What is the primary characteristic of loess soil?

Loess soil is primarily characterized by its silty or silty clay texture, which is formed from wind-blown silt. This fine-grained material contributes to its unique properties, such as good agricultural fertility and a relatively high water retention capacity. The predominantly silt content is crucial because it allows loess to hold moisture well while also providing a loose structure that is beneficial for root penetration and aeration.

In contrast, other options present characteristics that do not align with loess soil. For instance, a coarse sand content would indicate a different soil type that is coarser and does not retain water as effectively as loess. A high clay concentration describes a soil with a significant amount of clay particles, leading to different drainage and aeration properties. Exclusively organic material refers to soils primarily composed of decomposed plant and animal matter, which is not representative of loess. Thus, the defining trait of loess being its silty or silty clay texture underscores its formation process and environmental significance.