New rules governing ammonia emissions could see European farmers having to drastically alter the way slurry is spread.

The latest round of Integrated Pollution Prevention and Control (IPCC) regulations have a target of slashing ammonia outputs to the atmosphere by 8% by 2020.

Given that 95% of all production of the gas comes from livestock and biogas slurries, farming is likely to come under intense scrutiny, according to Danish environmental consultant Morten Toft.

“Agriculture is coming under the spotlight already here in Denmark but the IPPC is EU legislation so every member state is going to eventually have to conform,” he explains.

“We’ve spent a lot of time developing different ways of applying slurry, such as injectors, trailing shoes, and cultivator applicators, and they certainly help, but the fundamental science has been ignored until now.

“Ammonia losses are intrinsically linked to pH – and that’s the key to limiting them.”

“We’ve spent a lot of time developing different ways of applying slurry, such as injectors, trailing shoes, and cultivator applicators, and they certainly help, but the fundamental science has been ignored until now.”
Morten Toft, environmental consultant

Cattle and pig slurries tend to hover somewhere just below pH8 while biogas digestate can often be more alkaline than this. The higher the pH, the greater the amount of ammonia volatilisation.

So Mr Toft’s solution is simple – lower the pH in the slurry and ammonia emissions will be reduced.

“At a pH of 8 you’ll generally get ammonia levels of about 5% but because it is continuously being produced as it evaporates, losses can be as high as 80%.

“Bringing the pH down to 6 drops the amount in the slurry to about 0.01%.

“To do that we’ve developed a system to add sulphuric acid to slurry as it is applied.”

Called the Biocover SyreN, it consists of a front-linkage mounted IBC tank carrier with pH sensors, pumps and a mixing chamber that is fitted after the slurry macerator.

It injects between 1-1.5 litres of acid for every cubic metre of slurry, depending on its initial pH.

By doing so bicarbonates are released, creating bubbles of carbon dioxide in the liquid, which help to dissipate the liquid across the soil surface, according to Mr Toft.

“At €65,000 [£51,370], it is an expensive set-up – as a farmer you need to be handling at least 12,000cu m a year to make it pay.

“Generally it’s with contractors doing over 35,000cu m – they are charging an extra 50¢/cu m.

“We have 120 rigs out there working. Of course the big advantage to farmers is that they’re not losing valuable nitrogen.

“Denmark has managed to halve its consumption of mineral fertiliser in the past 20 years while increasing crop yields. In the main that’s down to better use of animal slurries – SyreN is just the next step in this.”