The sector of agriculture is vital to the economic development of Nigeria. The sector accounts for over a quarter of the gross domestic product (GDP) of the country and is responsible for over two-thirds of employment. The GDP is the market value of goods and services provided by a country in a period of time, normally this is produced on an annual basis. The GDP is vital to indicate the standard of living in a country. Nigeria is the leader in Africa when it comes to output from agriculture, and is ranked twenty-fifth in the world in the area. Having said that, the agricultural output is suffering from mismanagement, and the lack of basic infrastructure. Nigeria used to be a major exporter of four of its main products. These products are cocoa, rubber, palm oil, and groundnuts. The cocoa production has dropped in recent years from 300,000 tons per year to 180,000 tons per year. Nigeria used to be the largest producer of poultry in Africa, but the output of poultry has fallen by over 50% in recent years to about 18 million birds per year. This is because of import constraints, which in turn has affected the number of production units in food processing sectors. There is no long-term investment in technology in the sector so there is a lack of modern production methods, meaning old-style and less cost-effective methods are still being used. The main products produced by Nigeria are corn, cocoa, millet, palm oil, rice, yams, and tapioca. Livestock produced includes veal, beef, pork, poultry, and eggs. The situation regarding the lack of technology in agriculture means that the country is struggling to feed itself, and now has to rely heavily on imported food.