China is being warned that it faces further environmental degradation from the overuse of chemical fertilizers, a bitter fruit its people are literally being forced to swallow, says a leading Chinese expert on the ecology.

It's the result of the country's long-boasted miracle of being able to feed 22 percent of the world's population with only seven percent of the world's arable land, said Gao Jixi, director of the Ecology Institute with the Chinese Research Academy of Environmental Sciences.

"It costs us dearly. Intensive use of chemical fertilizers and pesticides have led to severe soil, water and air pollution," he said.

Gao offered a grim list of agricultural side effects at a forum being sponsored by "Sino-Italian Green Week". "More greenhouse gases are being produced. Accumulating heavy metals are hardening the soil and reducing its fertility. Surface water is over-enriched with nutrients and groundwater is polluted by nitrates," he said.

Chinese farmers use 41.24 million tons of chemical fertilizers every year, for an average of more than 400 kg per hectare of farmland, far above the safe limit of 225 kg per hectare in developed countries, said Gao.

"Only 40 percent of nitrogen fertilizers, a heavily used chemical fertilizer in China, is being applied efficiently. Almost half of it evaporates or runs off before being absorbed by crops, causing water, soil and air pollution," Gao said.

Statistics show that from 1985 to 2000, China saw 141 million tons, or nine million tons per year, of nitrogen fertilizers washed away and turned into pollutants.

About 75 percent of the country's lakes and 50 percent of groundwater are polluted.