Below is a passage written by Jerry Brunetti, as part of an article titled “Cows don’t have carburettors” and was published in Acres USA, May 2012. The title seems absurd; it is extremely relevant.

Unfortunately, livestock operators, especially in New Zealand, are being sold a big lie as to how to grow forages, applying huge amounts of urea and super phosphate for yield while dropping the energy levels of the forages, increasing the “funny protein” (nitrogen), obliterating the biodiversity of forbs (forage herbs) rich in phenols, carotenoids/terpenoids, and complexing those vital elements in the soil, namely calcium, magnesium, sulfur and boron that are responsible for creating quality protein and forage diversity.

Many New Zealand farms have acidic soils (e.g., pH of 5.5). Yet, their soil analysis showing a P2O5 “deficiency” was derived from an “Olsen Test,” to be used on alkaline soils. Thus these soils show a continued “need” for super phosphate, even though some soil tests that we reviewed contained 4,000 pounds per acre of phosphate when they were analysed. All of this excessive phosphate locks up whatever calcium and magnesium is present, denying the plant an ability to synthesise both quality protein and quality forage calories in the form of pectins and hemi-cellulose.

Phosphate nurtients image

Mycorrhizal fungi can multiply a plant's ability to extract phosphate by many hundreds of times.

Moreover, the excess phosphate drives the critical mycorrhizal fungi out of the rhizosphere, depriving that organism’s contribution of phosphatase enzyme, needed to extract complexed phosphate and trace elements out of the soil. Thus over-applying phosphate ironically leads to a deficiency of plant phosphorus, needed to produce ATP (adenosine triphosphate), the energy currency in the Krebs cycle for both plants and animals.

What does it all mean? Neal Kinsey, of Kinsey Agricultural Services (KAS), a true adherent to the Albrecht principles of soil fertility, advises all his clients, (which include countless consultants in over 70 countries around the world), to use Perry Agricultural Laboratories (PAL) for their soil tests. PAL uses the Bray II (root acid soluble) test for soils with pHs up to 7.5. Once the pH gets to 7.6 and above, they provide an Olsen P test result. Since there are at least 12 tests to choose from, why do NZ labs use the wrong one? The Americans use it appropriately and we in NZ have been led to believe it is a true measure of our soil P, when it is not.

On average, most of acid phosphates tie up or complex with aluminium, iron, manganese and calcium, within six weeks; sometimes within hours of application. But, super’s big marketing ploy is its low cost. How cheap is a material that is on average not very effective? Remember, chemical agriculture is a self-serving, input-driven system. You are advised to apply an unbalanced fertiliser to an unbalanced soil to help sustain a state of imbalance, which will then require constant chemical intervention. Now we have an inappropriate P test and an inappropriate product. When compared to alkaline phosphate products the answer comes out very much in favour of alkaline products such as guano, Sechura RPR, dicalcic and DAP. If needed, you can quickly build soil P levels with those products without those tying-up problems.

Sinclair** et al (1997) took the average curve and examined how good it was at explaining the relationship between % relative pasture yield and Olsen P values at 17 of the 19 sites. The result (Figure 4.1.16) (of the Massey University “Sustainable Nutrient Management in New Zealand” manual) is somewhat sobering! Sinclair et al (1997) concluded that Olsen P soil tests from farms could not accurately predict relative pasture yield. These data, however, did show that when Olsen P values exceed 20 a near maximum relative yield can be produced.

When we add the demise of mycorrhizal fungi (VAM) into the equation, the situation becomes even clearer. There is little or no reason to use superphosphate, as the VAM increases the effectiveness of phosphate uptake of roots by up to 1000 times. Loss of VAM leads to increased soil erosion and leaching of nutrients from the soil. When the VAM is lost, some other organism will take its place. Usually it is a pathogenic organism. Since properties I have worked with have no facial eczema, it seems a good bet that those using alternative phosphates will also not be bothered by that terrible affliction.

As for excess phosphate in the soil, on reviewing soil tests taken on flats, 90% had an excess, some being in the plus 700kg bracket. The hills were a different proposition as 86% were deficient.


1100 kg/ha

Hard Rock Phosphate

330 kg/ha

Triple Super
























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The difference between rock phosphate and acid phosphate (USA data)

Not only do we have criticism from USA regarding the use of the Olsen P test; we also have it from New Zealand. It appears the use of the Olsen P test was chosen in the 1970’s for no other reason than it being the latest test. It appears fertiliser companies have used the Olsen P test ever since for the purpose of selling superphosphate, a product that they manufacture; not because the farms actually need it.

In general, and depending on location, Kiwi Fertiliser finds P levels of NZ soils to be excessive. Where phosphate is required, we recommend Sechura RPR.

As for excess phosphate in the soil, on reviewing soil tests taken on flats, 90% had an excess, some being in the plus 700kg bracket. The hills were a different proposition as 86% were deficient.

* The late Jerry Brunetti was managing director of Agri-Dynamics, which specialises in products for farm livestock and pets, and consults on a wide variety of other issues. He used to be reached at Agri-Dynamics, P.O. Box 267, Martins Creek, Pennsylvania 18063, phone 877-393-4484, email, website

(**The late Dr A G Sinclair, AgResearch, Invermay Agricultural Centre.)

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