To the Editor of the Australian Nutgrower,
Over the past number of years, the number of advertisements for new, novel or alternative fertiliser products making astonishing and enticing claims has grown significantly. The claims made by the manufacturers about their products and what they can do for production, soil improvement, plant health and nutrition and crop quality are usually “miraculous”.
In most advertisements the claims read as statements of facts, which if reproducible in the field, will ensure my next hazelnut crop will be a bumper.
I wondered how these companies substantiate their claims. Surely, they must have significant data from replicated trials, and they may, but there is generally no reference to quality replicated data.
In a recent advertisement a manufacturer makes a claim their product contains over 60 minerals, yet there are only 17 scientifically proven and agreed nutrients essential for plant growth. The soil and the amendments we apply usually provide others in abundant amounts.
Reference is made to the product being citrate soluble (slow release). Is this all the elements or just one? Typically, citrate solubility is quoted when rock phosphate or products containing rock phosphate are involved.
Assuming then the product is predominantly rock phosphate as growers we need to understand the limitations with this form of phosphorus.
What is the percentage of citrate solubility? Low citrate solubility 10-15% means very little P may be released; 25-30% citrate solubility indicates considerably more P may be plant available.
We need to know where and how to use the product most effectively. Will it perform the same way at various soil pH and conditions? Is it effective in high and low rainfall environments or is irrigation required?
The advertisement claimed the product would increase soil pH at the same time as providing nutrients. The suggestion the product can raise soil pH leads me to believe the product is blended with calcium carbonate (lime) or possibly calcium sulphate (gypsum). If this is the case application rates will need to be extremely high to increase soil pH.
As a grower, who has been involved in the plant nutrition industry for more than 15 years, I have developed a very healthy level of scepticism of claims made about crop and soil nutrition products. The product may be very good and do all it claims but it provides no scientific facts or data to support the claims. This is the reason for penning this letter.
Plant and soil nutrition has been, and continues to be, very well researched but its application is not an exact science. As yet I have not come across anyone who one can say exactly how much of a nutrient to apply to your crop to correct a deficiency identified with a tissue or sap test.
I strongly doubt there is anyone who can recommend exactly how much nutrient to apply to increase plant levels to a specific target. Or when a nutrient is applied to the soil exactly how much will be plant available and taken up in a given year. Because of this and other factors some manufacturers get away with making erroneous or unsubstantiated claims about their products. This is particularly the case for trace element products as well as products which claim organic or biological status.
Lack of either strong legislation or the will to enforce current legislation supports an environment in which outlandish claims go unchallenged.
I encourage all growers and advisers to become better at challenging claims made about plant and soil nutrition inputs. Seek out good science, quality education (not only information) and knowledge. Understand the difference between soil and plant nutrition and comprehend the roles each plays in the management of a crop year to year and the soil long term.