Reducing nitrogen fertiliser use

Article by Rosalind Platt, managing director of BFS Fertiliser Services, UK leaders in crop nutrition since 1948, published in Direct Driller magazine.

Late-season foliar nitrogen applications can significantly lower the total nitrogen required in crop production while maintaining – or even increasing – yields. Recent research has shown particularly strong results in oats.

Ongoing volatility in the fertiliser market continues to place pressure on farmers. At the same time, the industry's shift toward Net Zero has encouraged the development of more efficient nutrient strategies. In response, BFS developed a foliar nitrogen product, PolyNPlus.

Following five years of independent trials carried out by organisations such as Niab and Velcourt, along with tramline trials conducted by a number of growers and agronomists, PolyNPlus has consistently delivered positive results. More recent studies on spring oats – now increasingly used as a break crop ahead of winter wheat – have also shown encouraging outcomes.

Traditionally, farmers apply soil-based nitrogen fertilisers two or three times during spring. However, nitrogen use efficiency (NUE) from soil applications can fall to around 25% later in the season, particularly in dry conditions.

Long-term research shows that PolyNPlus foliar nitrogen can reduce overall nitrogen requirements without compromising yields. Once sufficient leaf canopy has developed, it can partially replace soil-applied nitrogen. For example, applying 25 litres of PolyNPlus (equivalent to just 8kg of nitrogen) between growth stages 32 and 39 can replace 40–50kg of conventional soil-applied nitrogen. Alternatively, some growers apply two treatments of 15 litres per hectare at growth stages 32 and 37.

PolyNPlus is safe for application to growing crops and can be tank-mixed with fungicides, reducing the need for additional field passes. This improves efficiency while lowering input use.

Trial results support these benefits. A Velcourt study on Crusoe winter wheat in Lincolnshire found that lower nitrogen inputs combined with PolyNPlus produced comparable or improved yields – see chart. Additionally, replacing 40kg of soil-applied nitrogen with 25 litres of PolyNPlus reduced the carbon footprint of the third application by 77%.

As well as wheat and oilseed rape, PolyNPlus can also be used in oats, applied just before panicle emergence. While oats require adequate nitrogen for optimal yields, excessive nitrogen can increase the risk of lodging. Although plant growth regulators can reduce this risk, they may also negatively affect grain quality.

A recent trial in Wiltshire investigated whether foliar nitrogen could improve efficiency. The crop received a standard 90kg/ha of soil-applied nitrogen alongside fungicide, without a growth regulator. A PolyNPlus product, PolyNPro, was applied at different stages: flag leaf (GS39), heading (GS59), both stages combined, and compared with an untreated control. The findings were promising. Dual applications at GS39 and GS59 resulted in a significantly higher specific weight – see chart.

Further data from ongoing oat trials will be available after this season's harvest.

How PolyNPlus works

Soil-applied urea undergoes multiple biological transformations before becoming available to the plant. These processes consume energy and reduce the amount of nitrogen ultimately absorbed by the plant.

In contrast, PolyNPlus is absorbed directly through the leaf, leading to much higher NUE. Its formulation includes molecules of varying chain lengths: shorter chains are absorbed rapidly, while longer chains release nitrogen gradually over time. This sustained delivery allows the plant to utilise nitrogen more effectively.

Six different formulations

The PolyNPlus product range is formulated with ureic polymers, sulphur, magnesium, manganese, micro-nutrients and organic uptake enhancers. Uniquely, there are six formulations to meet different crop needs: PolyNPlus Cereals, PolyNPlus ManMag, PolyNPlus High Sulphur, Straight PolyN. Also available with required trace elements for oilseed rape and maize are: PolyNPlus Oilseed and PolyNPlus Maize. 

A more efficient future

Foliar nitrogen is expected to play a key role in the future of sustainable farming. It offers a practical and cost-effective approach to improving nitrogen efficiency, maintaining or boosting yields, reducing environmental impact and lowering farm carbon emissions.