TYPES OF TILLAGE AS A PREREQUISITE FOR RETENTION OR ALTERATION OF PHYSICAL AND MECHANICAL PROPERTIES OF SOIL
The physical and mechanical properties of soil change dynamically following each tillage and rainfall. Some of the more important ones are bulk density, (g cm−3), hydraulic conductivity in soils, saturated with water, (cm day−1), the rainfall curve, the temperature (оС) and the capacities of soil to retain water at saturation point (cm3 cm−3). Theoretically, only the upper 30 cm of soil layer experience change in the physical and mechanical properties, caused by tillage. The actual depth of the changes in the soil depends on the production technology selected. Various types of tillage are applied worldwide, corresponding to the level of development of socio-economic formations and of the production technologies. In Bulgaria, the traditional annual ploughing of soil is applied, including on slopes, giving a prerequisite for the subsequent negative consequences, such as activation of erosion processes and degradation.