Soil quality: the foundation of a sustainable agriculture

The various chemical, physical, and biological properties of a soil interact in complex ways that determine its potential fitness or capacity to produce healthy and nutritious food. The integration of these properties and the resulting level of productivity is referred to as "soil quality". Soil quality can be defined as an inherent attribute of a soil that is inferred from its specific characteristics and observations (e,g., compactability, erodibility, and fertility). The term also refers to the soil's structural integrity which imparts resistance to erosion, and to the loss of plant nutrients and soil organic matter, Soil quality is often adversely affected by soil degradative processes such as soil erosion, salinization, and desertification. Indeed, soil degradation can be defined as the time rate of change in soil quality. There is a growing consensus that the concept of soil quality should not be limited to soil productivity, but should be extended to include the attributes of environmental quality, human and animal health, and food safety and quality. In attempting to characterize soil quality, chemical and physical properties have received much greater emphasis than biological properties because their effects are easier to measure, predict and quantity. In fact, our knowledge of how soil microorganisms affect food quality, environmental quality and human and animal health is rather limited. Future research should seek to identify, and quantify reliable and meaningful biological ecological indicators of soil quality, including total species diversity, or genetic diversity of beneficial soil microorganisms. We need to know how these indicators are affected by management inputs, and how they relate to the sustainability of agricultural systems.