Changing the nature of the soil such that there is a decrease in the volume of voids between soil particles or aggregates; it is manifested as an increase in bulk density and a severely compacted soil can become significantly less permeable and less aerated. Manmade compaction is caused by poaching (trampling of animal hooves repeatedly) or by the passage of heavy machinery. Other typical examples are “plough pans” (plough sole or traffic pan) which can be formed due to tillage and which can negatively affect root development and drainage.