitrogen for free on a straight per unit of P basis.

Disclaimer – these are the opinions of independent agronomy and soil fertility consultant Robin Boom, of Agronomic Advisory Services. Any decisions made should not be based on this article alone and appropriate professional assistance should be sought. Robin Boom, CPAg, is a member of the Institute of Professional Soil Scientists. Ph: 0274448764. Email:


There are no comments on this blog.

Leave a Comment

You must be logged in to make a comment. Login Now
Opinion Poll

We're not running a poll right now. Check back soon!