What defines a soil as an udalf?

A soil is defined as an udalf primarily based on its base saturation characteristics. Specifically, udalfs are characterized by having a base saturation of 60% or more within a specified depth, typically 25 to 75 centimeters. This level of base saturation indicates a soil that is more fertile and capable of supporting a greater biodiversity of plant life, as adequate base saturation usually correlates with the availability of essential nutrients for plant growth.

In the context of soil classification, the term "udalf" is part of the great group classification in the soil taxonomy system, which designates soils that are generally moist and exhibit a high nutrient base status. This is important for understanding soil management practices, as udalfs are often more productive due to their nutrient-rich character.

The other options reference soil characteristics that do not pertain to the defining criteria for udalfs. High clay content relates to soil texture, which influences water retention and drainage but is not a defining characteristic of udalfs. The presence of acid cations can indicate certain chemical properties of soil but does not classify it as an udalf. Likewise, base saturation below 60% would actually denote a different soil type, likely one that is less fertile and potentially more acidic, contrasting with