Which of the following is decreased by soil compaction?

Soil compaction negatively impacts several soil properties, notably reducing soil aeration. When soil is compacted, the spaces between soil particles decrease, leading to a denser soil structure. This reduction in pore space significantly limits the movement of air within the soil, which is crucial for the respiration of plant roots and beneficial soil microorganisms.

Although nutrient availability can be affected by compaction, it is essential to understand that the primary issue with compacted soil is the lack of aeration. Without proper aeration, root growth is hindered, limiting the plant's ability to access nutrients, but compaction directly influences the ease of air and water movement through soil.

Water retention is also disrupted, as compacted soil often has lower infiltration rates, leading to greater surface runoff rather than the absorption of water into the soil profile.

Overall, the decrease in soil aeration is critical because it affects both root health and nutrient availability, along with water movement in the soil, but it is the aeration aspect that is most directly tied to the consequences of compaction.