Soil distribution
Mauritania exhibits five types of soils. As rain is as insignificant as irregular in the great part of the territory’s landmass and the magnitude of the gap between maximum and minimum temperature being such as physical modification of rocks remains mainly unchanged, Mauritanian earth is mostly without vegetal life. Thus, soils are typically characterized as “weathered raw-mineral soils” or lithogenic soils. These weathered raw-mineral desert soils are classified in two parts, namely; 1) desert deposited soils and, 2) desert ablation soils. The first type of soils is found in the great ergs; which are widespread surfaces of sands deposited by wind and superimposed one on the other without any stratification. The second type of soils develops on rocks which have been altered in the past. They shape regs of coarse sands, gravels or pebbles as a result of wearing rocks by and through wind activities (Eolian weathering). These activities have been very differentiated throughout ages. Accordingly, certain soils formed in the quaternary under conditions of humidity which are presently not existing. Thus, in the north-west, there are regions with paleo soils, brownish resulting from calcareous earth or covered by a limy crust. In this same region, these desert ablation soils are often found together with so-called deposited soils, laid down through ancient rivers which have presently disappeared.
In the neighboring category, there are the so-called “raw mineral soils’’ resulting from alteration of diverse less or not decomposed rocks. Qualitatively, they are very poor, less thick and roots of plants have great difficulties to penetrate their ground. Practically, they have no value for any plant life
A part from the above type of soils, much younger soils constitute the second category. They are still in their process of growth which are thicker, resulting either from climatic origin taking shape on sedimentary rocks or on sandy ground brought by wind. And there are those developing on sandy coastal sands independently of climate.
The third category is found in the semi-arid zones. They are known as isohumic and are characterized by a relatively higher proportion of humus resulting from the decomposition of vegetal and animal elements apart from a sufficient content of iron giving it a reddish color. They are younger soils or less developed soils.
The fourth class of soils is that whose characteristics are due, in great part, to the temporary or permanent presence of water. They are, thus, called hydromorphous soils. It occurs only in the Southern part of the country in the form of a band stretching along the Senegal river. They are known as hydromorphous soils.
Finally, the fifth class is made by halomorphous soils meaning characterized by the presence of sodium, potassium and/or solvable chemical composition. They are found in the coastal region or in some basins without flow to the ocean. As such, they are very compact and waterproof and the presence of the above signaled chemicals makes them totally inappropriate to agriculture.