A new approach to the use of “bugs” to improve the nutrient content of stored slurry has more than doubled the value of nitrogen on a dairy unit in Lancashire where the slurry nitrogen will be worth more than £30,000 over a 200-day winter.

This follows an analysis of slurry taken one month after the inoculant had been trickled into the lagoon from an automatic dispenser on the 340-cow dairy unit at the University of Lancashire’s Myerscough College, Preston. The 1.5m litres of treated slurry showed a cash increase in its nitrogen value of almost £5000 after four weeks.

The inoculant, SlurryBugs + SlurryBooster, has been developed by the Lancashire company EnviroSystems Greenlands, run by Liz Russell.

“This is a new inoculation system where the naturally occurring bacteria of the product SlurryBugs – used to break down the organic material in slurry and preserve its N, P and K content – is combined with the nutrient SlurryBooster to increase the bacterial activity.

“We believe the combination of the two systems is a major breakthrough in increasing the manurial value of slurry to farmers who are facing rocketing fertiliser costs. Although these results are from a single trial, they are consistent with our laboratory results,” says Ms Russell.

Slurry spreading

The inoculant – which also creates a more consistently liquid slurry and reduces odour – achieved a significant increase in the nitrogen content of the slurry compared with untreated material on the Lancashire farm.

Slurry analysed after one month’s treatment showed it contained 41mg/litre of N compared with 14mg/litre of N for untreated slurry, a rise of 292%.

The improved nitrogen value a cow was £14.23 over four weeks and represented a total financial benefit in terms of N of £4982 a month for the 340-cow herd.

Roger Leach, herd manager at Myerscough College, described the results as “very encouraging”. “Soaring ammonium nitrate costs are making us review our fertiliser policy, so we’re keen to continue to monitor improvements in the treated slurry’s nitrogen value,” said Mr Leach.

Although SlurryBugs is an established product, its use has been restricted to a single treatment of underground slurry stores of a given capacity. The new SlurryBugs + SlurryBooster combination can now be used in outside lagoons where treatment is automatically administered daily at a given level.

And Ms Russell says the urine content of slurry has long been undervalued as a source of useable nitrogen. “Urine is not just waste liquid it contains a valuable source of urea, which in untreated slurry is converted to ammonia gas and can’t be measured. The bacteria treated with the inoculant are converting the urea into ammonia and then into organic nitrogen, which is where a lot of the additional nitrogen is coming from.”

Solar power

The inoculant is administered via a solar-powered micro-dispenser fitted to the side of the lagoon. The combined inoculant treatment is trickled into the lagoon at the rate of 150mg a day of each product.

The Myerscough herd’s system will involve treating 19.5m litres of slurry a year at a total cost of £2568, which includes all the inoculant required and the supply and rental of the automatic micro-dispenser. At a typical slurry application rate of 13,500 litres/acre (3000gal), the Myerscough lagoon will treat 118 acres each month.

The nitrogen contribution from inoculant-treated slurry will be 55.3kg/acre of nitrogen compared with 18.9kg/acre for untreated slurry. The value of treated slurry in kg/acre of nigtrogen would be 6525kg compared with 2230kg for untreated slurry.

In cash terms this could yield a value (based on ammonia nitrate at £400/t or £1.16/kg) of £18,702/ha (£7569/acre) compared with £6392/ha (£2587/acre) for land receiving untreated slurry – a difference of £12,310/ha (£4982/acre).