Improving the understanding of slurry nutrient content can significantly improve fertiliser efficiency and reduce environmental losses. At a UK Dairy Carbon Network (UK-DCN) workshop on 26 February 2026, farmers explored how assessing, timing and application methods can help unlock more value from slurry.
James Bretherton, soil specialist and director of Agscope Ltd., who led the workshop, outlined how effective slurry management can help improve nitrogen use efficiency while reducing emissions on dairy farms.
“Farmers manage nutrients all the time’’, said James. “From the feed, fertilisers and manures to the crops grown and the meat and milk produced – nutrients are constantly cycling through the system.”
Slurry composition often reflects the herd’s diet. For example, total mixed ration (TMR) systems typically produce more nutrient-dense slurry than low-input, grazed systems.
Understanding slurry value
Slurry represents a key component of the on-farm nutrient cycle and carries significant fertiliser value. Using a recent analysis of a 7% dry matter slurry, James demonstrated the potential plant-available nutrient content per 1,000 gallons: 11.5 units of nitrogen, 5 units of phosphate, 23 units of potassium, and 7 units of sulphur.
Based on recent fertiliser prices, James said this equates to around £4.36 of nitrogen, £1.17 of phosphorus and £7.20 of potassium.
“In total, that’s around £18 per 1,000 gallons – including magnesium and sulphur,” he explained.
Fertiliser market volatility also has an impact on slurry value. Following Russia’s invasion of Ukraine in 2022, for example, slurry value rose to around £30 per 1,000 gallons.
Measure to manage
“You can’t manage it if you don’t measure it,” James emphasised. “It costs about £70–80 to have slurry analysed, making it inexpensive relative to its fertiliser value and the potential improvements to nutrient planning.”
Farmers are advised to have their slurry evaluated initially to understand its nutrient profile, then reassessed whenever farm systems change, such as through diet adjustments or increased water entering storage.
James also highlighted the importance of accurate sulphur evaluation. “It is often stated that 70–80% of the country is deficient in sulphur, but that isn’t always the case. There is a risk of oversupply and damage to the diet – like locking up copper.”
Where slurry analysis is not achievable, James advised that standard values in AHDB’s Nutrient Management Guide (RB209) can provide a starting point, although analysis will always generate more accurate, farm-specific results.
Minimising nutrient losses
Nutrient losses from slurry primarily involve nitrogen and phosphate, occurring through various mechanisms and conditions.
Most nitrogen losses from slurry result from ammonia volatilisation – when ammonium converts to ammonia gas and escapes into the atmosphere. Losses during storage and at spreading can be significant: an open lagoon can lose around 2kg nitrogen/m² annually, while splash plate applications can lose up to 80% of total ammonia nitrogen (TAN).
Nitrogen can also be lost through nitrate leaching when crop demand is low and nitrates are in surplus.
“If the crop isn’t actively growing, the nutrient has nowhere to go. The plant can’t capture it, so you will lose it to water or to the atmosphere,” James explained.
Phosphate losses usually occur when slurry remains on the soil surface and rainfall causes runoff. Once incorporated into soil, phosphate becomes relatively immobile, although excessively high soil levels can impair zinc and selenium uptake in forage.
Timing and application
Applying slurry when crops can utilise the nutrients is key to minimising losses.
“Spread it when the crop needs it,” James advised. “If you are spreading in winter when grass is not growing, you are wasting those nutrients and increasing pollution risk.”
Adequate slurry storage capacity is crucial.
“If you are spreading it because there is inadequate slurry storage on the farm, then that should be a part of your investment discussions. When you have adequate storage, you grow more grass, because you can store it until the crop needs it.”
Most active grass growth occurs between the spring and autumn equinoxes (21 March to 21 September), when daylight exceeds 10 hours and soil temperatures reach at least 6°C, allowing soil biology to break down nutrients to their plant-available form.
James also stressed the importance of correcting soil pH and recommended applying lime in the final quarter of the year.
How slurries are spread is massively influential.
“Low-emission spreading systems like dribble bars or trailing shoes or even low-level spreader plates over splash plates, can help apply slurry closer to the soil surface,” advised James. “This improves nitrogen capture by crops and reduces environmental damage and nutrient losses.”
Application rates must also be managed carefully.
“A typical rate might be about 2,250 gallons per acre (5,560 gallons per hectare). But 4,500 gallons per acre (11,120 gallons per hectare) is high and 9,000 gallons per acre (22,239 gallons per hectare) is bad for soil, bad for worms and bad for the environment.”
Across the UK-DCN project, farms have adopted 33 nutrient management actions, making this one of the most widely implemented areas. The strong uptake highlights how these changes integrate seamlessly into everyday farm decisions, providing a practical way to boost efficiency, cut emissions and deliver immediate value.