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Less is more with prescription fertiliser (May 24)

Reducing total nitrogen inputs on grassland, by as much as 15%, without impacting returns is possible. And producers can reduce emissions and improve sustainability.


Producers looking to reduce emissions and improve sustainability will be aware that nitrogen fertiliser is a significant factor but will be wary of reducing its use if yield and forage quality are to be maintained.

Of all the nutrients, nitrogen is still the key driver for grass yield and protein content, so when fertiliser costs increased in 2022, many producers reduced applications of other primary, secondary and micronutrients in favour of nitrogen.

They may have navigated a single-year break of these nutrients without too much damage, but prolonged gaps for several years could allow nutrient deficiencies to appear in the soil profile. One option is to scale back on the total amount of nitrogen applied and use the saving for added nutrients, although many may view this as a risky strategy given nitrogen’s importance.

But Origin Fertilisers’ Tom Wells says trialling reduced nitrogen applications offered some interesting results and invaluable information. The work, carried out in 2023, set out to examine two fertiliser products side by side, on the same grassland crop, to assess the impact of lower nitrogen rates and prescription nutrition.

“It may seem odd that a fertiliser company would want to carry out a trial advocating using less nitrogen,” he says. “But if we can reduce application rates and still achieve similar results, or even increase the value of the end product, the fertiliser applied is more efficient.

The trial compared a standard calcium ammonium nitrate (CAN) application to a prescription fertiliser, called Sweetgrass, which includes sulphur and sodium.

The aim was to assess if the prescription fertiliser could offset a 15% reduction in mineral nitrogen and still offer comparable returns, with outcomes measured in dry matter yield and forage quality.

Fertiliser application: lowering nitrogen can reduce emissions and improve

business sustainability

Increased uptake

The total nitrogen (N) applied on the CAN area was 304kg/ha, whereas on the Sweetgrass area the total N was 259kg/ha – 14.8% less. The CAN product contained nitrogen only, and Sweetgrass comprised 23kg of N plus 5kg of sulphur (SO3) plus 5kg of sodium (Na2 O). The on-farm trial represented typical growing conditions experienced in 2023.

One of the most interesting outcomes of the work was that the forage on the prescription area showed an increased nitrogen uptake during analysis, despite having less applied.

“Grass was able to ‘access’ more of the nitrogen more efficiently, which reduced the amount of nitrogen that wasn’t used,” says Mr Wells.

“The term ‘nitrogen-use efficiency’ is a popular one, but this is a clear example of where the crop has benefited from the inclusion of other nutrients to access a greater percentage of the applied nitrogen. It also reinforces that grass requires other nutrients apart from nitrogen.”

A significant factor contributing to the increased uptake of nitrogen on the prescription area is the provision of other nutrients at plant-available levels because nutrients, such as sulphur, assist nitrogen uptake. The Sweetgrass fertiliser provided balanced nutrition for the grass to maximise returns, and there are notable benefits of applying this compared to a higher total product nitrogen.

Grass from the prescription area analysed at 15.2% dry matter (DM), while the CAN area was lower at 13.7%. This dry-matter yield benefit of 0.984t/ha, an increase of 13.3%, represents a sizable saving through growing higher-quality grass.

The additional DM could be worth as much as £177/ ha, based on a DM value for bought-in concentrate at £180/t, and analyses results revealed that it’s not just additional yield that producers could benefit from.

Cheapest feed

“Grass is the cheapest feed available to dairy herds, but only if the quality is sufficient to provide cows with as much nutrition as possible,” says Mr Wells. “The trial showed increases in crude protein, digestibility and energy, which are all key drivers for improving cow health and productivity. And this has been achieved by using less total nitrogen.”

A proportion of the increase in these key metrics will be down to the grass being more digestible due to the addition of sodium. Sodium improves the palatability of grass, improving intakes and making it easier to digest. Increasing intakes means grazed grass is supporting more milk production.

The refined sodium salt in Sweetgrass differs from a traditional agricultural salt. “It contains a coating that reduces the risk of it picking up moisture, even when blended with a wide range of other nutrients,” says Mr Wells. “It is also ‘size matched’ with nitrogen, phosphorus, potassium and sulphur raw materials, to reduce the risk of segregation, and deliver an even distribution of granules on application.”

As well as improved grass yields, the same trial saw crude protein increase by 1.8% to 21.1%, grass digestibility improve by 1.9% to 74.1%, and ME also increase from 10.7% to 10.9%. However, the wider sustainability benefits and reduction in greenhouse-gas (GHG) emissions should also be considered by producers when deciding on soil and grass nutrition.

Reduce emissions

“From a sustainability perspective, using less nitrogen will typically reduce GHG emissions, and we are lowering the risk of leaching nutrients into the environment by not applying excess nitrogen that isn’t taken up by the crop. This approach also has financial benefits as nitrogen is often a costly nutrient, so using less product more efficiently will help to support the bottom line,” adds Mr Wells.

Sweetgrass fertiliser reduced GHG emissions by 14.8% compared with CAN, which shows that by using the ‘correct’ fertiliser and providing the crop with the nutrition it requires, it is possible to contribute to reducing emissions through prescription-fertiliser use.

“Producers can reduce emissions through more targeted fertiliser use and still achieve the same, or better, returns on their investment.”

What is prescription nutrition?

Targeting soil nutrient deficiencies by using tailored fertiliser offers producers the chance to maintain and improve yields through maximising the investment in nutrition products. Using detailed soil analysis, Origin can match up to 15 different nutrients in a single product to correct any soil deficiencies. Using prescription nutrition achieves good results.

Data shows that it can reduce nitrogen use and achieve more, but having the correct nutrition in place to support grass growth is vital. Reducing nitrogen on its own can impact yield, but providing the soil with a wider range of nutrients ensures that grass leys have what they need to maintain performance.

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