Contact your county Extension agent or land grant university for more specific information on soil compaction. Soil pores may be reduced in size or eliminated altogether, usually due to pressure applied to the soil surface by equipment, foot traffic, or hard rain on bare soil.
Wet soil is especially vulnerable to compaction.
It's always wise to keep all traffic off of wet soils. Without enough sizable pores, plant roots find it difficult or impossible to grow and penetrate into new soil. Air, water, fertilizers and pesticides fail to infiltrate through surface crusts or plowpan layers in compacted soils, robbing the roots of essential nutrients, water and oxygen. Plants are starved because roots are not able to function to capacity. Drought symptoms may appear, even with plenty of rain, watering, or standing water on the soil surface because water cannot get through the soil to the roots.