Indicators for Soil Quality Defining a framework to measure soil quality (Romanyà et ppt

From an anthropogenic point of view, soil quality may be then measured in terms of the services the soil provides to our society.. In this context, to our point of view, land management

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

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

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

4 Habitat for many organisms

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)

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