HONG KONG, Feb 17 (Reuters) - Excessive use of nitrogen fertilisers in China in the past few decades has polluted its groundwater, given rise to acid rain, soil acidification and increased greenhouse gas emissions, Chinese experts said.
In their article published in the Proceedings of the National Academy of Sciences, they urged farmers in the country to reduce their use of synthetic nitrogen fertilisers and change their farming practices.
"Integrated management packages ... include efficient recycling of manures and crop residues, the use of legume crops in rotation to increase internal nitrogen cycling and further reduction in the reliance on synthetic nitrogen fertilisers," they wrote.
Overuse of synthetic nitrogen not only happens in China but in many other Asian countries which are under pressure to feed large and growing populations.
The study showed that while annual grain production increased to 484 million tonnes in 2005 from 283 tonnes in 1977 in China, its use of synthetic nitrogen fertilisers ballooned to 26.21 million tonnes from 7.07 tonnes over the same period.
In China, scientists and the government strongly encouraged the use of nitrogen fertilisers until the 1990s, when they realised the serious damage it caused to the environment but they have been unable to reverse the practice.
"Persuading farmers to limit fertiliser inputs is difficult because many of them still hold to traditional opinions that higher crop yield will be obtained with more fertilisers," wrote the team, led by Ju Xiaotang at the College of Resources and Environmental Sciences in Beijing.
However, they stressed: "Only by reducing fertiliser nitrogen inputs can degraded environments be gradually restored, enhanced and protected."
They also called for the introduction of certain legislative controls in China, similar to the ones in the European Union.
* removing government subsidies
* introducing a nitrogen fertiliser tax
* educating farmers on environmental awareness
* employing practices that avoid serious environmental degradation (Reporting by Tan Ee Lyn; Editing by Sanjeev Miglani)