Autumn polysulphate boosts yield extra uptake of important nutrients for wheat crops

A multi-nutrient fertiliser to help supplement conventional spring applications can boost wheat yields and reduce leaching, according to new trials.

An autumn application of ICL polysulphate can increase yields by 0.3t/ha and significantly decrease leaching of nitrogen and phosphate over the winter months, suggests the three-year trial carried out in conjunction with independent field trials specialists Envirofield.

The results show better nutrient utilisation efficiency and increased root development, 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.

Carried out in Suffolk on loam soil with winter wheat Skyfall, the trials yielded an average of 10.49t/ha over the three years from a single 100kg polysulphate/ha application in the spring to provide around 50kg SO3/ha.

When this was preceded by a supplementary polysulphate application of 100k/ha, the previous autumn, an average yield of 10.79t/ha was achieved – an increase of 0.3t/ha.

“At current values, the cost of the extra application of polysulphate would be more than covered by the additional grain income plus there are significant environmental benefits to factor in too.”

More efficient

Polysulphate’s prolonged release action which comprises 48% sulphur, 14% potash, 6% magnesium and 17% calcium s, 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 nitrogen you apply, without sulphur you will never get the most out of it.

“Polysulphate’s 48% sulphur 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, Nottingham university 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 nitrogen use efficiency and the potassium in polysulphate plays a vital role alongside the high level of sulphur contained.”

Early root mass

Creation of early root mass is another yield-building benefit of autumn-applied polysulphate, says Mr Garnett.

“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 winter cereal crops 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.”

These trials have also shown the additional nitrogen uptake from autumn-applied polysulphate to be 36%, equivalent to 10kg N/ha more nitrogen 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.

“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.”

Options

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

“Polysulphate can be applied up to before Christmas either as a straight or in a blend as part of a grower’s autumn fertiliser programme,” says Mr Garnett. “It can be broadcast using conventional fertiliser spreaders or direct-drilled with the seed.”

It is also 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 36m and more.”