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  • Writer's picturePhilip

Marry Me!

"The handsome young gentleman dismounted his horse. He was courteous, well educated and wealthy the answer to a maiden's prayer, to be sure."

I often wondered where and how the Maiden's Prayer came to be! This week saw another answer to the Maidens Prayer, somewhat different to one of its original answers.

The question of buying Phosphate fertiliser arose.

"How little phosphate fertiliser can I get away with buying this year? The fertiliser Rep tells me I can reduce my purchase by using Slow Release Phosphate Fertiliser."

So what is on offer? Well most likely it is Struvite.

What is Struvite?

Struvite is a chemical compound that contains not only phosphorus, but magnesium and other elements like nitrogen. It is currently being touted as a slow release fertiliser that may be used in agriculture as an alternative to mined rock phosphate (in all its forms) and solve everything by simply reusing phosphorus from wastewater treatment plants.

How is Struvite recovered from wastewater?

Very simply put, by the process of precipitation. Often other chemicals are added to wastewater causing a reaction resulting in the formation of Struvite crystals. More recently, researchers have developed ways to use electrochemical precipitation. By applying an electrical current to a phosphorus and nitrogen containing solution, Struvite crystals form on a magnesium electrode. These either “precipitate out” or the magnesium electrode can be dried and the crystals scraped off for collection.

Both chemically and electrochemically precipitated Struvite are classed as a recycled fertiliser product.

Now the marketing text

Struvite behaves differently in various pH conditions dissolving very slowly under neutral to basic conditions (pH 7 or greater). Soil becomes somewhat acidified (pH less than 7) around plant roots.

Now this maybe correct but what the science states is

“Changes of rhizosphere pH depending on plant nutrition and plant species”


“It has been reported that the changes of the rhizosphere pH are restricted to a narrow zone around the root. Also it is difficult to measure the changes of pH experimentally within the 1 mm band in which this occurs.”

AND to top this off, depending on the starting pH of the soil this zone can either decrease OR INCREASE in its p.H…

As Struvite slowly dissolves near plant roots, the phosphorus, nitrogen, and magnesium become available for plant uptake when the plants need the nutrients.

As a result, Struvite has slow-release properties in soil when used as an agricultural phosphorus source. Struvite has been applied to fields either by surface application or by mixing into the soil.

When other commonly used, commercially available inorganic fertiliser sources are used, the phosphorus typically quickly binds to the soil. This makes the phosphorus unavailable for plant uptake. Because of Struvite’s slow-release behaviour, it may reduce the amount of phosphorus escaping into waterways and be helpful to the environment. Struvite’s slow release may benefit the environment.

Hang on! I thought we were buying fertiliser to improve crop yield and quality in 23/24 let alone improve our profit margins!


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