Table 20.1 illustrates a suggested minimun data set of indicator properties for the determination of soil quality in relation to the six functions descibed in Figure 20.1. For example, in the case of the nutrient-cycling function (that supports the plant productivity management goal), the soil quality indicators would include such measurable properties as potentially mineralizable nutrogen (PMN), soil test phosphorus level, soil pH, cation exchange capacity (CEC), and soil depth, among others.A particular management goal or ecological role involves several soil functions; each function may involve several processes; and each process may be associated with several biological, chemical, and physical indicator properties. Therefore, the number of properties measured to assess soil quality may be a dozen or more, many of which can be measure on-the-spot in the field (Plate 68). Each of these measurements must be interpreted with regard to its implications for the soil functions under consideration. For example, if the bulk density is measured as 1.5 Mg/m3, we must ask 'is this too high, too low, or just right?' to facilitate the functions of regulating water, providing habitat, and so on. For some indicators (e.g., soil organic matter) higher values may be more desirable, for others (e.g., bulk density) lower values are better, and for still others (e.g.,soil pH) there may be an optimum value, above or below which soil function suffers.