Valuing soil biodiversity
On an economic basis, soil biodiversity has both direct (the organisms themselves and/or their metabolic products) and indirect (the long-term outcome of their activities) uses. To try and put a value on biodiversity and soil biodiversity and describe what the natural environment does for mankind the term “ecosystem service” is used. These services are linked to soil function and a probable value placed on that function as well as a monetary value, biodiversity allows the function and stability of the soil to be regulated. Any perturbation may affect soil activity and any deleterious effects can be reduced if the functions of the soil are spread amongst different species. Otherwise removal of one keystone species or ecosystem engineer, may lead to catastrophic effects on the ecosystem. Similarly, the introduction of a keystone organism may also have catastrophic or beneficial effects, depending on the situation (Barros, 1999). This can be considered to be “ecological health” and results from the many components which make up the nutrient cycling or energy transfers. Because the function of soil system may be the key to understanding the health of agro ecosystems from an ecological perspective, soil biodiversity and soil health can also be seen as one measure of environmental quality.
Regardless of any ecological or monetary value, several authors (Hågvar, 1994; McNeely et al., 1995) have stressed ethical and moral reasons why biodiversity should be conserved. Most of the world’s religions give intrinsic worth to the natural world, and it is unlikely that this deep-seated notion will disappear, even despite the force of the economic use values placed on biodiversity. However, the world view that denies any sacred value or self-worth to nature is being rapidly spread throughout the world by globalization and modern industrial societies who view the world as a warehouse of commodities for human enjoyment. The danger of this to biodiversity conservation should not be underestimated, although the possibility of using biodiversity for enjoyment (e.g. ecotourism) and other benefits may serve to counteract the negative forces of ecologically ignorant consumer societies.
Protecting soil biodiversity
Protection of individual species has historically been the goal of conservation bodies and it has been relatively easy to define which species are under threat. For example the CITES Convention (Convention on International Trade in Endangered Species Flora) clearly defines which species should be protected. Recently, the focus has shifted away from individual species to conservation of habitats through the use of “keystone” species which act as indicator organisms within a particular environment or ecosystem. However, in cases where the habitat contains species which are unknown, unidentified or difficult to study a different approach needs to be adopted. In soil systems it is unlikely that we may ever know the true number and identify of all the species and it is virtually impossible to concentrate on a particular species because the same species may be found elsewhere (in an area not under threat) and they may interact more closely than in above ground habitats. In these cases, the strategy has been to focus on protecting the function of the ecosystem - so called “ecosystem services”. This allows a multi tiered approach to looking at soil which will embrace the different interaction levels which occur in soil. This complexity in soil, lack of knowledge and technical difficulties presents a unique challenge to conserving soil habitats.
In 2006 the European Commission adopted the Thematic Strategy for Soil Protection of European soils. The proposed Directive “lays down a framework for the protection and sustainable use of soil based on the principles of integration of soil issues into other policies, preservation of soil functions within the context of sustainable use, prevention of threats to soil and mitigation of their effects, as well as restoration of degraded soils to a level of functionality consistent at least with the current and approved future use of the land.”
The key elements of the Directive as proposed by the Commission are:
1. A requirement for central and local Government to consider the impacts that new policies will have on soils whilst they are being developed (Article 3);
2. A duty on all land-users to prevent or minimise harm to soils (Article 4);
3. A requirement to limit or mitigate the effects of soil sealing (the covering of the soil surface with an impermeable material such as concrete) (Article 5);
4. A requirement to reduce the risks relating to soil erosion, organic matter decline, compaction, salinisation, and landslides, by identifying risk areas, and deciding on a programme of measures to address these risks (Articles 6-8);
5. A requirement to prevent soil contamination, compile an inventory of contaminated sites and remediate those sites listed on the inventory (Articles 9-14); and
6. A requirement to raise awareness of soils issues, report to the Commission, and exchange information (Articles 15-17).
Action is required at EU level because:
· Soil is a non renewable natural resource of common interest to Europe because of the crucial functions it performs for society and the ecosystems.
· European environmental legislation is incomplete without soil policy, hampering the objective to reach a high level of environmental protection in Europe.
· Differences among Member States in dealing with soil problems may distort competition within the single market.
· Most of the costs of soil degradation are not borne by the land users, who are responsible for the degradation, but by the tax payers.
· Soil degradation has transboundary consequences.
· As soil contamination may affect the quality of food and feed products.
· The health of the European population can be impaired as a result of soil degradation.
Problems in conserving soil biodiversity
Many of the problems in conserving biodiversity are associated with the lack of recognition of the importance it plays in agricultural production. Although many farmers and the farming community have a profound knowledge of their agriculture, training and education is often needed to highlight the roles of the soil biota at various levels of the ecosystem/landscape. Soil quality assessments such as chemical and physical properties provide some knowledge of resources but should be supplemented with information on resources (human and organic such as composts) and biological indicators of soil quality and function.
To overcome any limitations to agricultural production, Swift (1999) proposed a series of potential “entry points” at which management practices could be improved. These include both direct interventions such as: inoculation for disease and pest control and soil fertility improvement (such as rhizobia, actinomycetes, mycorrhizae, diazotrophs) and indirect interventions through, for example, cropping system design, organic matter management and genetic control of soil function (manipulating resistance to disease, organic matter and root exudates). A potential set of improvements could be tested together using an “adaptive” experimentation approach whose results feedback over a number of cropping cycles. This would involve other members of the farming community such as extension agents and local community facilitators (TSBF, 2000) and be evaluated according to local agricultural, climatic, soil, socioeconomic and cultural conditions as long as the farmers etc can identify problems that may lead to the failure of the adopted system. Any system undertaken must be flexible to meet the needs and priorities of those concerned.
The final decision of whether to adopt the practice is by no means certain as the farmer may choose to revert back to the traditional management strategy. The selection of best practice is a long term process and requires a level of commitment, for example monitoring, and the appropriate incentives so that the improvements in agricultural production and human wellbeing can be shown and sustained.
Direct and indirect management practices with positive impacts on soil macrofauna
Direct management practices
Different studies suggest various options for conserving and stimulating the activities of soil macrofauna. For example, the negative effects of annual crops could be reduced by decreasing the intensity and frequency of perturbations such as tillage and the use of pesticides, and by increasing the quantity and quality of the energy resources used by the macroinvertebrates, e.g. the use of legume cover crops and the maintenance of crop residues. Integrated systems of short phases of crops with longer periods of pastures (3–5 years) are also an option for maintaining macroinvertebrate populations as well as bringing other benefits for soil physical and chemical parameters (Thomas et al., 1995).
Organic manuring helps to enrich or favour the multiplication of many soil fauna and microorganisms including those antagonistic to soil pests. In recent years, the application of greater quantities of synthetic fertilizers has been very common in contrast to the negligible use of organic manures. The eggs, larvae and pupae of soil insects are liable to be affected either by the soil-inhabiting pathogens or their toxins. However, the absence of organic manures in the soil
enables the above pests to thrive owing to the depletion of the natural biotic restricting factors. The increasing use of pesticides has also upset the balance of life in soil when they have been applied directly in the soil and by drip from the foliage. Their subsequent incorporation into soil can also reduce the natural enemies of soil insects.
Certain practices such us improved pasture can result in increased populations of soil macrofauna. The similarity of the original ecosystem and the derived agroecosystem tends to be a major determinant of native species’ survival, adaptation, resilience and stability within the boundaries of ecosystem management. The spatial arrangement of pastures alongside cropped plots can accelerate the recovery of macrofauna populations in the cropped plots. Beneficial species,
which can be more rapidly established, can also help reverse some of the degrading effects of cropping on soil structure, thereby avoiding the need to solve soil degradation problems with expensive, machinery-intensive strategies. Thus, earthworms become a resource that can be harnessed to improve ecosystem health (Jimenez and Thomas, 2001).
Indirect management practices
Where indirect management practices are used, interventions are a means of managing soil biotic processes by manipulating the factors that control biotic activity (habitat structure, microclimate, nutrients and energy resources) rather than the organisms themselves (Hendrix et al., 1990). Examples of indirect interventions include most agricultural practices, such as application of organic materials to soil, tillage, fertilization, irrigation, green manuring and liming as well as cropping system design and management.
In conventional agriculture, soil tillage is considered one of the most important operations for creating favourable soil structure, preparing the seedbed and controlling weeds. However, mechanical implements destroy the soil structure by reducing the aggregate size, and conventional tillage methods are a major cause of soil loss and desertification. In this kind of management system, the biomass produced is kept on the soil surface and serves as a physical protection of the soil and provides food for the soil fauna.
Pest management can also benefit from conservation practices that enhance biological activity and diversity, and hence competitors and predators as well as alternative sources of food. For example, most nematode species (especially pathogens) can be reduced significantly by the application of organic matter, which stimulates the action of several species of fungi that attack nematodes and their eggs. An agricultural technique used in a number of tropical countries in Africa, Asia and South America to ameliorate soil conditions for crops is “ecobuage. This is a complex agricultural system that entails incinerating herbaceous vegetation piled up in mounds and buried under a layer of soil taken from the surroundings. It is a traditional system that is more evolved than the slash-and-burn technique often used in intertropical zones. This system enables the cultivation of plants that are demanding in terms of nutrient supply. In addition, the earthworm activity improved soil porosity (macroporosity became more important), allowing plant roots to go deeper into the soil. Improved soil structure enabled the cropping of plants with tubercules that need an aerated soil for their development (Mboukou, 1997).