Regeneration of impaired biological soil properties caused by physical soil impact

Regeneration potential of impaired soil proper-ties is an important criterion for the assessment of impacts on soil quality. Physical impacts often result in anaerobic soil conditions that may lead to damages of biological soil properties. On construction sites, agricultural top-soil is routinely stored in stockpiles, where in depths of more than one meter often very low oxygen concentrations and elevated CO2 concentrations of up to 25% have been measured. In a laboratory experiment regeneration of biological properties of stockpiled soils was investigated. For this purpose soil samples were taken from different depth layers (0-20 cm, 80-100 cm and 180-200 cm) of two top-soil stockpiles that are five years old. The samples were incubated under aerobic conditions for 56 days. Microbial biomass, soil respiration, nitrification potential and structure of soil bacterial communities were determined before incubation and during the course of aerobic incubation. Before incubation the analyses revealed marked differences between the 3 depth layers. During the aerobic incubation soil microbial biomass did not change essentially, whereas regeneration of soil respiration and nitrification activity was nearly complete. Community structure of soil bacteria, determined as T-RFLP profiles of genes encoding the small subunit of the ribosomal RNA, showed distinct changes during incubation, but the differences among the depth layers remained throughout the incubation period. The data demonstrate clearly that different biological soil properties have a different regeneration potential and that this is important to define reliable parameters and criteria for assessing soil quality.