What best describes soil crusts in dryland soils and their impact on infiltration and seedling establishment?

• A. Soil crusts are solely formed by wind action and do not affect infiltration.
• B. Biological crusts are formed by biocrust organisms but physical crusts do not form from raindrop impact.
• C. Physical crusts form from raindrop impact; biological crusts are formed by biocrust organisms; both reduce infiltration and impede seedling emergence.
• D. Biocrusts enhance seedling establishment by improving infiltration.

Answer: (C)

Surface crusts in dryland soils come in two main kinds: physical crusts that form when raindrop impact seals surface aggregates into a hard, low-porosity layer, and biological crusts produced by biocrust organisms that bind particles into a cohesive, crusty surface. Both types limit water entering the soil and create a barrier seeds must push through, so infiltration is reduced and seedling emergence is impeded. In this context, recognizing that physical crusts form from raindrop impact and biological crusts form from biocrust organisms, with both reducing infiltration and hindering seedling establishment, best matches how these crusts affect dryland soils.