TeXes Science Practice Test

Which soil type is characterized by strong leaching and low organic matter?

1. Mollisols

2. Aridisols

3. Ultisols

4. Oxisols

The correct answer is: Ultisols

The chosen answer is characterized by its tropical or subtropical climate, where heavy rainfall leads to strong leaching of nutrients. This process washes away minerals and organic matter from the surface layers of soil, resulting in a profile that often exhibits low levels of organic material. Ultisols typically have a clay-rich subsoil, which can retain some nutrients, but they are still recognized for their leached, nutrient-poor upper layers and are often acidic. Mollisols, on the other hand, are known for their rich organic matter, especially in the upper horizons, making them fertile and well-suited for agriculture. Aridisols are typically found in arid regions and may have some leaching, but they tend to retain more salts than nutrients. Oxisols, often found in tropical regions, can also be heavily weathered and leached, but they usually contain higher levels of iron and aluminum oxides and can still support more organic matter than Ultisols. Therefore, Ultisols uniquely fit the characteristics of strong leaching and low organic matter due to their formation processes in humid climates.