Sudan's climatic conditions (mainly the rainy seasons) enable double annual harvests (in July and November) in the southern parts of the country. Most of the agricultural activities are concentrated near the Nile River. The El Gezira irrigation system that is located between the White and the Blue Nile Rivers (both rivers merge to form the Nile River) is the most important agriculture project and, according to some statistics, is also the largest artificially irrigated region in the world. As the irrigation system has been put in place, sorghum, wheat, and groundnuts have been planted instead of cotton in an effort to make Sudan self-sufficient in foodstuffs. The agricultural sector is the most important economic sector in Sudan. It created 39 percent of the gross domestic production (GDP), employed about 80 percent of population, and contributed 80 percent of the country's exports in the late 1990s. Cotton is the main agriculture export item, although its export volumes have been decreasing recently. The lack of any marketing or developed market policy is evident. The government has suggested the end of export taxes in order to promote more agriculture products in the future. Other agricultural products include sesame seeds, sorghum, and gum Arabic. Animal husbandry represents a very important part of the national economy, as well. Its production increased during recent years as a result of better veterinary treatment, better credit policy, and higher prices in the market. Fishing is another important sector of the national economy.