It poses a very serious threat to good soil structure. Delicate soil pores are easily crushed, decreasing their capacity for water and air movement and hindering root growth. Wet soil is particularly vulnerable, because water lubricates soil particles and loosens binding agents. Small particles slip between the larger particles, filling the pore spaces. Loose soils will compact more than tight soils, and soils that have a broad range of particle sizes can be more severely compacted than more uniform soils.
Few soils can withstand traffic without becoming severely compacted.
Compaction depends not only on the amount of pressure exerted, but also on the duration and frequency of exertion. Pressure spreads with depth, so the compacting effects of pedestrians and vehicles usually occur to the top four inches of the soil. Compaction is easier to prevent than to remedy. Avoid cultivating wet soils. Keep foot and vehicle traffic over the roots to a minimum.