Exposing myths in a Post Truth Era

Fert Options
with Robin Boom
Agronomic Advisory Services

We live in a post-truth world where opinion is given as much credence as fact, where social media is swamped with legitimate looking fake news. Where mainstream media only gives oxygen to particular social and political agendas, and where paid advertising can manipulate the truth for the betterment of the product seller.

Through this column I’ve waxed on about some of the dishonesty and lack of debate on the issue of climate change. And for anyone interested I have a four-minute YouTube clip countering the alarmist metanarrative which can be seen here: https://www.youtube.com/watch?v=BiMYmRpmm9A

When it comes to claims on various fertilisers and soil fertility issues, I’ve heard a number of ‘myths’ that farmers have been told over the years, or ideas they have embraced which are plainly incorrect. Mark Twain once stated ‘There are lies, damned lies and statistics’, and unfortunately data can be manipulated or twisted to legitimise a particular fallacy which is then regarded as a scientific fact.

Here are some myths I’ve come across.

Myth 1:

That 250kg of granulated fine particle lime is the equivalent of 2.5 tonne of standard lime.

This is totally incorrect. The fine particle lime may work quicker in displacing hydrogen ions and lift the pH quicker than coarser lime material, but once it is ‘spent’ its effect has gone, whereas the coarser lime will keep dissolving over a number of years and keep working. Fine particle granulated lime typically costs ten times as much per tonne and these sorts of claims are made by manufacturers to legitimise the sales of their expensive lime products. There may be some ballistic advantages with granulated limes, particularly when being flown on, but even if half of a standard lime blows away, which it doesn’t, at 10 times the cost, it is an expensive way of raising soil pH.

Myth 2:

That 20 litres/ha of liquid seaweed is an effective fertiliser.

Seaweed has very little natural nutrient value, except for a small amount of potassium. Liquid products are often fortified with artificial NPK and trace mineral additives, but even these applied at such light rates have limited value when mixed with water and sprayed on. To get the right amount of nutrient to maintain pasture or crop production, the fortified seaweed would have to be applied at such high rates, that it would be completely uneconomic. Seaweed may have some sort of ‘tonic’ value, as it contains certain plant hormones and has been shown to reduce the effects ryegrass staggers and other fungal toxins affecting livestock, but as a fertiliser itself seaweed is a very expensive source of nutrients.

Myth 3:

The Olsen P test was designed for New Zealand soils.

The Olsen P test was developed by Dr Olsen in Colorado in the early-1950s for the alkaline soils of the mid-west of America. Here in New Zealand it was compared against the Truog and Bray 1 tests in the 1970s and was found to be a more reliable test for predicting phosphorus responses than the standard Truog test used back then. Many trials were conducted around the country on different soils calibrating pasture production to Olsen P figures in the 1970s and 1980s. More modern soil tests such as the Resin P and Mehlich III have been shown to more accurately predict phosphate responses on acidic soils. But the Government is unlikely to ever throw many millions of dollars into calibrating crop and pasture responses to these newer tests. The Olsen P is still regarded internationally as a good test on alkaline soils. In the UK for instance, the Olsen P test is the main test used on the alkaline calcareous soils of England, whereas for the acidic soils in Scotland, the Morgan test is the preferred option.

Myth 4:

All RPR fertilisers work similarly and are effective sources of phosphate.

To be classified as a Reactive Phosphate Rock, at least 30 per cent of the total phosphate content must dissolve in a citric acid solution. Generally, the higher the percentage of phosphate that dissolves, the quicker it will become available for plants to utilise. Alternative tests such as formic acid have been shown to more accurately mimic phosphate dissolution of RPR fertilisers, but overall trends generally are similar. Field trials have shown significant differences in the performance of different RPR fertilisers, with higher soluble products like Sechura working a lot faster than some Mediterranean rocks, which can take decades to fully work.

Myth 5:

The chloride in Muriate of Potash is harmful to the soil.

High amounts of chlorine will sterilise soil media, but chloride and chlorine are different animals. Plants actually need small amounts of chloride, and pasture dry matter is typically around one per cent chloride, with more chloride taken up than phosphorus. Many critics of muriate of potash (potassium chloride) are advocates of sea salt, which has a higher percentage of chloride, and the most common element in the sea apart from hydrogen and oxygen is chloride. Yet the sea is teaming with micro-organisms in an environment many times richer in chloride than what we get when applying potassium chloride as a fertiliser source.

In my next column I will elaborate on more ‘myths’ of the fertiliser industry.

Robin Boom, CPAg, member of the Institute of Professional Soil Scientists. Ph: 0274448764.


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