1.1.1. Soil compaction
This soil degradation can be defined as a process of unfavorable increase in the bulk density of the soil accompanied by a decrease in its porosity and water permeability. Possible reasons for soil compaction are: wet soil cultivation, excessive traffic, use of heavy agricultural machinery, re-plowing at the same depth, trampling by passing animals, poor soil structure, and low organic matter content.
Various indicators can be used to assess soil compaction, such as soil bulk density, penetration resistance, porosity, root depth distribution. Among them, the bulk density is the most easily feasible and complex. Kercheva and Dilkova (2005) offer reference optimal, critical and limit values for bulk density, taking into account soil aeration, soil texture and content of SOM (soil organic matter). Limit values for bulk densities of 1,85, 1,6 and 1,35 g / cm3 are determined for soils with coarse, medium and clay texture of horizon A or the arable soil horizon, respectively. Volume density values of 1.7-1.8 g / cm3 are typical for a plow heel. Unacceptably high values of bulk density can be obtained by repeatedly passing machines on the soil surface when fertilizers, pesticides or other treatments are applied, especially when the soil is moist.