Although it is a large country, most of Mauritania is desert. In the late 1980s, arable land was scarce, and, except for some oases, crop production was limited to a narrow band along the southern borders with Senegal and Mali. Farmers practiced four types of agriculture: rain-fed dryland cropping, called dieri; flood recession cropping along the Senegal River and its seasonal tributaries, called oualo; oasis cultivation, the least important; and modern irrigated agriculture.