Which soil type retains water and might block fumigant movement?

Clay is the soil type that retains water and can significantly impede the movement of fumigants. This occurs because clay particles are very small and densely packed, creating a fine texture that leads to high water retention. The compact structure of clay enables it to hold moisture tightly, which, in turn, creates barriers to the diffusion of gases including fumigants.

When it comes to fumigation, this property of clay can hinder the effectiveness of the treatment, as the fumigant may not penetrate the soil as well as it would in coarser soils. The water-holding capacity of clay can also create conditions where the fumigant might be absorbed into the soil, rather than being available to move through the air space where pests may be present.

In contrast, sand has larger particles with greater porosity, allowing for quick drainage and more movement, while silt has intermediate properties, and loam is a mixture of sand, silt, and clay that tends to retain nutrients and moisture but does not impede fumigant movement as clay does. Therefore, when considering soil types in relation to fumigation effectiveness, clay’s ability to hold water and block fumigant movement makes it the correct answer.