4. Indicators for Soil Quality Defining a framework to measure soil quality (Romanyà et al.) Romanyà J 1 , Serrasolses I 2 & Vallejo R.V. 1,2 1 Universitat de Barcelona 2 CEAM. Centro de Estudios Ambientales del Mediterráneo. Soil provides a list of services to all users of terrestrial ecosystems and is crucial to our agricultural societies. From an anthropogenic point of view, soil quality may be then measured in terms of the services the soil provides to our society. The value of soil services to human societies has changed during history and thus the value we give to soils has also changed over time as it depends upon the economic and cultural basis of a society for a given context. While throughout history human awareness of the soil services has been mainly reduced to food, fibre and bioenergy production, nowadays the list of soil services has largely increased (see Table 1) and we are beginning to realise that soil management is no longer a local but a global issue affecting not only food and goods supplies but also to the human welfare and health. In other words, this societal awareness of the multiple functions of soils is not limited to an specific land use but to the whole landscape. Over the last century, as a result of the world increasing population and soil products demand, soil use has been intensified throughout the world and have promoted great scale changes in land use (agricultural land abandonment and urban sealing in good lands in developed countries and deforestation in developing countries). In developed countries increased forest land has been allocated to protect the environmental quality (e.g. water catchments, biodiversity conservation, C sequestration). However, forest soils in developed countries occupy less or much less than a 40 % of the land, and suffer a dramatic reduction in the developing countries. In consequence, some authors have recently stated that the protection of environmental quality and human health should be extensive to all land uses including productive land as well (see Foley et al., 2005). In this context, to our point of view, land management and planning should consider the ability of soils to function under different land uses, the reversibility of any land use change and the multifunctionality of soils (productivity, environment and human health). In consequence, the evaluation of soil quality should address holistically the following three principles across all soil uses: 1. Food security (quality and quantity) 2. Environmental quality and biodiversity 3. Human health and welfare Although none of these principles is solely dependant on soils they are all very much related to soil functioning. Soil quality assessment Soil quality assessment typically includes the quantification of indicators that are often derived from reductionist studies or general qualitative observations of the soil (Seybold et al., 1998). Overall, soil quality indicators condense the enormous complexity of the soil (Schjonning et al. 2004) in an attempt to describe the capacity of the soil to function. In spite soil quality indicators will not give a complete picture of the soil system we think they should attempt to cover, as much as possible, all soil functions relevant to human life although the relative weight of each one may change according to the land use and/or the environmental context. Thus, soil quality indicators should address the most relevant threats to soils in a given context and should be referred to their respective soil degradation thresholds. Soil degradation thresholds are specific to soil type and environmental conditions and should also cover all soil functions. In figure 1 we depict a framework for the establishment of soil quality indicators. Within this frame we first define the general soil degradation thresholds and then at the local scale we also need to address the specificity of the land management impacts, and define the threats associated to a specific soil management. To do so we consider the management thresholds. According to Schjonning et al. (2004) management thresholds can be defined as the most severe disturbance any management may accomplish without inducing significant changes towards unsustainable conditions. These management thresholds must consider the soil type and environmental context that define the soil degradation context, may be specific to the soil use and management context, and may thus stress one of the general soil functions but not forget about the rest. In table 2 we present a list of selected indicators that are often used for assessing soil quality. In general these soil indicators are mainly related to soil productivity and only address the old threats to soils (erosion, salinisation, loss of organic matter, compaction …). These soil quality indicators hardly address the processes associated to the new threats to soil such as contamination. Soil contamination is a highly complex issue to cope with chiefly when we consider the multi-functionality of soils. Monitoring soil contamination can be addressed by risk analysis however, this type of analysis is not a straightforward methodology to be applied to soils as it includes toxicology studies for organisms (including humans) living in other environmental compartments. Under these circumstances, a conservative record list of soil inputs for traceability purposes should help assessing soil contamination issues. We think thus, that when assessing soil contamination issues we should consider that the soil quality indices monitoring the intrinsic soil function are not going to be comprehensive for many of the soil contamination processes as they do not account for the effects of the pollutants transferred to other environmental compartments. References Foley J.A., DeFries R., Asner D.F., Barford C., Bonan G., Carpenter S.R., Chapin F.S., Coe M.T., Daily G.C., Gibss H.K., Helkowsky J.H., Holloway T., Howard E.A., Kucharik C.J., Monfreda C., Patz J.A., Prentice C., Ramankutty N. and Snyder P.K. 2005. Global consequences of land use. Science. 570-574. Karlen D.L., Mausbach M.J., Doran J.W., Cline R.G., Harris R.F. and Schuman G.E. 1997. Soil quality: a concept, definiton, and framework for evaluation. Soil Science Society of America Journal 61: 4- 10. Schjonning P., Elmholt S. and Christensen B.T. 2004. Soil quality management. Concepts and terms. In: Schjonning P., Elmholt S. and Christensen B.T. (eds.). Challenges in modern agriculture. CAB International. pp 1-15. Seybold C.A., Mausbach M.J., Karlen D.J. and Rogers H.H. 1998. Quantification of soil quality. In: Lal R., Kimble J.M., Follet R.F. and Stewart B.A. (eds.). Advances in Soil Science CRC Press. Boca Raton. Florida pp. 387-404. Table 1. List of main soil services. Soil services to human society Major concerns 1. The base for terrestrial primary production (agriculture and forestry) Productivity 2. Regional climate and air quality regulation (carbon sequestration) Environment 3. Regulation of water quality and supply Environment 4. Habitat for many organisms (biodiversity) Environment 5. Natural system to recycle organic matter and nutrients and to prevent pathogen dispersion (purifying capacity) Environment & Human Health Table 2. Selected indicators of soil quality and some processes they impact (adapted from Karlen et al., 1997). Measurement Process affected Organic matter Nutrient cycling, pesticide and water retention, soil structure Infiltration Runoff and leaching potential, plant water use efficiency, erosion potential Aggregation Soil structure, erosion resistance, crop emergence, infiltration pH Nutrient availability, pesticide absorption and mobility Microbial biomass Biological activity, nutrient cycling, capacity to degrade pesticides Forms of N Availability to crops, leaching potential, mineralisation and immobilisation rates Bulk density Plant root penetration, water- and air-filled pore space, biological activity Topsoil depth Rooting volume for crop production, water and nutrient availability Conductivity or salinity Water infiltration, crop growth, soil structure Available nutrients Capacity to support crop growth, environmental hazard Soil surface Erosion, crusting, sealing, infiltration Figure 1. Framework for establishing soil quality indicators. . 4. Indicators for Soil Quality Defining a framework to measure soil quality (Romanyà et al.) Romanyà J 1 , Serrasolses I 2 & Vallejo R.V. 1,2 1 Universitat de Barcelona 2 CEAM not forget about the rest. In table 2 we present a list of selected indicators that are often used for assessing soil quality. In general these soil indicators are mainly related to soil. the land management impacts, and define the threats associated to a specific soil management. To do so we consider the management thresholds. According to Schjonning et al. (2004) management