BEIJING -- About 37.1 percent of Chinese land area, or 3.56 million square kilometers, is suffering from soil erosion, with about 5 billion tons of soil eroding away annually, said China's top environment watchdog.

"Most soil erosion have taken place in the country's mountainous area and sandstorm-hit regions, especially at the upper and middle reaches of rivers," shows a "communique on China's 2005 environment condition" which was published recently by the State Environmental Protection Administration (SEPA).

It said among the 3.56 million square kilometers of soil erosion land, 165 million is eroding by water, another 191 million by wind.

Human activities are also reducing China's plowland area.

Statistics show that from 1998 to 2005, the country's plowland has been decreased by 7.6 million hectares, 1.42 million hectares of which are occupied by construction. About 2.13 million hectares of plowland has been restored after land rectification and improvement.

Around 10 million hectares of China's arable land, or more than one tenth of the country's total cultivated land, have been polluted by chemical fertilizers, pesticides, plastic films or dirty water, according to the SEPA.

Most of the polluted arable land is located in the country's economically developed areas, it said, adding crops damaged by heavy metals amount to 12 million tons each year, causing economic losses of 20 billion yuan (2.5 billion U.S. dollars) in China.

China has about 120 million hectares of arable land, 13 percent of its land area.