Independent trials show benefits of autumn-applied Polysulphate

An autumn application of ICL Polysulphate multi-nutrient fertiliser to supplement conventional spring timings can increase wheat yields by 0.3t/ha and significantly decrease leaching of N and P over the winter months, new trials are suggesting.

4 mins
Scott Garnett

Adding an Autumn application of ICL Polysulphate multi-nutrient fertiliser to supplement conventional spring timings can increase wheat yields by 0.3t/ha according to a three-year trial carried out by ICL and independent field trials specialists Envirofield.

At current prices, return on investment (ROI) would be in the region of 3:1 with better nitrogen utilisation efficiency (NUE) and increased root growth being the main reasons behind the yield gains seen, says ICL agronomist Scott Garnett.

“Previous trials in winter wheat have shown a 5 – 8% increase in yields from spring-applied Polysulphate by itself, but this latest work shows a further significant response from an initial application of the product in the Autumn.

“The trials, carried out in Suffolk on loam soil using the variety Skyfall, showed a single 100kg Polysulphate/ha application in the spring to provide around 50kg SO3/ha, delivered an average yield over the three years of 10.49t/ha.

“But when this was preceded by a supplementary application of 100kg of Polysulphate/ha the previous Autumn, an average yield of 10.79t/ha was achieved – an increase of 0.3t/ha.

“At current prices of around £200/tonne for both Polysulphate and wheat, this means the £20/ha cost of the additional Autumn application produced an extra income of £60/ha.”


Optimising NUE

Polysulphate’s prolonged release action and unique 48% SO3, 14% K2O, 6% MgO and 17% CaO analysis was key to achieving the results seen, he believes.

“Optimum levels of sulphur are essential in driving nitrogen utilisation but practically all soils in the UK are deficient in this vital element now, so no matter how much N you apply, without sulphur you will never get the most out of it.

“Polysulphate’s 48% SO3 content rapidly builds sulphur to the optimum level in the soil and the prolonged release nature of the product keeps levels topped up as plants develop through the Autumn.

“In fact, University of Nottingham trials have shown over 50% of the sulphur contained in Polysulphate is available in the first 12 days after application with the remainder released over the following 6 – 8 weeks.

“Potassium is also essential in maximising NUE, so the 17% K2O in Polysulphate plays a vital role alongside the high level of sulphur contained.”


Developing early root mass

Creation of early root mass is another yield-building benefit of Autumn-applied Polysulphate, Scott Garnett says.

“We have done a lot of work on how Polysulphate affects establishment of crops and there is clear evidence the calcium and magnesium it contains encourage greater phosphate uptake by the plants and significant development of roots.

“Trials in wheat show 34% greater phosphate uptake by plants receiving the Autumn application of Polysulphate and this is directly proportional to the extra root mass seen.

“This aligns with other trials across a range of crops showing a consistent 30 – 40% increase in phosphate uptake from Polysulphate.

“With an Autumn application crops are, therefore, able to build a strong root network ahead of the Winter and this helps with establishment and nutrient uptake as well encouraging better plant health and overall resilience.”


Environmental benefits

These trials have also shown the additional nitrogen uptake from Autumn-applied Polysulphate to be 36%, equivalent to 10kg N/ha more N been taken up by crops over the winter period, he points out.

“This combined with the increased phosphate uptake means the potential for loss of key nutrients from the soil over the Winter period is considerably reduced.

“So, not only are we getting vital extra nitrogen and phosphate into the crop, there are environmental benefits too, plus the extra root mass means the plants are much stronger and healthier overall and will get away quicker following the winter.

“This sets plants up perfectly to make full use of nitrogen in the spring and all adds up to the crop being able to produce the 0.3t/ha yield increase we have seen in the trials.

“Growers wishing to take full advantage of these benefits have two main options regarding applications this Autumn.

“Polysulphate can be applied from early October to before Christmas either broadcast using conventional fertiliser spreaders or direct-drilled with the seed.”


Sustainable future

Polysulphate has many other important benefits in modern sustainable crop production systems, he says.

“For a start it’s a naturally occurring fertiliser mined by ICL from under the North Sea requiring only minimal processing to make it an easy-to-apply product with excellent physical properties and performance right up to the widest spreading widths of 36.0m and more.

“Polysulphate can be applied by itself or blended with nitrogen fertiliser to provide the precise N:S ratio for an individual growing situation and to help farmers achieve ‘little and often’ applications.

“The fact that Polysulphate contains no nitrogen also allows producers to take full advantage of the most environmentally-friendly nitrogen sources such as the latest inhibited or control release fertiliser urea fertilisers and foliar products.

“In fact, Rothamsted Research estimates that by breaking the link between nitrogen and sulphur, use of Polysulphate alongside alternative low emission nitrogen fertilisers could decrease ammonia emissions from sulphur fertiliser applications by 90%.”

Polysulphate also has the lowest carbon footprint of all equivalent fertilisers at just 0.029 kg CO2e which is less than 6% of the carbon footprint of nitrogen sulphur products, Scott Garnett points out.

“At a time when the food industry is focused on the sustainability of its supply, these are significant considerations and ICL is already seeing interest from not just growers but also key multiple retailers keen to understand how they can reduce the carbon footprint of the products they sell.

“All in all, Polysulphate represent a new generation of fertilisers more closely aligned to the needs of growers, the wider food industry and consumers in the future.”