The soil quality concept and the development of organic farming

By Per Schjønning, Susanne Elmholt and Bent T. Christensen, Danish Institute of Agricultural Sciences

Organic farming is based on a sustained quality of the soil resource. The term ‘Soil Quality’ is hence used very often in scientific papers and discussions on organic farming issues. However, like the term ’sustainability’ it has become a ’buzz’ word with no clear meaning, and there is an urgent need to analyse and define the term more precisely. Most frequently, it is used to describe soil attributes. However, soil quality should be regarded as a concept and not just as a common denominator for specific soil attributes. This is one key conclusion drawn in a new book entitled ‘Managing Soil Quality: Challenges in Modern Agriculture’ (Schjønning et al., 2004; CABI Publishing).

The book includes a chapter dealing with organic farming as a system. However, the main focus is on basic sustainability considerations when evaluating the soil and the effects of different management. Therefore, we see this book as a valuable contribution to the on-going development of sustainable practices in organic farming. In the following, the book shall be briefly introduced. The full text of the introductory chapter ‘Managing Soil Quality – Concepts and Terms’ is available from Organic Eprints.

Soil quality as a concept

Soil quality is how well soil does what we want it to do. This statement, extracted from the web-site of the USDA Soil Quality Institute, represents the very essence of the soil quality concept. The statement includes two aspects: ‘how well’ relates to grading soils while ‘what we want’ relates to priority of soil functions. Most previous books on soil quality have emphasized the descriptive grading of soils or management effects, often by focusing on soil quality indicators, i.e. specific soil attributes. It seems more relevant, however, to focus on the soil quality concept as it relates to what we want the soil to do. Clearly, we must define what we want before considering how well this service is delivered.

Science is a human activity, and science and society interact. As a result of this, the focus of science will inevitably reflect the priorities of society as exemplified in our book. Societies with shortage of food supply focus on soil productivity, while societies with abundant supply of affordable food switch their focus from sheer productivity to the overall sustainability of the food production systems. Sustainable agriculture involves a sustained productivity but also the protection of natural resources. The concept of soil quality is deeply rooted in considerations on sustainable production, but since the priorities of society change over time and differ from one society to another, soil quality cannot be aligned with the universal laws of nature. In other words, the concept of soil quality is a human construct allowing specific soil functions to be evaluated against specific purposes. Nevertheless, the soil quality concept has so far been used mainly as a technical framework for grading soil and evaluating management effects. This approach is difficult across soil types, climates and cropping systems. In our opinion, more emphasis should be put on soil quality as a cognitive concept closely associated with sustainability.

Soil quality and soil fertility

The term 'soil quality' should not be confounded with the term 'soil fertility' (Patzel et al., 2000). Soil fertility primarily relates to the soil's productivity. In contrast, soil quality is a more basic term including the soil's ability to fulfil all potential uses and functions of soil. An important part, of course, is the soil productivity or soil fertility. However, sustainable farming also has to consider impacts on the environment and other concerns. The soil quality term thus most often includes three concerns as shown in Figure 1.

Major challenges in modern agriculture

In the book, we have asked a number of internationally well known researchers, all experts within their field, to address specific challenges and key issues in modern agriculture. Accordingly, most contributions relate to challenges facing industrialized countries. However, the book also includes an important chapter devoted to soil quality in developing countries. Each contributor was asked to discuss his/her area with respect to the soil quality concept outlined above. This involved the potential identification of threshold values of soil quality indicators that the author(s) judged sustainable. And further the potential identification of what management is needed (management threshold) to produce the desired soil quality. For these exercises we adapted the definition of soil quality suggested by the Soil Science Society of America: Soil quality is 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. Each author was encouraged to define the sustainability criteria on which they based their discussion of good and bad soil quality.

The challenges addressed in our new book include major plant nutrients (N, P, K), soil acidity, soil organic matter, soil biodiversity, soil compaction, erosion, pesticides and urban waste. Not surprisingly, it turned out that most issues are highly complex and that it is extremely difficult – some authors think impossible - to identify simple thresholds for both soil quality indicators and management. Much effort went into identifying indicator levels or management thresholds for all topics discussed. However, simple answers could not be given in general. For example, the authors dealing with soil biodiversity stated that a causal relationship between soil biodiversity (a potential soil quality indicator) and ecosystem functioning and stability does not seem to exist. One difficulty in establishing management thresholds is soil type differences. In our synthesis, we discuss the contributors’ conclusions in relation to a suggested ’minimum data set’ (Larson & Pierce, 1991) and indices that seek to integrate a number of soil attributes into one number expressing the ’soil quality’ (e.g. Andrews et al., 2002). From the lessons learned during the editing work on this book, we would clearly dissuade such approaches.

Research and the communication of knowledge

Although the conclusions above may seem discouraging, the concept of soil quality remains useful as a tool of expressing sustainability considerations. Rather than hiding details in indexed expressions of soil quality, the researcher should relate a measured soil attribute to a specific purpose. The researcher is thus faced with the challenge of transferring scientific results to the end-user without reducing the complexity of the issue. This further calls for well-educated farmers, extension officers and decision makers in general. Each particular type of soil has a characteristic ’window of opportunity’ as a function of management, a term suggested by Bouma (1994) as a tool for scientists and decision makers cooperating on land-use problems. We support Bouma’s suggestions that scientists should participate in ’research chains’ implying methodical steps in a process of identifying, selecting, resolving and presenting the soil quality issue and the knowledge gained. This ’chain’ approach should be performed by interdisciplinary groups of researchers and stakeholders for identifying the limits of the ’window of opportunity’ as a relevant measure of soil quality for any given type of soil.

Quantification of sustainability – an example

According to Smyth and Dumanski (1993) and as later promoted by Bouma et al. (1998), sustainable management of agricultural land should simultaneously (i) maintain or enhance production and services, (ii) reduce the level of production risk, (iii) protect the potential of natural resources and prevent degradation of soil and water quality, (iv) be economically viable, and (v) be socially acceptable. These priorities are quite in line with the fundamental rules for organic farming. Below, we exemplify how these concerns are addressed in our book. Askegaard et al. (2004) note that potassium (K) reserves are easily accessible and long-lasting, and that K lost from agriculture represents no threat to the environment (part of criteria (iii) above). Further, there appears to be no potential health hazards from a balanced use of K (criteria (ii) above). Nevertheless, crop production under reduced K input is a key issue in their presentation. They recall the suggestions made by the Brundtland Commission (WCED, 1987) and base their contribution on the initial part of the criteria (iii) that agricultural management should protect the potential of the natural resources, thereby demonstrating an awareness of the criteria (v) on ’acceptability’. Their efforts concerned with sustained productivity in low K input systems probably reflect the general increase in organic farming, which avoids the use of mined fertilizers. This way, the authors incorporate the sustainability criteria (i) and (iv) above. The further development of organic farming requires an open discussion of all sustainability concerns, including costs and benefits in meeting each of them.

Emergent property or specific management effect

Emergent properties are defined in the book as functional interactions of system components that cannot be observed in studies of smaller units of organization (Carter et al., 2004). Such system properties are often highlighted as key aspects of organic farming when viewed in a holistic perspective. However, in their discussion of two different systems (conservation tillage and organic farming), Carter et al. realize that farming practices fall along a continuum – and often with some overlap – rather than into discrete groups. This is an important recognition when attempting to compare systems. Emergent properties are important in studies on effects of soil management, but a system characteristic should not be considered as an emergent property if it is in reality caused by a specific management tool. Analysing and developing agricultural systems may thus be more relevant than comparing a given system with a ‘conventional’ system (Lockeretz, 1987; Raupp, 1993; Schjønning et al., 2002).

Perspectives

There is an urgent need for more interaction between descriptive and prescriptive branches of science. Typically, scientists in specific scientific disciplines perceive soil as an ecosystem component, and their approach is descriptive and observational in nature. Agricultural researchers, on the other hand, are concerned primarily with the production of food, feed and fibre, and perceive soils mainly as media to support plant growth. Thus, researchers involved in agricultural sciences are accustomed to produce prescriptions with the clear aim of increasing yields. We advocate a combination of the conceptual/descriptive and the quantitative/prescriptive approaches.

Much research is dealing with the processes of soil degradation (e.g. water erosion). We need a more management oriented approach in order to identify ways (prescriptions) of reducing or avoiding soil degradation. In this context, the precautionary principle shall probably become increasingly more important in the interaction with stakeholders in the society. The precautionary principle is a culturally framed concept that takes its cue from changing social conceptions about the appropriate roles of science (O’Riordan and Cameron, 1994). The concept is related and interacts with the sustainability concept. One basic issue of the precautionary principle is thoughtful action in advance of scientific proof, which is rather difficult to combine with science. It means that management decisions should be based on a ‘burden of evidence’ when ‘hard’ data are not available (O’Riordan et al., 2001). However, we anticipate that this principle shall increasingly face and provoke scientists, because concerned citizens, non-governmental organizations and political movements become more and more important in setting the research agenda in society. Considerations on precautionary actions shall inevitably appear on the agenda of teams dealing with land management, where any decision has to be based on evaluations of benefits, risks and costs. Hence there shall be an increased demand for scientists to deliver data including the probabilities of occurrence rather than fixed (mean) values. The scientific community should face this inevitable challenge by explicitly considering the sustainability concept and on this background interact with stakeholders in scientifically founded implementation of the precautionary principle. The contributions to the new book ‘Managing Soil Quality: Challenges in Modern Agriculture’ may serve as part of the basis on which this implementation can take place.

References

Andrews, S.S., Karlen, D.L. and Mitchell, J.P. (2002) A comparison of soil quality indexing methods for vegetable production systems in northern California. Agriculture Ecosystems and Environment 90, 25-45.

Askegaard, M., Eriksen, J. & Johnston, A.E. (2004). Sustainable Management of Potassium. In: Schjønning, P., Elmholt, S. & Christensen, B.T. (eds.) (2004) Managing Soil Quality: Challenges in Modern Agriculture. CABI Publishing, Wallingford, UK, pp 85-102 (in press).

Bouma, J. (1994) Sustainable land use as a future focus for pedology. Soil Science Society of America Journal 58, 645-646.

Bouma, J., Finke, P.A., Hoosbeek, M.R. and Breeuwsma, A. (1998) Soil and water quality at different scales: concepts, challenges, conclusions and recommendations. Nutrient Cycling in Agroecosystems 50, 5-11.

Carter, M.R., Andrews, S.S. & Drinkwater, L.E. (2004) Systems Approaches for Improving Soil Quality. In: Schjønning, P., Elmholt, S. & Christensen, B.T. (eds.) (2004) Managing Soil Quality: Challenges in Modern Agriculture. CABI Publishing, Wallingford, UK, pp 261-281 (in press).

Larson, W.E. and Pierce, F.J. (1991) Conservation and enhancement of soil quality. In: Evaluation for Sustainable Land Management in the Developing World. Int. Board for Soil Res. and Management, Bangkok, Thailand, pp. 175-203.

Lockeretz, W. (1987) Establishing the proper role for on-farm research. American Journal of Alternative Agriculture 2, 132-136.

O’Riordan, T. and Cameron, J. (eds.) (1994) Interpreting the Precautionary Principle. Cameron May Ltd., London, UK.

O’Riordan, T., Cameron, J. and Jordan, A. (eds.) (2001) Reinterpreting the Precautionary Principle. Cameron May Ltd., London, UK.

Patzel, N. Sticher, H. and Karlen, D.L. (2000) Soil fertility - phenomenon and concept. Journal of Plant Nutrition and Soil Science 163, 129-142.

Raupp, J. (1993) Einige Gedanken und Leitlinien zur Forschung im ökologischen Landbau. Ökologie und Landbau 21, 9-12.

Schjønning, P., Elmholt, S. & Christensen, B.T. (eds.) (2004) Managing Soil Quality: Challenges in Modern Agriculture. CABI Publishing, Wallingford, UK, 368 pp (on sale from December 2003).

Schjønning, P., Elmholt, S., Munkholm, L.J. and Debosz, K. (2002) Soil quality aspects of humid sandy loams as influenced by organic and conventional long-term management. Agriculture, Ecosystems and Environment 88, 195-214.

Smyth, A.J. and Dumanski, J. (1993) FESLM: An international framework for evaluating sustainable land management. World Resources Reports 73. Land and Water Development Division, FAO, Rome, 77 pp.

WCED (1987) Our common future: The Brundtland report. Report from the World Commission on Environment and Development (WCED). Oxford University Press, Oxford.