What indicator can suggest that soil is poorly drained?

The presence of mottling in the soil profile is a significant indicator of poor drainage. Mottling refers to the various colors or spots found in the soil, typically due to variations in moisture levels and oxidation processes. In poorly drained soils, saturation can lead to anaerobic conditions, which in turn affect the iron content and other oxidized minerals, resulting in the characteristic mottled appearance. This pattern indicates that the soil has experienced alternating periods of saturation and dryness, which is commonly associated with wet conditions and impediments to drainage.

Other indicators, such as high organic matter, may suggest soil health and fertility rather than drainage status. High soil temperature does not directly relate to drainage conditions and can vary independently based on factors like climate and soil cover. Similarly, a rich dark coloration throughout the soil often points to high organic matter content, which can be present in various drainage conditions. However, it does not specifically indicate poor drainage like mottling does. Therefore, mottling stands out as the key indicator for identifying poorly drained soils.