How a single Polysulphate™ application feeds crops for longer

Read how multi-nutrient Polysulphate™ feeds crops for longer due to it's prolonged release pattern, which matches the uptake of the plant.

September 1, 2022
5 mins
Scott Garnett
England, UK

Polysulphate has many unique traits. First, it is derived from a naturally-occurring mineral called Polyhalite which is mined 1,200m below ground at ICL Boulby in North Yorkshire – the only mine in the world to extract it.

To create Polysulphate, polyhalite is simply crushed and screened, which is also done at the Boulby mine. As no industrial, or chemical processing, is needed to create the final product, Polysulphate is a fertiliser with an extremely low carbon footprint.

Polysulphate has a unique blend of crop nutrients – 48 per cent sulphur, 17 per cent calcium, 14 per cent potassium, and 6 per cent magnesium. It contains no nitrogen, enabling farmers to devise nutrient programmes that include nitrogen from bought in, or organic sources.

And its high specific gravity makes for a dense product that is easy to stack and store, saving room in your barn when you need it most.

But perhaps its most unique characteristic, and the one that really sets it apart from other fertilisers, is the way it releases nutrients into the soil. Polysulphate breaks down gradually releasing nutrients over a longer period that matches more closely a crop’s uptake.

What is prolonged release?

Prolonged release refers to how Polysulphate dissolves over time and slowly releases nutrients for crop uptake.

Because Polysulphate is a naturally occurring mineral, it takes longer to breakdown than other, manufactured fertilisers, meaning nutrients are available in the soil for longer.

In fact, Polysulphate continues providing nutrients to the soil over a 50 – 60 day period after application, in effect drip-feeding the crop as it grows to promote optimal nutrient uptake.

However, 60 per cent of the nutrients in the fertiliser are available in the first 12 days after application, providing the right concentration of nourishment at the right time.

Chris Dawson, independent agronomist at Chris Dawson Associates, said a benefit of Polysulphate is that its release of nutrients is more in line with the needs of the growing plant.

“Some nutrients are available straight away,” Chris said.

“The rest are released slowly over time as the plant grows and needs them, meaning they are available at the right times and in the right amounts to do the best job.”

This is in stark contrast to many other types of fertiliser, which may have released all their nutrients into the soil just days after being applied.

When this happens, plants are often unable to effectively utilise the sudden surge of nourishment, meaning a considerable proportion of the fertiliser may be wasted.

Not only does the prolonged release nature of Polysulphate avoid this, it also has another significant benefit, and one that has positive implications for a farmer’s pocket and the environment.

Financially, Polysulphate products aid nitrogen uptake, improve nutrient use efficiency and reduce loss of expensive inputs.

Reduced leaching

Leaching is a headache for everyone connected with farming. Not only does it mean expensive crop inputs are washed from the root zone where they are needed most, but they can end up in local watercourses where they adversely affect both the chemical make up and biology.

N and N+S products are particularly susceptible to this as nitrates are highly soluble in water and can be quickly washed away from the root zone, even after moderate rainfall. Sulphate ions are negatively charged, meaning they are repelled by soil particles which also tend to be negatively charged, and so are pushed through the soil profile quickly and out to the margins, where they do no good at all.

But the prolonged release mechanism of Polysulphate minimises the risk of leaching, as it supplies vital nutrients to the plant at a time when it needs it most and keeps the remaining nutrients where they ought to be – in the soil around crop roots. The breakdown of the mineral occurs at a rate that the plant can fully utilise, meaning there is no excess sulphur given up to be leached away.

This provides a multitude of benefits to the farmer and their crops.

Sulphur, as many will know, is essential for the optimal uptake of nitrogen which is needed to make plant proteins and ultimately deliver good plant health. So, not only does the prolonged release of sulphur from Polysulphate enable the crop to maximise the use of nitrogen throughout the growing cycle, by bringing efficiencies to this process, it may even reduce the amount of nitrogen needing to be applied to the crop, which increases returns for the farmer in the long run. It’s a win-win, and one that is easily delivered by introducing Polysulphate into a nutrient programme.

However, although this lack of leaching is highly beneficial, it is intrinsically linked to a question we often get asked, which is “Why is it I can still see Polysulphate granules in the crop weeks after I applied it?”

Still seeing Polysulphate™ weeks after application?

Many farmers – especially those who have applied Polysulphate for the first time – remark that they can still see the product lying on their fields long after application. This has even led some to conclude that it isn’t working.

Scott Garnett, ICL’s Head of Agronomy for the UK & Ireland, said seeing the granules shows Polysulphate is releasing its nutrients over a longer period of time, which is the key to its efficacy.

He said: “Polysulphate is a natural product that releases nutrients over 50 – 60 days, so it is not unusual to find chips of it still in the field after two or three weeks or even longer.

“Seeing this underlines the fact the product is working as it should, gradually feeding crops over an extended time period rather than applying all the nutrients at once, with the risk of them being leached away.

“So, if you are still seeing it weeks after application, it’s not a cause for concern. It is a sign that the product is doing what it is supposed to do.”

Scott added that due to the prolonged release, there was a belief that Polysulphate can only be applied early in the season – January or February – so that all its stored nutrients can be released.

However, ICL trials proved that later applications, in April or even May, can still deliver the same crop benefits from those made earlier in the year.

“Polysulphate is a particularly versatile fertiliser that will fit into most nutrients programmes,” Scott said.

“The prolonged release mechanism really works to ensure your crops are continually nourished and that they optimise nitrogen use efficiency, regardless of when you apply it.”