The authors of a new report, Nitrogen UK, which confirms agriculture as the biggest user of nitrogen, are calling for continued improvements in farming practices to tackle the problem of nitrogen-based pollution.

Commissioned as part of the Biffaward programme on sustainable resource use, the report by Robert Lillywhite and Clive Rahn of Warwick HRI points out that while agriculture is the biggest producer of nitrogen-based pollutants, it’s the inherently poor conversion rates between nitrogen supply and nitrogen assimilation which cause the main problem, rather than the actions of individual growers or the continued overuse of nitrogen fertiliser.

But, they say, more can be done on farm to mitigate nitrogen pollution.

The report also identifies the combustion of fossil fuels for power generation and in vehicles as being responsible for the release of large amounts of reactive nitrogen into the environment.

And poor information from some sectors, most notably the chemical industry, mean that there are large gaps in understanding.

“It’s important to have an understanding of the bigger picture when studying nitrogen and its use,” stresses Mr Lillywhite.

“Nitrogen is an essential element and an integral part of all plants and animals.

“But it’s also a pollutant. Nitrate from both agriculture and sewage promotes eutrophication, while the gaseous products, nitrogen and nitrous oxides from combustion contribute to global warming.

“So while it’s essential, it is also a problem.

And that’s on a global scale, rather than just in the UK and Europe.”

The report, which was launched in London last week, recognises the role of better farming practices in reducing nitrogen losses and the recent introduction of legislation to improve application methods and timings.

“Agriculture has a unique problem in that it produces lots of waste,” Mr Rahn explains.

“That waste contains a great deal of nitrogen.

The ultimate aim must be to use inputs more wisely and efficiently, so that we have minimal amounts of environmental pollution and waste.”

Cereal production is the most efficient farming sector, utilising 57% of its nitrogen, while beef production is the worst at just 13%.

Plants recover, on average, 50% of the nitrogen applied as fertiliser, while beef cattle recover only 9% of nitrogen contained in feed.

“The biggest contributors to the UK’s ammonia emissions are cattle,” he confirms.

“The other issue with livestock production is manure, which although it contains large and valuable amounts of nitrogen, is too often lost to the atmosphere and to rivers via leaching, without being used by a growing crop.”

Mr Lillywhite says nitrogen losses to the environment from farming come in many forms.

“We’ve all heard about nitrate leaching in soil water.

But there’s also gaseous nitrous oxide and ammonia produced from soil processes, nitrous oxide released from the breakdown of fertiliser, volatilisation of ammonia from slurries and manures and nitrogen oxides from the use of agricultural machinery.

“We have to recognise that agriculture is responsible for the greatest leakage of nitrogen to the environment.

This is not deliberate, but a result of unavoidable inefficiencies.”

He notes that recent work has concentrated on improvements in livestock housing to reduce ammonia emissions and better tillage techniques to limit nitrous oxide emissions.

“These are the sort of areas where we must continue to act.

Nitrogen is potentially more damaging on a global scale than carbon dioxide.”

fwarable@rbi.co.uk