Which soil characteristic is used to define alfisol suborders?

Alfisols are a type of soil classified primarily based on their horizon development, moisture regime, and associated properties. The suborders of Alfisols are indeed influenced by their drainage characteristics. The presence of well-drained conditions is essential for the formation and classification of these soils, as they typically develop under a range of climates but are often associated with more humid environments where effective drainage occurs.

The drainage characteristics directly impact the soil’s moisture retention, nutrient availability, and the biological activity within the soil. These factors contribute significantly to the soil's overall fertility and support agricultural productivity, which is a hallmark of Alfisols.

In contrast, while the other choices such as soil pH level, textural composition, and presence of clay minerals are important soil characteristics, they are not the primary defining factors for the suborders of Alfisols. These characteristics can vary widely within the alfisol classification and do not alone determine the suborder distinction.