How to restore sulphur and key nutrient levels in soil this autumn

• Recent wet weather adding to diminishing soil sulphur levels
• Soils need urgent correction of many key nutrient levels
• Major yield and quality lifts resulting

With soil sulphur and other key nutrient levels at critically low levels following the recent exceptionally wet months, growers should consider using strategic applications this autumn to give winter crops a vital boost ahead of the spring, says ICL Growing Solutions agronomist Scott Garnett.

Ensuring adequate nutrition for establishment will be essential if crops are to deliver their full potential next year, with the effects of poor early root development and weaker plants being difficult to counter with spring applications alone, he explains.

“Every seed sown has a theoretical yield potential which can be reduced over the growing season by a host of factors including poor seedbeds, adverse weather, pest and disease, so giving crops the best start possible is key.

“Effective establishment is the foundation on which yield and quality of autumn-sown crops is built and adequate nutrition in this period is critical.

“If you look at sulphur, for example, a review of independent analyses by Lancrop Laboratories over recent years shows a growing number of soils are deficient in sulphur following the reduction in emissions from industry.

“The amount of sulphur from the atmosphere is around 2 percent of that occurring in the 1970s – totally inadequate for the nation’s farmland – with as much as 97% of UK soils now classed as ‘low’ or ‘critically low’ for sulphur deposits.

“The last year’s high levels of rainfall have made an already poor situation much worse and remedial action should now be a priority for growers.

“A good supply of key nutrients in autumn will not only encourage early formation of root mass and strong plant growth, it will also ensure plants grow away strongly in spring.”

Increased NUE

Three-years of trials carried out by ICL and independent field trials specialists Envirofield, have shown better nutrient utilisation efficiency and increased root development from autumn applications of multi-nutrient Polysulphate, he explains.

“Spring applications of Polysulphate have been shown to increase wheat yields by 5 – 8% but including an autumn application in addition, can increase wheat yields by a further 0.3t/ha and significantly reduce losses of N and P over the winter months.

“This results in a typical 30-40% increase in root mass with this larger root mass improving the plant’s ability to access more soil-bound nutrients and water leading to a stronger, healthier plant going into the winter.

“This is highly significant when you consider an extra centimetre of root on each plant will touch an extra 130 tonnes of soil per ha.

“In ICL winter wheat establishment trials in 2020/21, an application of 100 kg/ha of Polysulphate increased phosphate and nitrogen uptake by 41% and 28% respectively.

“Other trials have suggested the ROI from the yield gains resulting from autumn Polysulphate application is around £45/ha at current prices.”

Prolonged release

One of the biggest benefits of using Polysulphate (48% SO₃, 14% K₂O, 6% MgO and 17% CaO) in autumn is that it provides a prolonged release of plant soluble sulphur over 50 days in addition to essential potash, magnesium and calcium, Scott Garnett points out.

“As plants can only take up so much sulphur at a time, this prolonged release enables roots to take up nutrients as and when they need it.

“It also helps reduce potential losses of valuable nutrients into water and air, improving both the efficiency with which plants take these up and reducing possible environmental issues.”

“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.”

ICL recommends 100kg/ha of Polysulphate or ICL PKpluS or PotashpluS is applied in the autumn in addition to spring applications, he explains.

“Use of Polysulphate is both simple and flexible with a range of options to suit all farming systems.

“The product can be applied from early October to before Christmas either as a straight or in a blend as part of a grower’s autumn fertiliser programme. It can be broadcast using conventional fertiliser spreaders or direct-drilled with the seed.”

Benefits of autumn applications

• Sulphur applied in autumn improves retention of other nutrients and helps capture/retain soil nitrogen reserves. In oilseed rape, it will reduce senescence of lower leaves over winter.
• Phosphate deficiency leads to reduced movement of all nutrients around the plant resulting in poor establishment. More P can be removed at harvest than is applied so monitoring of indices is essential.
• Potassium is involved in every single process within the plant and essential alongside sulphur to maximise nutrient use efficiency.
• Calcium and magnesium are both critical for root development and seed establishment and essential in allowing plants to utilise residual and mineralised nitrogen in the soil.