Which horizon's texture is critical for determining shrink and swell potential in soil?

The shrink and swell potential of soil is primarily influenced by the texture of the soil, particularly in the horizons where clay content is significant. Both the A and B horizons can contain clay, which is key to assessing how much a soil will expand when wet and contract when dry.

The A horizon, or topsoil, typically has a mix of organic matter and minerals, and its texture can encompass a range of particle sizes, including sufficient clay content that affects water retention and swelling potential.

The B horizon, or subsoil, often accumulates clay leached from above layers during the weathering process and may have higher clay content compared to the A horizon. The texture here is especially crucial as it contains material that has moved down and can indicate significant shrink-swell characteristics.

By evaluating the texture in both the A and B horizons, you can better understand the soil's behavior regarding shrink and swell mechanisms. Thus, both horizons play a role in this assessment, making the choice encompassing both correct.