Manage your grassland nutrition in a sustainable manner

Focusing on naturally occurring sulphur sources could play a major role in helping Scottish dairy and livestock producers optimise nitrogen utilisation in grassland and achieve significant productivity, carbon and environmental gains.

February 6, 2024
5 mins

Livestock and dairy farmers looking to produce forage in a more sustainable manner need to manage their use of nitrogen more efficiently, look more at N-fixing leguminous species in leys and use organic sources more effectively, says Allison Arden of nutrient planning specialists Navigate Eco Solutions.

“The aim is to optimise nitrogen applications from all sources, better target nutrient inputs to match grass demand and ensure farmers get as much production out of every kg applied as possible.

“A wider awareness of best practice for nutrient use in grassland and understanding the roles of nitrogen fixing legumes in leys, testing of FYM and slurry before applications plus working from a comprehensive nutrient plan, are key.

“Making sure as much of the available N in the soil as possible finds its way into plants thereby reducing the risk of excesses in the soil becoming vulnerable to leaching or ammonia loss to the air is also essential.”



Improving NUE key

Improving nitrogen utilisation efficiency (NUE) is one of the biggest challenges facing dairy and livestock producers currently with it having significant effects on the bottom line of production as well as the marketability of milk as buyers look to reduce the carbon footprint of their products, she says.

“We have to look at the most appropriate ways of increasing NUE and whilst this is not always easy in livestock systems, one of the key factors often overlooked by producers, is the role of sulphur in the NUE equation.

“Levels of atmospheric sulphur have been falling rapidly since the industrial clean-up some years ago, yet it plays an essential role in the ability of many crops, grass included, to recover and utilise nitrogen efficiently.

“Numerous trials have consistently shown 20% lifts in forage yields when appropriate levels of sulphur are used to drive NUE with a corresponding increase in grass quality, too.

“Sulphur is also essential in the production of specific amino acids and if absent, plants can’t use nitrogen as effectively and manufacture all the necessary protein efficiently.

“At a time when crude proteins in forage have been falling and the cost of bought-in protein supplements have been rising, this is something few milk producers can afford to ignore.

“It is also true that nitrogen fixing plants such as clover and other legumes are disadvantaged if sulphur supply is reduced.

“It is a necessary element for nitrogen fixation and, if in short supply, deficiency symptoms can quickly develop as the grasses starve the legumes of any availability.”

Scott Garnett, head of agronomy for crop nutrition specialist ICL agrees, saying environmentally-friendly sources of sulphur will have an increasingly important role to play in the future.

“It’s important that nutrients are managed effectively with a particular focus on optimising the use of nitrogen, so one of the most effective ways to achieve this is to use sulphur to improve NUE of all the nitrogen resources you have available.

“These could be from applied nitrogen, nitrogen fixed by legumes or that contained within FYM and slurries.”


Decoupling sulphur and nitrogen

Historically nitrogen and sulphur have been applied together in the form of nitrogen sulphur (NS) products, the trouble with these are they are sold in fixed ratios that do not often address the needs of the crop, he points out.

“Decoupling nitrogen from sulphur could, therefore, be a good start in being able to make more use of this vital element.

“With this in mind, there are some compelling reasons why the naturally occurring mineral Polysulphate, mined from under the North Sea, could be better source of sulphur for grassland than the traditional AS-based fertilisers in the future.

“For a start, it contains no nitrogen at all with a composition of 48% SO3, 14% K2O, 17% CaO and 6% MgO.

“This high concentration of sulphur makes it ideal for maximising the nitrogen produced from the growing use of legumes in grass mixes encouraged by SFI and reducing the overall dependency on inorganic fertilisers.

“Furthermore, Rothamsted Research has estimated the separation of nitrogen and sulphur could decrease ammonia emissions from sulphur fertiliser applications by 90%.

“This is the result of growers being able to choose low emission nitrogen fertilisers to apply alongside the polyhalite mineral rather than relying solely on traditional combined nitrogen sulphur products.

“Another key advantage is its prolonged release characteristics that deliver the sulphur and other nutrients over a period of 8 – 10 weeks, so these are constantly available to drive NUE throughout the growing season.”


Higher yields of better quality forage

It also means nitrogen and other key nutrients are utilised more fully so they are not left in the soil for long periods where they are vulnerable to leaching, he explains.

“This is also in contrast to standard fertiliser practice, where large amounts of available sulphur are usually applied to crops when they are not really in a position to utilise them fully.

“Extensive trials have, in fact, shown this sustained nutrient supply and ability to improve NUE can deliver an increase in grass yields of 29% together with an increase in drymatter of over 10%.

“The additional sulphur provided also significantly improved the protein content of the grass.

“All in all these improvements lead to denser, heavier, more nutrient-rich forage which, combined with the increased palatability and digestibility from a lift in sugars of over 9%, produces healthier, more productive cows for the same, or potentially less, cost.”

“As a natural mineral requiring only minimal processing, Polysulphate also has the lowest carbon footprint of any fertiliser on the market and is approved for use in organic grassland systems too.”

Peter Scott, technical director of Origin fertilisers, says their own work on the mineralhas highlighted particular improvements in the all-important crude protein of forage.

“We’ve seen positive trends in terms of forage yield, but it’s in the area of nutritional value and mineral content where we have seen the biggest gains.

“In one particular trial we saw a significantly improved N:S ration in forage which resulted in a 56.3% lift in the amount of sulphur contained in the forage and a corresponding crude protein increase of nearly 7.5%.

“We’ve found Polysulphate offers a very different release profile than other commonly used forms of sulphur and one that better matches the growth of the crop, which is one of the main reasons we are seeing such significant benefits in grassland.”