What is loam typically composed of?

Loam is a soil type known for its balanced mixture of sand, silt, and clay, making it ideal for agriculture and gardening due to its ability to retain moisture while providing good drainage and aeration. The composition identified in the correct choice, which consists of 40% sand, 40% silt, and 20% clay, reflects this ideal balance.

In loam, the substantial percentages of both sand and silt contribute to good aeration and drainage, while the clay helps in moisture retention. This combination results in a fertile soil type that promotes plant growth, making loam highly desirable in various landscaping and agricultural applications.

The other compositions lack this characteristic balance necessary for loam. For instance, a higher percentage of either sand or clay would lead to properties more akin to sandy or clay soils, which can either drain too quickly or retain too much moisture, respectively, thus not providing the optimal conditions represented by the correct answer.