The relief

Tunisia North-West is located in the extension of the Atlas mountain range which starts in southern Morocco and is divided into two rows facing east-west: the Tell Atlas following the Mediterranean coast and the Saharan Atlas fading arriving in Cap Bon and the Gulf of Hammamet to the sea.

Between the north coast and the valley of the Medjerda the Northern Tell is in the form of three lesser high rows, reaching the eastern coastline between Cape Blanc and Ghar El Melh, which are: the mountains of Khroumirie (rising to 1000 m), Nefza Mountains (rising to 600 m) and Mogods (rising to 500 m).

South of these mountains, the valley of the Medjerda is served by several wadis (Mellègue, Tessa, Beja, Zarga), then follows the hilly area of the Monts de Téboursouk between the city of El Kef and the Gulf of Tunis: the Higher Tell.Further south, the Tunisian Ridge stretches from west to east, from the Mountains of Tebessa to the Algerian border, to Cap Bon on the eastern coastline. It consists of mountain ranges alternating with steep plateaus and depressions: Djebel Chaambi (1544 m), Jebel Semmam (1314 m), Djebel Serj (1347 m), Jebel Zaghouan (1295 m), Djebel Sidi Abderrahmane in the Cap Bon (637 m).

Further south the Ridge, the Saharan Atlas is reduced to a few units scattered throughout the mountainous high steppes: Djebel Mghilla (1378 m), Jebel Selloum (1373 m).The region of high plains to the west and low plains to the east is crossed from west to east by a few isolated mountains: Djebel. Majoura (874 m), Djebel. Bouhedma (790 m), Djebel. Orbata (1165 m), Djebel. Asker (608 m).

South of Gafsa major depression Chotts mark the beginning of the horizontal part of the Sahara. South of the Chott to the ends of Dahar, the Grand Erg Oriental is extended.

The Dahar Mountains, the plains of Jeffara and El Ouara complete the landscape of southern Tunisia near the eastern Mediterranean with the island of Djerba.

Soils

Bioclimatic diversity, geological and morphological diversity combined with diversified soils (natural vegetation, rainfed crops and irrigated crops) is at the origin for the existence of a mosaic of genetically different soils.

These soils are faced with convergent natural factors (soft rock, steep slopes, sharp showers, sparse vegetation cover) that are responsible for the state of degradation. This is essentially the water and wind erosion, and salinization.

Three main regions are distinguished by the nature of their soils and modes of exploitation of their land.

Northern Tunisia

It is divided into two parts, the North West and North East:

• The first, which is an agro-forest-pastoral region, is distinguished by hydromorphic soils and acid brown characteristic of the Kroumirie Mogods mountain and Calcimagnesian (Rendzinas and brown limy types of soil) covering the slopes of the glacis and the Tell vertisols; and associated with slightly evolved soils with more or less hydromorphic alluvial aspect , forming floodplains (The Upper Valley of Medjerda.).
• The second part is the north east, land has very diverse Rendzines: red soil, brown soil, forming a mosaic of soils occupying the glacis and the slightly developed and quite healthy slopes and soils on the plains. Holomorphic soils are confined to depressions and "Garâas". There are also the eroded raw mineral soils associated with brown soils covering the most prominent slopes (Jebel Abderrahmane).

Central Tunisia

It is an agro-pastoral region, dominated equally by:

• The heavy soils of the alluvial plains much of which is halomorphic (Lower steppe);
• Encrusted limy and skeletal soils of the great glacis of the High Steppe (alfa), 
• The deep and light soils of the Gammouda / Meknassy region where there was a rich course of the past that is almost completely converted to arboriculture (olive, almond, etc.)..

Southern Tunisia

It is a pastoral region distinguished by the presence of numerous oases around the water points. It is characterized by:

• Slightly eroded hills, except for the Matmatas chain where anthropogenic soils are created behind dams called "Jessours" established through the many ravines whereby water and soil are collected and used intensively in arboriculture (olive trees);
• The coastal plains (the Jeffara) where we find encrusted glacis upstream and sierozems and slightly developed soils downstream. Depressed parts are occupied by gypseous and halomorphic soils.
• The large depressions or "Chott" are occupied by very salty and barren soil. Around them we find wind ridges (Dhraa), formed by deep sandy soils and occupied by the best oasis (Tozeur, Degache);
• The desert area, formed by Erg (succession of sand dunes) and Dhar where the soil is completely bare and stony (Reg).