Scientists find cause of nitrate leaching
SCIENTISTS at the University of Aberdeen have come up with an explanation how ammonia in fertilisers is converted to nitrate, which is then washed out of soils before reaching the intended crops.
Billions of pounds are spent annually on nitrogen fertilisers to support crop production, but huge increases in the world’s population in the next 50 years is set to double the amount of fertiliser used.
Much of this fertiliser is based on ammonia but more than half of this is lost to agriculture through the activities of ‘ammonia-oxidising’ microbes in the soil, which rapidly convert ammonia to nitrate, which is then washed away.
However, the scientists have shed new light on how ammonia-based fertilisers are inactivated by such micro-organisms.
They have found, 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 100 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 way such loss of fertiliser occurs in these soils has remained a mystery.
In two separate papers published recently in the journal Proceeding 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 it is abundant in acidic soils worldwide.
A large part of the research involved the analysis of soils from long-term pH gradient soil plots at the SAC’s Craibstone Estate outside Aberdeen.
Prof Jim Prosser and Dr Graeme Nicol at the University of Aberdeen have been studying these organisms in soil for over a decade, and have been investigating whether Archaea, an ancient evolutionary lineage of microbes, discovered in 2005, could be the missing link in the essential biogeochemical process in acid soils.
In a separate study, postdoctoral researcher Dr Cecile Gubry-Rangin, from the same research team, used state-of-the-art sequencing technology to demonstrate this organism is also dominant in acidic soils throughout the world.
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 physiology of the organism and to find out more about its potential role in the loss of ammonia-based fertilisers and nitrous oxide gas emissions from soil.