Which characteristic defines the soil Order Alfisols?

Alfisols are characterized by a clay accumulation in their subsoil, which is a crucial aspect of their profile. This accumulation typically occurs in the horizon known as the argillic horizon. These soils generally exhibit a substantial level of base saturation, meaning that they contain a higher proportion of bases (such as calcium, magnesium, potassium, and sodium) compared to acids. This characteristic allows Alfisols to support a wide range of vegetation and agricultural activities, as they typically have favorable nutrient conditions due to their ability to retain cations.

Other options, such as high organic matter and sandy texture, do not specifically define Alfisols. High organic matter is more indicative of certain soil orders like Mollisols, while sandy texture is associated with soils that drain quickly and might not retain nutrients as effectively. Low nutrient availability is also not a defining feature of Alfisols, as the presence of clay and the high base saturation suggest that these soils can often provide good fertility for plants. Thus, the defining characteristic lies in the clay accumulation coupled with significant base saturation, making Alfisols distinct in their properties and usage in agriculture and land management.