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.

China is also suffering serious side-effects of chemical pesticides, which has been deemed as the most effective means combating plant diseases and pests in decades.

"Overuse of pesticides has destroyed the ecological balance and biodiversity in cropland. Pesticide residue deposited in farm plants may poison humans and livestock," Gao said.

"Many farm produce are blocked or returned in foreign trade for failing to meet standards in pesticide use, resulting in millions of yuan of economic losses," Gao said.

China reported an annual use of more than 1.2 million tons of pesticides, which has contaminated 7 percent of its arable land.

Plastic films have been widely applied in farming in China. But Gao noted that most of the films are undegradable and may hinder roots to absorb water and prevent groundwater from oozing.

Even degradable mulch remnants will generate new toxicants during their decomposition, he added. China produces 1 million mulch films every year, about 10 percent of which are left in soil after use.

Gao also pointed out that 90 percent of China's livestock breeding farms haven't undergone any environmental impact assessment and 60 percent are short of necessary pollution prevention and control facilities.

China should realize sustainable development of agriculture by reducing use of fertilizers, employing integrated pest prevention and management system and using biodegradable mulch films, he said.

"We should take the entire farm ecosystem into consideration and make the best use of natural factors against plant diseases and pests." Gao said.

"Sino-Italian Green Week", co-held by Chinese and Italian governments, will put on show a series of activities, such as environmental forums and exhibitions of Italian architecture and design, from July 3 to July 6.