Tuesday, November 6, 2012

China - Over-Fertilization In China Linked To Climate Warming, Study

A new study by the Chinese Academy of Sciences recommends a 60 percent reduction in fertilizer use in areas that are already ‘over-fertilized.’

AsianScientist (Nov. 5, 2012) – A new study by the Chinese Academy of Sciences recommends a 60 percent reduction in fertilizer use in areas that are already ‘over-fertilized.’

Halving the amount of nitrogen fertilizer used in certain areas of China would substantially decrease greenhouse gas emissions without affecting crop productivity and the area’s natural carbon sink, it says.

The study, which was published this month in the journal Environmental Research Letters, also pinpointed areas of heavy nitrogen fertilizer use as the North China Plain and middle and lower reaches of the Yangtze River Basin.

China is currently tasked with meeting the food demands of 22 percent of the world’s population; however, its over-reliance on nitrogen-based fertilizer has dramatically increased its emissions of nitrous oxide – the third highest contributor to climate change behind carbon dioxide and methane.

According to the study, since 2002, the warming effect caused by nitrous oxide emissions has been significantly greater than the cooling effects from the croplands storing carbon dioxide, resulting in overall warming.

Looking at the past six decades, the researchers found that between 1949 and 1990 nitrogen fertilizer increased the rates of crop production and the storage of soil carbon; however, from 1990 onward, they found that the rate of soil carbon storage stopped and the rate of crop production slowed.

In the 1990s, nitrogen fertilizer was contributing to 53 percent of the crop production but since then has contributed to 49 percent, even though more of it was being used, suggesting it had become less effective.

Nitrogen fertilizer can be beneficial to the climate, providing crops with essential nutrients so they can grow and create a larger natural carbon sink in soils, taking in excess carbon dioxide that is released into the atmosphere. When there is a balance between nitrous oxide release and carbon dioxide intake, the warming effects of nitrous oxide can be negated.

“Nitrogen fertilizers have become less efficient in recent years as the nitrogen input has surpassed nitrogen demands of plants and microbes. Excess nitrogen is not stimulating plant growth but leaving the system through leaching and nitrous gas emissions,” said Dr. Hanqin Tian, a co-author on the study.
Chinese farmers need to be educated on the economic and environmental costs of excessive nitrogen fertilizer use, says Tian.

“Effective management practices such as compound fertilizer use and optimized irrigation and tillage should be advanced to increase nitrogen use efficiency,” he advised.

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