Cultivators are again growing high-quality rice
The most important methods, dieri and oualo,
were entirely dependent on limited and erratic rainfall and on the annual flooding of the Senegal riverand its only perential tributary in Mauritania, the Gorgol river.Dieri cultivation occurred during the rainy season, from June-July to Sep-Oct,in areas receiving sufficient precipitation (400-450 milimitres annually) to grow millet and peas.Oualo plantings occurred during the cold and dry season from Nov-March, to take advantage of ground moisture as the flood waters of the Senegal and Gorgol rivers receded. Sorghum was the major crops for this season. Oasis cultivation drew its water from subterranean sources and so was not dependent on rains. Indeed, areas were oasis were located might experience any signicant rainfall for the years. Modern irrigated agriculture was only partially dependenton annual rain fall.It dependent primarily on the dams to to retain water from the annual rise of waters of the rivers. For the Senegal river, these rains fell principally in the headwaaters in eastern Mali and Guinea.
The two major droughts of the African Sahel were
prolonged in Mauritania by intermitent dry spells.The result was a serious decline in overall agricultural production. In the 1960s mauritania had produced about one-half of its grain needs.By the 1983-85 period, again harvests had fallen to a level that met only about 3 to 8 p.c. of the country's grain needs. The cereal deficits have been filled through a combination of commercial imports and international food aid, of which USA has been the principal donor. During the most serious drought years from 1983-85, food aid accounted for over 61 p.c. of Mauritania's available supply of grain, Local production covered only 5 p.c. of the need. The rest has to be procured from international sources either by purchase from private or state sources. In the next three years production was much better. 
