Soil management effects on biological indicators of soil quality

Abstract

Soil biological indicators provide insight into the living component of the soil. Similar to physical and chemical indicators, biological indicators have a relationship to soil functions and can evaluate soil functions to assess soil quality. These indicators are dynamic soil properties that are very sensitive to land management, natural disturbances, and chemical contaminants. Doran and Safley (1997) and Pankhurst et al. (1997) suggested that an indicator, regardless of its nature, must fulfill the following criteria: (1) be interpretable; (2) correlate well with ecosystem processes; (3) integrate soil physical, chemical, and biological properties and processes;(4) be accessible to many users; and (5) be sensitive to changes. In addition, an indicator must have reproducibility, low temporal and spatial variability, and simple sampling and analytical methods. It is important to understand which indicators to test, what information is needed for the appropriate management of a soil, and where to get this information. In general, biological indicators that tell us about soil processes mediated by soil organisms are the most informative about soil function. There are myriads of organisms in the thin layer of the soil surface. They play key roles in the decomposition of soil organic matter, nutrient cycling, soil pollutant degradation, and the formation and stability of soil structure. They adapt to changes in their environment, such as stress due to drought, flooding, substrate shortages (e.g., food shortages), and contaminants. Soil biota also respond rapidly to soil management and land use changes and can be candidates for soil quality indicators. There are, however, limitations in directly measuring soil organisms as indicators of soil quality. Because of this, biological dynamic properties (respiration, POM, PMN, and enzymes) are often selected as surrogates for measurement of processes mediated by soil biota. Phospholipid fatty acids and DNA are also gaining popularity in academic and research laboratories. Soil respiration is measured at the field and in field office. Earthworms, which are not often diverse and are easy to count, are the only biota that have been considered usable as biological indicators by personnel regardless of special training and that are presently measured in the field by determination of their abundance. Biological indicators may reflect the overall number, type, and activity of microorganisms and the diversity of the living organisms in soil, particularly the microbial population. Some biological indicators are linked to the organic matter fractions (POM, β-glucosidase), nitrogen pools (PMN), or soil biota (respiration).