What soil order is characterized by significant clay accumulation and a base saturation of 35% or more?

The soil order defined by significant clay accumulation and a base saturation of 35% or more is Alfisols. This soil type is typically found in temperate regions and is known for its fertile characteristics, which make it suitable for agriculture. The presence of clay in the horizon is a result of weathering processes and contributes to good water retention, nutrient availability, and overall soil fertility.

Alfisols often develop from parent materials that are rich in minerals, and the clay accumulation leads to a distinct horizon that can have substantial amounts of cations available for plant uptake. The base saturation level of at least 35% indicates a balanced availability of nutrients, allowing for healthy plant growth. This makes Alfisols very efficient for agricultural practices.

In contrast, other soil types listed are characterized by different properties: Oxisols usually have low fertility with high weathering and clay that is often dominated by iron and aluminum oxides; Ustolls are typically associated with semi-arid environments and have lower organic matter; while Ultisols are characterized by high weathering and a lower base saturation, typically making them less fertile than Alfisols.