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Difficulty: HardSoil Types, Distribution, and Soil Conservation in Nigeria

In the Guinea Savanna zone of Nigeria, agricultural productivity on Ferruginous tropical soils derived from crystalline Basement Complex rocks is severely constrained by the seasonal formation of an indurated subsurface iron hardpan. Which soil management strategy is most effective for mitigating surface runoff erosion and restoring soil physical structure in this environment?

  1. Deep subsoiling combined with contour bunding and cover croppingAnswer
  2. B
    Continuous bush burning during the dry season to expose the hardpan to physical disintegration
  3. C
    Cultivating rainforest tree crops like oil palm and cocoa to naturally dissolve the subsurface hardpan
  4. D
    Flooding the farm plots continuously to transform the hardpan layer into alluvial sediments

Answer

Deep subsoiling combined with contour bunding and cover cropping is the most effective management strategy for Ferruginous tropical soils with subsurface iron hardpans.
The correct strategy uses deep subsoiling to mechanically rupture the rigid subsurface iron hardpan (plinthite), allowing rainwater penetration and deeper root growth. Pairing this with contour bunding retards runoff along savanna slopes, while cover crops prevent rain-impact crusting and replenish soil organic matter.

Step-by-Step Solution

1
Analyze the soil characteristics and pedological constraints
Ferruginous tropical soils in Nigeria's Guinea Savanna have rich iron content that hardens into an impermeable subsurface plinthite layer (hardpan) during marked dry seasons.
Understanding the physical barrier created by hardpan formation is essential for selecting appropriate soil conservation techniques.
2
Evaluate mechanical and biological conservation options suitable for this soil group
Mechanical subsoiling breaks the dense subsurface layer to allow root penetration and water infiltration, while contour bunds prevent slope wash and cover crops reduce surface crusting.
Combining mechanical disruption of the hardpan with surface water management provides a complete soil conservation solution.

Key Concept

Ferruginous Tropical Soil Characteristics and Conservation in Nigeria
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Topics

Soil Types, Distribution, and Soil Conservation in Nigeria

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