A phosphate comparison

Better soils
with Brett Petersen
Kiwi Fertiliser & Golden Bay Dolomite

For the last three years phosphate trials have been conducted by Bernard Lilburn owner of Mt. View Store, near Bulls. Products compared were Sechura RPR, (SR), with sulphur added; Superphosphate (SP); Dicalcic super (D); a Kiwi Fertiliser Blend (KFB); and Control (C).

The results in order were: Kiwi Fertiliser blend, Sechura RPR, Control, Dicalcic and last was Superphosphate. Using control as the benchmark, this resulted in kg/dm/ha; KFB = +9152, SR = +8817, C = 0, D = -1629 and SP = -3488. Each year on average in kg/ha, Sechura RPR outproduced super by 4102 and Dicalcic by 2939. The Kiwi Fertiliser blend outperformed super by 4213, and Dicalcic by 3594. Kiwi Fertiliser also import and market Sechura RPR.

Stock health

We know from on-farm comparisons between Sechura and superphosphate that stock health is better when Sechura RPR is used and animal health costs are much reduced. An example with sheep is that only 25 per cent of hoggets needed dagging when run on land fertilised with Sechura RPR, while 75 per cent of hoggets needed dagging when superphosphate was used. This difference can be further widened by on-farm management practices. On properties using our soil fertility programme, animal drenches are not usual or regular and veterinary intervention is rare. Diseases such as facial eczema are almost totally absent. I have used Sechura RPR when phosphate is required, which is not often, and I have not drenched my own stock for more than 20 years. They fatten up extremely well without any chemicals. My stock agent often comments: “the stock always weigh heavier than they look”.  

Nurture microbiology

Acidic products, such as superphosphate, trend towards the anaerobic, (non-oxygen loving) disease-forming microorganism end of the spectrum. Alkaline products trend towards supporting the aerobic, (oxygen loving) non-disease forming, healthier side of the equation that needs to be encouraged to increase and nurture microbiology. It is always a mystery to me why phosphate rock is treated with sulphuric acid to become superphosphate which is applied to the land where the applied P is available for about six weeks, after which time it reverts to a more unavailable (almost locked up) form than it was before acid treatment. Bad habits are hard to break. I know of properties that have not had phosphate applied for 15 years. They are not short of phosphate.

More recently there have been other phosphate trials carried out near Taumarunui for the 12 months ending July 20, 2020. These results show a similar pattern, albeit at a lower level. In order from best to least dry matter, the results were Sechura RPR with Sulphur 90, 9907kg; Superphosphate, 9884 kg; Replenish, 9744kg; Triple Plus, 9704kg; DCP18/S90, 9306; Triple Super/S90, 8879; Algerian RPR/S90, 8759; Granular Egyptian RPR/S90, 8233; Control 7365. I do question that when phosphate is being trialled, why doesn’t the control get sulphur as well? This is typical of many trials.


These ‘oversights’ also happened with the so-called ‘national series’ where Superphosphate that contains sulphur, came out on top when compared with Sechura RPR featured above. No sulphur was added to the Sechura RPR, which should have invalidated the entire six-year trial. The trials were not invalidated so superphosphate could ‘win’. The claim was that Sechura RPR had to be mixed with other P sources when it was not true.

Disclaimer – these are the opinions of Brett Petersen, of Kiwi Fertiliser. Any decisions made should not be based on this article alone and appropriate professional assistance should be sought. Freephone Kiwi Fertiliser on 0800 549 433.


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