China's reserves of phosphorus, a key element for growing food, could be exhausted within the next 35 years if the country maintains its current production rate, a new study has found.

However, China could delay exhausting its phosphorus reserves by more than 20 years through improving agronomic use efficiency of the mineral to the average level of 80 percent in developed countries without impairing current crop yields, said the study, published this week in the U.S. journal Proceedings of the National Academy of Sciences.

Zengwei Yuan of Nanjing University and colleagues modeled the phosphorous cycle in China since the 1600s and evaluated the mineral's potential for eutrophication, which may lead to algal blooms, plant overcrowding, and oxygen depletion.

They found China intensified its phosphorus mining, particularly during the last 60 years, to feed increasing populations and meet people's demand for animal protein.

In 2012, China's annual phosphorus extraction reached 12.50 million metric tons, accounting for over 40 percent of the global phosphorus production, they said. About 70 percent of the domestically exploited phosphorus was used to produce synthetic fertilizers.

The study revealed phosphorus overapplication by Chinese farmers. In 2012, China's crop production saw an average use of 80 kilograms of phosphorus per hectare, more than double the figure that crops can generally assimilate and far higher than the average level of the developed countries.

Meanwhile, only 4 percent of natural phosphorus resources were eventually ingested by Chinese residents in 2012, slightly lower than the 5 percent in the United States.

The researchers also found China has become a net phosphorus exporter since 2003, exporting mainly phosphorus-containing chemicals such as fertilizers and pesticides, while importing crops, specifically soybeans from the United States, Brazil, and Argentina.

As a result, phosphorous accumulated rapidly in China's surface waters and lands in the last decade.

The researchers' analysis showed that high phosphorous emission densities and their potential eutrophication effects occurred mainly in prosperous eastern coastal provinces, which have relatively higher population density.

The average phosphorous emission density in eastern China was 495 kilograms per square kilometer per year, eightfold higher than in western areas, according to the study.

"The findings showed that unreasonable exploitation and utilization of phosphorus resources is intensifying China's phosphorus crisis, with water eutrophication problem that comes with the crisis becoming increasingly apparent," Yuan told Xinhua. "Our work highlighted the importance and urgency of sustainable utilization of China's phosphorus resources." (Xinhua)