Agricultural pollution is having a major effect on China's water supplies, according to the country's first national census of pollution sources issued on Tuesday.

The total discharge of Chemical Oxygen Demand (COD), a major water pollution indicator, was about 30 million tonnes in 2007, 43 percent of which was from agricultural sources, Zhang Lijun, vice minister of Environmental Protection, quoted the census as saying at Tuesday's press conference.

Zhang said controlling pollution from agricultural sources is essential to solving the country's water pollution problem.

Livestock and poultry are major sources of agricultural pollution, Wang Yanliang, an officer with the Ministry of Agriculture (MOA), said.

"We will solve the problem in accordance with the demands of modern agriculture and sustainable development," Wang said.

According to Wang, the MOA will work to help livestock and poultry breeding farms develop methane digesters.

As of 2008, the number of rural households using biogas in China hit 30.5 million, Wang said.

Measures will also be taken to limit the waste discharged in rural areas and improve the efficiency of agriculture chemicals.

Wang said free formula fertilization services will be provided to some 160 million rural households in 2010.

It took more than two years for over 570,000 staff to finish the census since the State Council made the decision in 2006 and the central government allocated 737 million (about 100 million U.S. dollars) for the project in 2007.

According to Zhang, a database for the census was established covering environment-related information of nearly 6 million objects nationwide as gists for administration and policymaking.

The census targeted nearly 6 million objects of industrial sources, agricultural sources, residential sources and centralized pollution control facilities, collecting 1.1 billion basic data on pollution sources.

Industrial pollutant discharges mainly concentrated in a small number of industries and areas, with prominent structural problems, Zhang quoted the census as saying.

"The census of pollution sources for the first time in the country is a significant survey on national situation. Its operations went smoothly and its main tasks were basically completed," said Zhang.

China faces big challenge of environmental deterioration amid its rapid economic development. Environmental experts had suggested that trustworthy statistics on the sources and extent of pollution was highly necessary for the country's effective and long-term pollution prevention and control.