Question

Difficulty: Very hardSoil Types, Distribution, and Soil Conservation in Nigeria

A soil scientist conducts a field transect across Nigeria, traveling along a direct line of longitude from the southern coast along the Gulf of Guinea up to the northern boundary with Niger Republic. Arrange the following major soil groups in the precise sequential order in which they are encountered from South to North.

  1. 1Saline and freshwater Hydromorphic soils of coastal swamps and river deltas
  2. 2Deeply weathered, strongly leached Ferrallitic soils (Acid Sands) of the rainforest belt
  3. 3Rich reddish-brown Ferruginous tropical soils developed over Crystalline Basement Complex rocks
  4. 4Shallow, sandy Regosols and desertic brown soils formed from aeolian wind-blown deposits

Answer

The correct South-to-North sequence begins with coastal Hydromorphic soils, followed by rainforest Ferrallitic soils, middle-belt Ferruginous tropical soils, and ends with northern semi-arid Regosols/brown soils.
The latitudinal gradient of climate and vegetation across Nigeria directly controls soil formation from south to north. The sequence starts at the Atlantic coast with waterlogged Hydromorphic soils, transitions to heavily leached Ferrallitic soils under the southern rainforest, moves into seasonally dry Ferruginous tropical soils in the Guinea Savanna, and concludes at the northern arid border with wind-deposited Regosols and brown soils.

Step-by-Step Solution

1
Identify coastal low-latitude soil belt (4°–6°N)
The southernmost zone consists of waterlogged deltaic and mangrove environments giving rise to Hydromorphic soils.
High water tables and tidal inundation at the coast prevent profile differentiation and produce gleys and alluvial deposits.
2
Identify humid rainforest soil belt (5°–8°N)
Moving inland, heavy precipitation causes intense leaching resulting in deeply weathered Ferrallitic soils (Acid Sands).
Abundant rainfall removes soluble bases, leaving iron and aluminum oxides in the subsoil.
3
Identify sub-humid savanna soil belt (8°–11°N)
In the Middle Belt, seasonal wet-dry savanna conditions foster Ferruginous tropical soils over crystalline rocks.
Moderate leaching with distinct dry seasons causes iron accumulation and plinthite/laterite layer formation.
4
Identify semi-arid northern soil belt (11°–14°N)
At the northern border, scanty rainfall and wind action yield sandy Regosols and brown soils derived from desert drift.
Harmattan winds bring aeolian sand deposits where chemical weathering is minimal due to low precipitation.

Key Concept

Latitudinal Zonal Soil Distribution in Nigeria
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