What is a key characteristic of loam soil?

A key characteristic of loam soil is that it contains an equal mixture of sand, silt, and clay, which allows it to retain moisture while also providing good drainage and aeration. This balanced composition is ideal for agriculture as it supports a wide range of plant growth by providing essential nutrients, good water retention, and sufficient drainage to prevent root rot.

While choice C specifies a particular composition of 40% sand, 40% silt, and 20% clay, this specific ratio does not fully represent the true defining characteristic of loam. Generally, loam is defined by its balanced mixture rather than a strict percentage breakdown. Thus, the essence of loam lies more in its homogeneity and the equal functionality of its components rather than in a precise numerical formula.

The other options describe soil types that do not meet the balanced characteristics typical of loam. For example, having only sand and clay fails to include silt, which is crucial for defining loam. Additionally, when clay dominates, it can lead to poor drainage and aeration, characteristics that are not favorable for many plants.