Various physical, chemical, and biological properties of soil interact in complex ways to determine its potential fitness or capability for sustained production of healthy, nutritious crops. The integration of growth-enhancing factors that make a soil productive has often been referred to as “soil quality”. The Soil Science Society of America (SSSA 1984) defines soil quality as an inherent attribute of a soil which is inferred from soil characteristic or indirect observations (e.g., compactability, erodibility, and fertility). Thus, soil quality has traditionally focused on, and has been equated with, soil productivity. More recently, the concept of soil quality has been broadened to include attributes of food safety and quality, human and animal health, and environmental quality (parr et al. 1992). In view of this, soil quality might be defined as:
“The capacity or capability of a soil to produce safe and nutritious crops in a sustained manner over a long-term, and to enhance human and animal health, without impairing the natural resource base or adversely affecting the environment”.
Although not well understood, soil quality may also play a major role in plant health and in the nutritional quality of the food that is produced. Thus, if properly characterized, soil quality should serve as a measure or indicator of changes in (a) the soil’s capacity to produce optimum levels of safe and nutritious food, and (b) its structural and biological integrity, which can relate to the status of the certain degradative processes, as well as environmental and biological plant stresses.
Thus, soil quality is directly related to the state of soil degradation which can also be defined as the time rate of change in soil quality (parr et al. 1992). The maintenance or restoration of soil quality is highly dependent on organic matter and an array of beneficial macroorganisms and microorganisms that it supports. The proper and regular addition of organic amendments such as animal manures and crop residues can effectively offset many of these degradative processes. It is also the best and most expedient means of developing a biologically-active soil that requires little energy for producing crops; increases the resistance of plants to pests and diseases; and enhance the decomposition of toxic substances such as residual pesticides (Sampson 1981; hornick and parr 1987; parr et al. 1992).