As one of the vital natural resources, soil plays an important role in producing food and fiber for human beings, maintaining the terrestrial ecosystems and serving as a medium for plant growth, a sink for heat, water, and chemicals, a filter for water, and a biological medium for the decomposition of wastes. By interacting intimately with water, air, and plants, soil can buffer environmental fluctuations and regulate many ecological processes that control water and air quality and promote plant growth.The concept of soil quality defined as the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality and support human health and habitation. It was introduced to facilitate soil research by understanding soils more completely and by assisting the decision-making in the use and allocation of labor, energy, fiscal, and other inputs during the procedure of agricultural production. Consequently, soil quality provides a useful and universal concept for educating professionals, producers, and the public about the importance of soils. It also can be used to assess the impacts of management practices and land uses on soils.
Basically, soil quality is comprised of soil physical, chemical, and biological properties. So it is necessary to develop soil quality indicators which describe soil functions in natural and agro-ecosystems: promoting plant growth, protecting watersheds by partitioning and regulating precipitation and preventing air and water pollution. Monitoring the changes in soil quality indicators can provide useful information on the dynamics and trends of soil quality. Many soil attributes could serve as indicators of soil quality. However, they are often highly correlated, making it difficult interpret the significance of changes in selected soil quality indicators. And also the scale problem should be taken into account. Indicators can be adjusted to match the scale of assessment or can be expanded to larger scales using various statistical procedures. A minimum data set (MDS) consisting of a set of soil attributes including soil chemical, physical and biological properties are selected to assess soil quality. The fitness of indicators used for soil quality assessment varies spatially depending on land types or land use, soil function and soil forming factors. Different land-use types may require adjusted critical limits and target values of certain soil functions, and require certain additional indicators for specific assessment. Various approaches, such as multiple-variable indicator kring (MVIK) method, integrated scoring method, dynamics method, and relative quality method, have been used to assess soil quality.
Ecologically incompatible human land-use and management practices such as deforestation and soil fertility depletion, cultivation, and land conversion, have greatly altered the global biogeochemical cycles and the dynamics of soil characteristics. Worldwide concern about soil degradation has been given, since it greatly threatened the soil resources on which humans live. Based on the discussion of basic concepts, we synthesized the research advances in the impact of land use changes on soil physical, chemical and biological quality. The problems needed to be solved in soil quality research and key issues for future studies were then analyzed. Much attention should be paid on soil quality indicator and assessment method, mechanism of soil quality change, scaling issue, and the practices of soil quality maintenance in the future studies.