China launched a month-long promotion campaign Saturday for its second agricultural census, the world's largest.

The census provides the foundation for improving the country's rural policies, said Xie Fuzhan, head of the National Bureau of Statistics, at the launch ceremony.

The national investigation will last from January 1 next year to the end of April, covering more than 200 million rural households and employing over 7 million investigators.

Information will be collected mainly through on-the-spot inquiries about agricultural production, employment, migration, environmental conditions, use of land, fixed-asset investment and quality of life in rural areas.

The promotion campaign is designed to make people understand the significance of the census and fully cooperate with the investigation, said Xie.

China carried out the first agricultural census in 1996.

Since then, the Chinese government has adopted a series of policies to protect farmer's interests, including abolishing agricultural taxes, providing subsidies and setting a minimum price for grain and a maximum price for fertilizers.

Official data show the per capita cash income of Chinese farmers in the first nine months of the year reached 2,762 yuan (US$345), up 11.4 percent year on year.