27 November 1998

Straw-based bedding threat to ozone layer

DEEP litter straw yards for pigs may be viewed as welfare friendly, but new research shows they could pose a threat to the environment by contributing to greenhouse gases.

Preliminary results from a series of MAFF-funded projects at ADAS Terrington shows up to 40% of available nitrogen is lost in the form of ammonia gas from some straw-based systems compared with just 30% from slurry-based systems.

ADAS senior research consultant Roger Kay says results from the first winter 10-week housing period indicates straw-based systems produce 2.2kg of ammonia N a pig compared with 1.2kg a pig for slurry-based systems. These losses could be higher during summer.

"Straw bedding is a good environment from which ammonia can be liberated. Pigs urine is held in moist straw and as this composts, building up heat, ammonia is emitted. But the total ammonia loss is determined by heat within a building and ventilation rate," he says.

The project – for the Rural and Marine Environment Divison of MAFF – will also measure nitrogen losses from storage and spreading for both solid FYM and slurry.

Research at Terrington will manage muck heaps by storing FYM in a similar manner to grass silage. Solid manure will be ensiled in a traditional silage wedge to control aerobic breakdown. These manure heaps will be covered with polythene so emissions can be measured.

But Mr Kay says ammonia losses wont just be associated with pig manure. Researchers at IGER North Wyke, Devon, will look at nitrogen losses from straw-based systems for beef as part of the same project.

The project should outline best practices for minimising nitrogen loss from manure and slurry, such as incorporating liquids and solids immediately after application. This should improve the use of muck as an organic fertiliser. The project will be completed by the end of next year.