Tropical soil is not nutrient rich like many temperate soil regions. Soils beneath the forest vary, but the areas of good soils are small, apart from the flooded areas close to sediment-carrying rivers.
Relatively infertile, reddish latosols are common in Venezuela's Llanos and in the Guiana Highlands. Abundant moisture leaches some soils of all but the most insoluble minerals, including iron and aluminum sesquioxides, which are collectively known as laterite. The country's most fertile soils are formed by such well-drained, transported material as river alluvium or recent volcanic deposits.
Alluvial soils are found in the southern Maracaibo Lowlands, along the fringes of the Llanos, and in broad valley bottoms in the northern mountains. The Orinoco delta and adjacent plains are also rich in alluvium, although poor drainage in these low areas impedes agricultural development and discourages settlement. Volcanic soils cover the slopes of many of the northern mountains, but these fertile soils are often severely eroded because of deforestation associated with logging and the practice of shifting agriculture.
The geologically oldest formation is that of the acid Guyana shield to the south of the Orinoco River, frequently identified as the Pantepui Region, it extends into north-western Guyana and northernmost Brazil. The geology consists of a mainly granitic Precambian base the Guyana Shield, overlain by younger sedimentary sandstones and quartzites of variable thickness.
This gave rise to very infertile, leached soils that include:
(a) Soils of the flat-topped table mountains, the Gran Savanna, characteristically very sandy, with extremely low organic matter content.
(b) Mountain clay-sand soils, derived from granite and gneiss.
(c) Soils along the Orinoco River, influenced by alluvial sediments.
Along the more recent Andean region (the Andes, the Interior Chain and the Coastal Chain), soils are newer than those of the Guyana shield but have been altered by erosion, particularly in the piedmont, where human intervention has been drastic through deforestation.
In the oldest plains or Llanos (Eastern and Central Plains, and the Plains of the Meta River) oxisols predominate, frequently with very superficial horizons and an underlying ferrous layer. The more recent plains (Western Llanos, and South of Lake Maracaibo), some of the best soils are found. These are deep relatively fertile soils, though may have drainage limitations during the peak of the wet season.