As the soil water content increases, the water film weakens these cohesive bonds and lubricates the particles, resulting in an increased potential for compaction. The detrimental effects of soil compaction on productivity are numerous but often indirect, making it easy to overlook or mistaken as a different production-limiting factor. Hammel explains that as soil is compacted, the number of large soil pores is reduced and soil density is increased. The resultant soil condition restricts the movement of water and air through the soil and increases the soil strength or resistance of the soil to penetration by roots. Physical resistance to root growth and an unfavorable root environment can lead to lower nutrient and water uptake, and consequently, severely stress the plant.
Compaction also reduces internal drainage which causes wet, poorly aerated soils.
Wet soils warm more slowly than well-drained soils, which can further reduce root growth rates. In addition, cool wet soils favor soilborne diseases such as Pythium root rot, Rhizoctonia root rot and takeall. Plants under stress are also much more susceptible to infection by root pathogens. Soil strength and pore size are the primary factors affecting root penetration. Crops grow best when the soil pore distribution and geometry matches the root size and configuration.