Final answer:
A soil with poor infiltration is most likely high in clay, which has small particles and tiny spaces that limit water movement, contrasting with sandy soils that have better infiltration rates.
Step-by-step explanation:
A soil with poor infiltration would most likely be characterized by a higher content of clay. This is due to the fact that clay particles are very small, which results in a soil structure with tiny spaces between particles. These small spaces limit the movement of water, leading to slower infiltration rates when compared to soils with larger particles like sand. Although microbes and fungi can influence soil structure, they do not inherently cause poor infiltration. Conversely, sandy soils are known for better infiltration rates due to the larger pore spaces between sand particles that allow for rapid water movement.
As described in the provided information, clay soils have many small spaces that can hold water, while sandy soils have larger but fewer pore spaces. The high plasticity and cohesion when water is added to clay give it a denseness that further prevents quick water movement. This is supported by information that poorly drained soils tend to have reduced iron and darker color due to the accumulation of organic matter in anoxic conditions, which is a characteristic often associated with clay-rich soils.