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[BEIJING] The scourge of nitrogen pollution in China could be prevented by more efficient use of nitrogen fertiliser in farming — without compromising crop yields, researchers have found.

Farmers in China often practise 'double-cropping', where a second crop of food is planted in the same field after the first crop has been harvested.

This has allowed the country to achieve food self-sufficiency but the excessive use of nitrogen fertiliser, applied to each crop, can lead to environmental problems including the pollution of groundwater with nitrates, greenhouse gas emissions and other forms of air pollution — as well as harming the health of humans and ecosystems.

Because over-fertilising provides crops with more nitrogen than they need, up to twice as much is lost to the environment than with optimum methods, via different processes depending on the crop.

In a study published in the Proceedings of the National Academy of Sciences last week (16 February), researchers compared common fertilisation techniques with optimum techniques in two of the most intensive double-cropping systems in China: rice/wheat in the Taihu region of east China and wheat/maize on the North China Plain.

They found that average fertiliser use — around 600 kilograms per hectare — can be cut by 30–60 per cent, with farmers retaining the same yields.

By efficiently recycling manures and crop residues, and rotating crops with nitrogen-producing leguminous plants, it is possible to reduce reliance on synthetic nitrogen fertilisers, the researchers write.

The use of synthetic fertiliser has been actively promoted by scientists since the 1980s, and nitrogen fertiliser use has increased from seven million to 26 million tonnes today.

Ju Xiaotang, a professor at the College of Resources and Environmental Sciences at the China Agricultural University in Beijing and lead author of the research, suggests that the government educate farmers to avoid over-fertilisation and environmental degradation.

Zhang Shuqing, a researcher at the Institute of Agricultural Resources and Regional Planning at the Chinese Academy of Agricultural Sciences, said that farmers tend to use more fertiliser than necessary because they worry the crops will have insufficient nutrients.

"Balanced application of nitrogen, phosphate, potassium and micronutrient fertiliser will help reduce the pollution while maintaining a good effect on crop yield," says Zhang. 

Link to abstract in the Proceedings of the National Academy of Sciences


Proceedings of the National Academy of Sciences 10.1073/pnas.0813417106 (2009)