Which color indicates the presence of a spodic horizon in soil?

The presence of a spodic horizon in soil is indicated by a gray color. A spodic horizon typically develops in acidic sandy soils and is characterized by illuviation of iron, aluminum, and organic matter. This process results in a leached, low-nutrient layer that often appears gray due to the depletion of iron oxides, which contribute to darker colors. The gray color signifies the loss of these minerals and the environment's highly leached condition.

In contrast, other colors mentioned are not typically associated with a spodic horizon. Dark brown often indicates a rich organic content or fertile soils, red suggests the presence of iron oxides and well-drained conditions, while white indicates a high level of quartz or calcium carbonate, which are not characteristic of the spodic horizon. Recognizing these color indicators is crucial for soil classification and understanding soil formation processes.