Soil quality can be broadly defined as the sustained capability of a soil to accept, store, and recycle water, nutrients and energy. Measures of different properties (key indicators) of soil quality are required to explore better the concept of “resilience” which can be defined as the ability of a degraded ecosystem to revert to its original or near original performance (status) that existed before the external forces altered its natural equilibrium. It is universally accepted that the main causes of soil degradation are the biological impoverishment and loss of organic matter due to overgrazing, intensive use, climate changes, pollution and heavy fertilization and irrigation with salt waters. An extreme degradation of soil physical and biological resources, leads to an irreversible decline of soil functionality and hence, to the beginning of a desertification process. The aim of this research is to deepen the understanding of the processes that best represent the most significant aspects of soil "quality" in different environmental situations. The selection and use of reliable tools and techniques to contrast the degradation processes taking place in soil by improving its quality and its ecological function have been also studied.
Our research group is continuing to study the level of biological and chemico-physical degradation of the soils in order to assess the soil resistance to different impacts and/or the resilience of degraded soils under rehabilitation practices. Due to the complexity of processes and mechanisms characterizing soil ecosystems, different parameters are needed to evaluate soil quality and degradation. These parameters have to include chemical, physical, and biological properties of the soils. In particular, chemical (organic matter content, fractions of organic carbon, concentration of nitrogen both on total and soluble forms, mineral nutrients concentrations, etc.), physical (permeability, aggregate stability, soil structure), and biological (soil biodiversity, respiration, enzyme activities, etc.) parameters are determined to better understand soil bio-physical processes which sustain the soil resource.
In Fig. 1 results about a study on the effects of some bioremediation treatments of a polluted soil have been reported. Specific biochemical parameters (b-glucosidase and phosphatase activities, enzymes related to C and P cycles), which take place in the soil decontamination, showed increased values over the time in the treatments with compost (C and CL). The greater availability of substrates and the reduction of contaminants, which could have an inhibitory effect on the activity of hydrolytic enzymes, were probably the reason this trend.