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UK Scientists Discover Cause of Nitrate Leaching

09 January 2012

UK - Scientists at the University of Aberdeen have worked out an explanation for how ammonia in fertilisers is converted to nitrate, which is then washed out of soils before reaching the intended crops.

Organisms that oxidise ammonia were first discovered in 1890. Although a natural process, a major consequence of the activities of such organisms in soil is the transformation and loss of nitrogen fertilisers used to improve crop production, resulting in groundwater and atmospheric pollution.

Over the past hundred years, all the strains cultivated have only grown in standard laboratory conditions at higher, neutral pH, and not in acidic conditions.

However, the majority of Scottish agricultural soils - and 50 per cent of the world's agricultural soils - are acidic, so the mechanism by which loss of fertiliser occurs in these soils has remained a mystery until now.

In two separate papers published recently in the journal Proceedings of the National Academy of Sciences USA, research performed at the University of Aberdeen has identified a novel organism which performs the process of ammonia oxidation in acidic conditions, and has also demonstrated that this organism is abundant and globally distributed in acidic soils.

A large part of this work involved the analysis of soils from the Scottish Agricultural College's Craibstone Estate outside Aberdeen, where their long-term pH gradient soil plots represent one of the few long-term experiments of its kind in the world and an extremely valuable resource for looking at the activity of organisms in soil.

To recognise the importance of the site from which the organisms were obtained, and the university at which the microbe was first cultivated, the new organism has been named Nitrosotalea devanaterra, which means an ammonia-oxidising ‘rod'from soil in Aberdeen, incorporating Devana, the Roman name for Aberdeen. It is part of the Domain of microbes known as Archaea.

The research team has now been awarded a £0.5 million, 3.5-year research grant by the Natural Environment Research Council to investigate the highly unusual physiology of Nitrosotalea devanaterra and to find out more about its potential role in the loss of ammonia-based fertilisers and nitrous oxide gas emissions from soil.

Billions of pounds are spent annually on nitrogen fertilisers to support crop production to feed the world's population. Predicted population growth in the next 50 years will require double the amount of fertiliser used globally. Much of this fertiliser is based on ammonia but unfortunately more than half of this is lost to agriculture through the activities of soil microbes.

These ‘ammonia-oxidising' microbes rapidly convert ammonia to nitrate, which is washed out of the soil before it reaches crops for which it is intended. This leads to losses to farmers estimated at over $15 billion per year and nitrate-polluted drinking water. Ammonia oxidisers are also responsible for production of nitrous oxide, a potent greenhouse gas that contributes to destruction of the ozone layer.

TheCropSite News Desk

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