A bumper year for grassland production has filled silage clamps across Scotland, but livestock farmers must consider the likely toll on soil nutrient resources and start planning now to ensure sustainable high yields in the future.

With many Scottish livestock producers producing significantly more forage than during the challenging year of 2018, removal of key nutrients from soil resources will be considerable this year, warns fertiliser specialist Jim McMullan of Galloway & Macleod.

Nitrogen levels are likely to have been depleted in recent months but so too will have Phosphorus, Potassium and Sulphur with appropriate fertiliser management strategies now needed to ensure levels are restored effectively, he believes.

“It’s been a great year for grassland production generally which is great news for dairy and livestock producers, especially after last year when many struggled to make enough silage to see them through the winter.

“But this will have affected soil nutrient levels, so the challenge now is to make sure 2019 does not become a one-off for grassland production and this will involve care with nutrition strategy with soil testing being key.

“In intensive grassland systems you really have to test each field for P, K, Mg and pH at least every 3 years but there is a strong case for testing more this year, particularly on fields that were borderline on the targets of pH 6.5, and medium for P and K respectively.”

Potassium (K) for example, is one of the main driving forces of grass yield and the element most removed in good years, he says.

“The primary role of K is to ensure efficient movement of nutrients within the plant but it also helps maintain plant cell strength, critical in supporting the high growth achieved when Nitrogen is applied, and it also helps plants cope with stress.

“FYM contains valuable levels of P and K and can have a positive impact on grassland nutrient management but there are big variations in nutrient composition in different sources so you must carry out tests pre-application and account for this before applying additional nutrients.”

Sulphur is also likely to have been removed from the system in a significant quantity this year with AN-based true granular compounds containing Sulphur being the preferred choice for addressing this, Jim McMullan points out.

“In our own trials with silage at Gartclush in Stirlingshire such compounds a produced an extra 20% dry matter yield over a urea plus Sulphur blend, which was worth £360/ha in terms of milk production.

“In grazing, the advantage of using AN plus Sulphur over straight AN rose as high as 65%.”

“Sulphur is a major component of the protein-forming amino acids and is essential when higher amounts of Nitrogen are applied. Levels have to be kept proportional to the amount of Nitrogen used and the best way to determine these is to assess levels in the growing grass.

“As well as atmospheric levels being much lower than they used to be, Sulphur is routinely lost from the soil system and so regular applications have to be made throughout the season to keep levels adequate for optimum Nitrogen utilisation and crude protein production.

“Whilst slurry is a good source of P and K, there is little Sulphur in cattle slurry and the vast majority is not available for plant growth.”

According to Mark Garrett of CF Fertilisers, the simplest way to effectively address the nutrient shortfall, keep all essential elements in balance and ensure they are delivered in the best way possible to growing swards is to use NKS and NPKS compounds.

“Such compounds, alongside slurries and manures, are the ideal way to restore nutrient levels in high productions systems or in years when take-off of grass has been substantial.

“As well as making sure nutrients are delivered accurately due to their compound nature, British-made true granular products are also based on Ammonium Nitrate (AN) which has been proven over many years to be the most effective source of N for grassland production systems.”

In trials over the three years 2015 to 2017, the higher performance of AN over urea resulted in an average yield gain of 15% over first and second cut with a wide variation in results achieved from all the urea-treated land, he points out.

“When an AN-based true granular Sulphur compound is used, the results become even more impressive.

“Over three years of trials between 2016 and 2018, we saw an average 20% improvement in grazed grass yields from using SingleTop (27N + 12 SO3) over AN and in silage this was around 23%”

NKS and NPKS true granular compounds build on the foundation of NS compounds like SingleTop to provide a balanced supply of P and K, Mark Garret explains.

“NKS products are particularly beneficial where P index is high, slurry is used on aftermaths and soil Potash levels need to be maintained.

“MultiCut Sulphur (23-4-13 + 7SO3) can be used as an all season high Nitrogen/high Potash product ideal for multiple cuts of grass silage with reduced Phosphate content to help maintain soil P and K status.

“If the soil P index is high but the K index low, particularly if it’s on a lighter soil type, producers should consider using SingleTop (27N + 12SO3) in spring then KayNitro Sulphur (25-0-13 +7SO3) in the summer.”

It’s always worth investing in such fertiliser strategies, Mark Garrett says.

“Grass energy is cheaper than concentrate feed energy regardless of the system so no matter how you farm, improving Nitrogen fertiliser use efficiency (NfUE) from better fertilisers and management will always improve profitability.

“Our calculations show that in terms of return on investment (ROI) for every £1 you spend on Nitram (34.5%N) you can expect to see a £7 return across the business – if you’re on an all-silage system this will rise to a £9 return for every £1 spent.

“When you start managing other nutrients such as P, K and S effectively, the AN advantage grows.”