Chapter 3. Workshop discussions and findings on improving understanding and management of soil biodiversity and ecosystems for productive and sustainable agriculture

Soil biodiversity understanding, status and trends

Biological indicators of soil health

The workshop participants agreed on the need for technical assessments to advise farmers, policy-makers and planners on indicators and methods for the assessment and monitoring of soil health and functions. These should focus on improving knowledge: on the roles and importance of diverse soil organisms in providing key goods and services; and on the positive and negative impacts of existing and new agricultural technologies and management practices.

In order to facilitate comparison at many scales, it is important to agree on and adopt standardized approaches to the use of soil health indicators. Currently, standard methodology is used for most bioindicator measurements (e.g. microbial biomass) but sampling strategies may vary (e.g. depth of soil used for sample collection). Basic requirements for the development of specific bioindicators would be:

• relevance to basic attributes of soil function;


• response to management in acceptable timeframes;


• ease of assessment or measurement;


• robust methodology with standardized sampling techniques;


• cost-effectiveness;


• compatibility with physical and chemical indicators of soil health.

Soil biotic systems are extremely complex, and assessment of soil health and ecosystem function by direct measurement of overall biodiversity is impractical. Therefore, the need to develop indirect assessment methods is compelling. In order to be practical for use by practitioners, extension workers, scientists and policy-makers, the set of basic soil health indicators should be applicable over a range of ecological and socio-economic situations.

Appropriate use of soil health indicators will depend to a large extent on how well these indicators are understood with respect to the ecosystem of which they are part. Tools and methodologies to measure soil health should be adapted to end users (Table 2). Tests should be able to measure properties of soil health that are meaningful to the actor’s understanding of soil and its process, and to give results that are reliable, accurate within an acceptable range, and easily understood and used.

Soil organism and biotic parameters, such as abundance, diversity, food web structure, and community stability, meet most of the criteria for useful indicators of soil quality. They respond sensitively to land management practices and climate. In addition, they correlate well with beneficial soil functions, including water storage, decomposition and nutrient cycling, detoxification of toxicants, and suppression of noxious organisms. Visible indicators such as earthworms (Plate 4), biogenic structures, e.g. termite mounds (Plate 5), insects and moulds are comprehensible and useful to farmers and other land managers, who are the ultimate stewards of soil quality. Several farmer-participatory programmes for managing soil quality have incorporated abiotic and simple biotic indicators.

PLATE 4. An endo-anecic earthworm from the Colombian savannahs, Carimagua - [J.J. Jiménez]

The activities of soil organisms interact in a complex food web with some subsisting on living plants and animals (herbivores and predators), others on dead plant debris (detritivores), on fungi or on bacteria, and others living off but not consuming their hosts (parasites). One of the major difficulties in the use of soil organisms per se, or of soil processes mediated by soil organisms as indicators of soil health has been methodological, i.e. what to measure and how, when to measure it, and how to interpret changes in terms of soil function.

Table 2, prepared by workshop participants, summarizes the characteristics of potential soil health indicators required at different levels. It presents examples that end users can select and use in order to provide a suitable set of indicators of soil health according to local monitoring capacities. There is also a need to ensure that they are relevant to the given region, farming system, soil type, climate, etc.

Development of an assessment and monitoring framework

The identification of appropriate indicators of soil health assessment is complicated by the fact that they must account both for multiple dimensions of soil functions, such as productivity and environmental well-being, and the multiple physical, chemical and biological factors that control biogeochemical process, and their variation over time and space.

Plate 5. Termite mound from Africa - [C. Rouland]

All of the soil parameters typically need to be measured simultaneously at a field site, although there can be gaps in the data if some analyses are not feasible or the facilities are not available. The database is most useful where the soil properties are analysed in conjunction with one another. Thus, it is more useful to have data on all soil properties at a single point, than to have separate databases of generalized properties.

Table 2. Practical tools for measuring soil health and their basic characteristics

Figure 2. Pyramid of soil health indicators

Figure 2 presents the suite of soil health assessments in the form of a pyramid, with three sides corresponding to biological, chemical and physical indicators. The top of the pyramid represents the group of simple indicators that farmers would use, linked to the more complex indicators higher up the pyramid (e.g. total C) will be more useful for stakeholders who require soil health information at more detailed scales.measures lower in the pyramid. The more technical indicators occur in the lower part, but may move up as protocols are simplified or surrogate indicators are developed. There is a decrease in spatial resolution and scale with increasing complexity of the indicators. Therefore, simple

Development of target values and thresholds

Soil biota are among the most diverse communities in the world. Soil organisms regulate a number of processes in terrestrial ecosystems that are critical for productivity and essential for maintaining ecosystem health. The loss of any biodiversity from the natural ecosystem levels should be regarded as detrimental. However, food security requires some degree of compromise even where sustainable practices are employed. Therefore, the potential for adopting target and threshold levels of biodiversity needs exploration. Data and information required for sustainability assessment are generally unavailable, sparse or incomplete. The continued development of nationally and internationally agreed methods of soil quality assessment is a priority. The group confirmed that, in view of the limited information currently available on sustainable levels of soil biodiversity, a major scientific and socio-economic research programme is justified. As illustrated in Figure 3 (prepared by the working group), determination of the direction and rate of trends would be important, and identification of those indicators that respond more rapidly than others (e.g. microbial or macrofaunal diversity, soil enzymes). The degree to which the TSBF BGBD project meets this need should be considered and complementary work proposed as appropriate.

Figure 3 shows a declining yield trend over a period of time under a consistent and continuous land management system, i.e. crops or pastures, indicating a gradual loss of soil health. Where the selected indicator or suite of indicators of a particular land management option falls below the threshold value, it can be considered as an indication of poor soil health. This threshold value is the lower limit of system performance. At this point, the land management system will become unsustainable and a high investment will be needed in the recovery of the degraded land (restoration of soil properties and function). The upper line is the optimal situation or target value. It reflects the situation under a healthy pasture (deep rooting, good soil cover, etc.). In reality, the inputs and outputs vary over time (weeks, seasons and years) but should generally balance each other, so that the system oscillates between both limits, maintaining a relatively constant value.

Figure 3. Target values and thresholds for soil health indicators

In terms of sustainable land management, the threshold value may be considered as the level of a specific indicator beyond which the particular system of land management is no longer sustainable. However, the understanding of likely thresholds is not well developed except for a limited number of environmental indicators, such as soil acidity, nutrient status of P and K for a given soil type, and some biophysical indicators such as bulk density. It would be expecting too much for a single threshold value to represent the boundary or cutoff between sustainable and unsustainable. Consequently, a range of threshold values and temporal trends for particular indicators is required. Often, a combination of indicators may be needed.

Target values vary for different soils and for different land uses. Therefore, measurements of the indicators should be made over suitable time intervals using standard methodologies. Establishing acceptable trends requires appropriate methodologies and a common framework is essential to develop national and international standards for purposes of comparison. A key problem will be sample-to-sample variability. This will necessitate robust sampling and statistical analysis protocols if significant trends are to be discerned from a very noisy signal. The use of indicators of soil health helps to define the sustainability and health of the system (Pankhurst et al., 1997). There is a wide range of proposed soil health indicators. However, in terms of productivity, perhaps the best indicator relates to the yield trends under a given management system (Figure 3).

In developing indicators, target values and thresholds, the following projects are notable:

• the above-mentioned TSBF BGBD Network project on the Conservation and Sustainable Management of Below-ground Biodiversity supported by the GEF (US$9 million; with cofinancing an estimated total of US$22 million) for seven countries (Brazil, Mexico, Côte d’Ivoire, Uganda, Kenya, India and Indonesia) to be executed by the TSBF of the International Center for Tropical Agriculture (CIAT). (http://www.tsbf.org/index.htm);

• the European BIOASSESS research project (cofunded by the EC under the Global Change, Climate and Biodiversity Key Action of the Energy, Environment and Sustainable Development Programme) is developing biodiversity indicators or tools for the rapid assessment of biodiversity. It is also measuring the impacts on biodiversity, including that in the soil, of major land use change in eight European countries. (http://europa.eu.int/comm/research/eesd.html);

• the Land Degradation Assessment in Drylands (LADA) project, a GEF-funded project supported by the United Nations Environment Programme (UNEP). FAO is executing this project, for which the methodology development is ongoing under the project development phase with Argentina, China, Tunisia, Senegal and multiple partners. (http://www.fao.org/ag/agl/agll/lada).

Both projects respond to the needs of parties to the CBD and to the Convention to Combat Desertification (CCD). They deserve close coordination among experts and supporting efforts in order to ensure the prompt dissemination of research findings and tools for promoting sustainable agricultural systems and practices and the restoration of degraded lands.

National capacities need strengthening for improved soil biological management, especially in agricultural research and extension, including participatory technology development and adaptation, soil health monitoring and evaluation, and priority setting, with attention to agricultural policy and planning. South-South cooperation, allowing intercountry exchange, could help disseminate appropriate technologies, for example:

• between Latin America and Africa on no-tillage approaches and technology dissemination processes for BNF;

• between Australia and other countries on soil health reporting and indicator development;

• between Cuba and other countries on organic matter and nutrient cycling technologies, such as vermicomposting and N fixation.

Development and adaptation of productive and sustainable agricultural management practices

Integrated ecosystem and adaptive management approaches for soil health

As a basis for the discussions on adaptive management, reference was made to the operational objectives for adaptive management as defined by the CBD (annex to Decision V/5): “To identify management practices, technologies and policies that promote the positive and mitigate the negative impacts of agriculture on biodiversity, and enhance productivity and the capacity to sustain livelihoods, by expanding knowledge, understanding and awareness of the multiple goods and services provided by the different levels and functions of agricultural biodiversity.”

Specific attention was drawn to the International Workshop on Soil Health as an Indicator of Sustainable Management, held at the GAIA Environmental Research and Education Centre, Kifissia, Greece, 25-29 June 1999 (Box 1). This provides an important basis for the discussions.

In addressing this theme, reference was made to the meaning of adaptive management (Box 2). This is a formalized process of decision-making for improving continually the interactive management of ecosystems by learning from the outcomes of operational plans. The concept was developed to address the problems of natural resource managers, who typically face an enormous set of variables as they make decisions affecting the environment. Gathering and digesting huge amounts of information to eliminate uncertainty often leads only to more questions, which lead to more information gathering, more questions and, ultimately, deferred decisions.

The Londrina workshop confirmed that, in order to improve agro-ecosystem management, stakeholders need a greater appreciation and recognition of:

• the effects of soil biota on soil physical, chemical and biological properties and processes and on the air and water resources with which the soil interacts;

• the benefits of those interactions in terms of crop and rangeland productivity and of enhanced C sequestration and mitigation of greenhouse gases.

Soil biota can increase or reduce agricultural productivity depending on their composition and the effects of their different activities. Vice versa, farming practices modify soil conditions and, hence, soil life, including the total number of organisms, the diversity of species, the activity of the individual organisms and the aggregate functions of soil biota. These changes can be beneficial or detrimental to the functions and regenerative capacity of the soil biota. Thus, the activity of soil organisms and land management practices requires effective management for maximum productivity and sustainable use of resources.

The web of life in the soil is a very complex and rich component of agricultural biodiversity and has important interrelationships with other components of the ecosystem. Human management practices influence its functions and activity both directly and indirectly. Thus, it needs to be addressed through an ecosystem approach.

Land managers need unbiased information that will enable them to develop biologically based management strategies to control or manipulate soil stabilization, nutrient cycling, crop diseases, pest infestations, and detoxification of natural and human-made contaminants. Such improved management strategies depend on a good understanding of soil organisms and their ecological interactions and of the effects on soil biota of habitats, food sources, host interactions, and the soil physical and chemical environment. The ecology regulating both beneficial and detrimental organisms is essential to harnessing and controlling their activity in agro-ecosystems. Such knowledge will yield great benefits in terms of the production of abundant, high-quality agricultural products with less dependence upon external inputs.

A vast range of innovative soil management practices involving biota and biotic products is available. Moreover, many of these practices are sustainable, environmentally friendly, affordable and applicable to developing nations. Many of the tools are based on traditional agricultural practices, while others are novel and take advantage of recent major advances in biotechnology. Biotic solutions should be encouraged in order to address the wide range of soil-related physical, chemical and biological problems.

The goal is to understand the soil biota and to utilize this living component of the soil for the benefit of agricultural systems in order to increase crop productivity and quality, reduce input costs, and reduce negative environmental impacts.

The review of cases and discussions during the workshop led to the following general guidelines for soil management and sustainable agriculture:

• An integrated agro-ecosystem management approach is required for the review and development of better soil biological and other farming practices in view of the interactions among plant diversity and other resources, management practices, knowledge and organizational capacity (resource use in space and time). Attention needs to focus on biophysical, socio-economic and policy aspects, as well as on cultural and knowledge considerations that influence decision-making processes.

• The process must be interdisciplinary in order to address the interactions among plants, the soil, organic matter inputs, moisture, pests and diseases, soil biological activity and productivity.

• Farmers’ needs and problems, such as labour, weed control, and water or pest management, should be addressed through an initial entry point. This can facilitate a process to build an integrated soil biological management approach. Such a process should combine biological, physical and chemical management issues. It should address productivity and environmental sustainability.

• Adaptive management and integrated ecosystem approaches require scientific rigour and a joint learning process among different actors. This should build on farmers’ knowledge and on scientific knowledge and research. The farmer’s perspective is essential as the management practices and opportunities in terms of soil biological management depend on socio-economic conditions and local knowledge systems.

• Sustainable biological management is not simply a question of managing nutrients. Primarily, it entails restoring the productive potential (as many lands are already degraded) and enhancing the efficiency of soil management (soil-crop-water interactions).

• There is a need to value the ecosystem services provided and to quantify the on- and off-farm benefits provided by sustainable biological management in agriculture (reduced costs of water purification and infrastructure maintenance; C sequestration; biodiversity conservation; etc.).

• There is a need to expand the education process to: (i) build capacities at field and planning scales for integrated agro-ecological approaches at all levels, from schools to universities; (ii) to educate and sensitize policy-makers on the importance of soil biological functions and sustainable agriculture; and (iii) to empower communities and civil society organizations for lobbying, decision-making, etc. This recognizes that on certain sensitive issues, e.g. access to and safe use of pesticides and fertilizers, international processes may be better placed to convince policy-makers than scientists, in view of issues of status, neutrality, etc.

• There is a need to promote participatory, grassroots-driven processes to facilitate the adoption of better soil biological management and sustainable agriculture. This requires attention on how to build on and promote community organization and networking; concepts of land care and stewardship; gender issues; and appropriate technology options for end users.

• Cooperatives and farmers’ associations that are farmer-driven, as in the case of no-tillage in Brazil, can help reduce initial risks for individual farmers, improve awareness and access to information, facilitate negotiation, and enhance farmer empowerment and lobbying capacity to bring about policy change.

• FFS approaches and other learning-by-doing (experiential) approaches are very useful for improving technology adaptation and exchange, taking into account local constraints and opportunities.

• Economic considerations are the primary driving force for the adoption of unsustainable agricultural practices (e.g. steep-slope cabbage production in Haiti; and the shift from coffee to annuals in monoculture and the degradation of common property resources such as pastures and range in Brazil). The low benefit-cost ratio of agriculture is a key issue. Is compensation for the ecosystem services provided by farmers the only option, or are there other ways (e.g. certification for good practice, added value for farm produce through organic agriculture)?

• The search for good practice also requires incentives to encourage adaptive management approaches, e.g. in regard to access to credit and extension, security of tenure and access to resources: (i) to encourage farmer investment in sustainable land use there is a need for security of access to resources; (ii) to promote holistic and flexible credit systems to meet multiple needs and replace credit that is linked directly to cash crops, as was the case with the green revolution process; and (iii) to move away from package approaches to adaptive management approaches that take into account sustainability issues in relation to the complex of different types of farmers and farm households.

• There is also a need to mobilize a sense of responsibility and accountability: (i) for the adoption and promotion of good farming practice by farmers; (ii) for government compliance to fulfil commitments to implement conventions and agreements at all levels; and (iii) for responsible practice by agro-industry. In the case of no-tillage, for example, the private sector is interested in sales of herbicides and seeds rather than in cover crops and crop rotations, which are essential for sustainability and help minimize the use of chemicals.

• There is a need to document the processes and methodologies for intervention, technology development and adaptation, as well as activities and impacts. In this regard, case studies should document both successes and failures.

• Besides the agriculture sector, there is a need to consider wider development issues of rural exodus, the desire for modern amenities (education, television, etc.), the need for greater recognition of agriculture and well-being in rural areas (air quality, quality of life, etc.), and the provision of basic services and amenities (electricity, communication, etc).

Figure 4. Diagram of an adaptive management framework for soil ecosystems: entry points and opportunities for intervention

The Londrina workshop participants suggested the preparation of a schematic diagram of an adaptive management framework for soil ecosystems (Figure 4).

Sharing experiences and lessons learned and identification of gaps and priorities

The basis of all efforts to conserve biodiversity and natural ecosystems effectively while supporting economic development lies in the ability of scientists, resource managers, policy- and decision-makers, and the concerned public to have the widest possible access to the existing body of knowledge on biodiversity and ecosystem resources and processes. Much information exists on biodiversity and ecosystems (from a legacy of past research and inventories), and much more is being collected. However, it is still not possible for all potential beneficiaries to locate, retrieve, integrate and apply this information in a consistent fashion. In many cases, public and private funds are spent unknowingly on re-collecting information that may already exist in some undocumented or unavailable fashion. Much existing biodiversity and ecosystem information cannot be used widely (and may be in danger of being lost) because, for example, it is not yet converted into an electronic format or other readily usable form.

There was a suggestion to make a user-friendly inventory of projects and activities upon which to build for the development of guidance, tools, approaches and materials for different scales, systems, etc., for example, the TSBF, the IRD, FFS-soil productivity improvement, watershed management projects, promoting farmer innovation and local knowledge systems, PLEC. The products and expertise of these projects and processes could provide guidance for specific systems and situations for, inter alia:

• restoration of soil productivity and degraded systems;

• reclamation of degraded and contaminated lands (salinity, toxicity, etc.);

• minimizing use and negative effects of agrochemicals;

• improvement of resource use efficiency;

• enhancement of agricultural biodiversity (systems, habitat, landscape, above-below-ground links);

• enhancement of specific soil biological functions (nutrient cycling; C sequestration and reduction of greenhouse gas emissions; biological control of pests and diseases), and water movement and soil moisture retention;

• sustainable intensification.

There was also a suggestion to develop a checklist and format for case studies in order to enhance their usefulness in terms of clarity and eventual replicability. There was also a proposal to prepare a conceptual diagram linking the different dimensions, to facilitate review and analysis, as initiated by the adaptive management group. The case-study format should specify, inter alia, the following information:

• agro-ecological zone and geographical area (e.g. dryland; subhumid; tropical, temperate; and soil, water and vegetation resources);

• farming system type including farm size and level of intensification (e.g. smallholder low external input agriculture (LEIA) or commercial high external input agriculture (HEIA), crop and livestock focus and range of enterprises);

• spatial scale (field, farm, region, country) and temporal scale (season, year, decadal growth cycle, e.g. of tree crops);

• actors/stakeholders and their roles and interactions;

• specification of the problem and farm household type being addressed. Who identified the problem? Who identified the solution?

• socio-economic and cultural context;

• ecosystem approach: extent to which the activity fits within an integrated ecosystem approach;

• processes and methodologies for interventions, technology development and adaptation (i.e. extent to which they are multidisciplinary, multistakeholder and participatory, and farmer-, extension- or research-driven processes);

• activities and expected results: e.g. categorized in terms of assessment and monitoring, capacity building, adaptive management and technology development, mainstreaming through dissemination, policy advice, advocacy and awareness raising;

• social organization and processes for farmer experimentation and building on farmer innovation;

• marketing, institutional and policy considerations;

• products, impacts and lessons learned (specific to the site and applicable elsewhere) with a focus on practical outputs (approaches, tools, capacity, expertise, know-how, i.e. number of farmers reached or technicians trained) and including attention to productivity, sustainability, biodiversity and ecosystem resilience.

A particular strategic issue that the workshop identified was the need to enhance understanding of the benefits and value of soil biological activity and soil ecosystem functioning, illustrating, inter alia:

• the relationship between good soil properties (physical, chemical and biological) and crop yield and health (e.g. synergies and interaction between integrated production and pest management (IPPM) and integrated soil and nutrient management (ISNM) - balanced plant nutrition, beneficial organisms, etc);

• the effect of excess inorganic fertilizers, herbicides and pesticides on plant health, growth and production, and on agro-ecosystem function (including issues of resilience, nutrient uptake, food web, etc.);

• the effect of monocultures on soil biological activity compared to crop rotations and mixes that provide organic matter inputs;

• the performance of organic agriculture and agro-ecological agriculture (intercropping, organic matter inputs, etc.) and their capacity for biological buffering and gradual release of nutrients to meet plant needs (major, secondary and trace elements);

• the benefit-cost analysis of different practices, with a focus not just on market-driven considerations (production and income) but on assessing and valuing the range of goods and services provided by integrated soil biological management (food security, environmental and human health, etc.).

The other main strategic issue identified was the need to develop an approach that focuses on organic matter within a systems approach including technical, socio-economic, cultural and policy and institutional considerations, specifically:

• the identification of resource- and input-efficient systems that balance internal and external resources (energy, fertilizers, pesticides, soil capital, etc.);

• increased attractiveness of agriculture through reduced drudgery and enhanced well-being of farming communities;

• building on indigenous knowledge, where appropriate, and modern scientific knowledge so as to enhance credibility of the local practices, knowledge and decision-making processes.

It was suggested that case studies be compiled for each category of soil biological solutions in order to demonstrate the valuable role and functions of soil biodiversity and related ecosystem functions in different farming contexts. Three key areas of intervention include the production system as a whole, organic matter management, and the cropping system or plant-soil interface.

Sustainable production systems

Soil quality, landscape quality, soil biota, nutrient cycling and biodiversity are integral aspects of sustainable development. A holistic, ecological approach is required for future research on soil-plant-animal systems. This will enable redesign of farming systems from an overemphasis on production towards more quality and internal regulation. This will result in lower mineral fertilizer losses, lower pest and disease pressure, and reduced susceptibility to climate extremes, thereby contributing to sustainable land management on-farm and at regional scale.

PLATE 6. A mixed arable-livestock system from the Eastern Plains of Colombia - [ J. J. Jiménez]

Organic matter management and the soil ecosystem

Primarily at a functional group level, soil biota regulate vital ecosystem processes such as decomposition (the breakdown of complex organic compounds into nutrients available for plant growth), C sequestration, and nutrient cycling. The rate of decomposition is dependent on the interaction of climate, biota and the quality and quantity of organic matter.

Agricultural practices that provide good soil protection and maintain high levels of soil organic matter favour higher biodiversity. Examples include agroforestry systems, intercropping, rotational farming, conservation agriculture, green-cover cropping and integrated arable-livestock systems (Plate 6). Actions that target the joint conservation of both above- and below-ground components of biological diversity directly will have environmental benefits at ecosystem, landscape and global scales.

The cropping system and the soil ecosystem

The successful functioning of most ecosystem processes requires a balance of biotic interactions in a complex soil biota community (detritus food web). Availability of C is one of the important regulating factors of biological activity in soils, which affects the composition of the microbial community and the food-web structure. In addition, the number of trophic levels in a terrestrial food-web community and its stability depend upon the amount and quality of C input and the level and type of disturbance (e.g. tillage, genetically modified (GM) crops and use of agrochemicals).

Plants are the main drivers of the dynamics of soil microbial communities via their input of various C sources into the system. Plant residues are the primary source of C in soils, with the majority of biota populations concentrated near residues and in the rhizosphere of plants. Therefore, any changes to the quality of crop residues and rhizosphere inputs will modify the dynamics of soil biota. Hence, a change in vegetation as a result of changes in land use is a major factor affecting the diversity of the microbial community. Moreover, changes in agricultural practice including the intensity of the use of fertilizers and pesticides and crop cover, e.g. grass versus arable crops in rotation, may lead to shifts among and within groups of the microbial community.

Diverse habitats support complex mixes of soil organisms. Diversity can be achieved with crop rotations, vegetated field borders, buffer strips, strip cropping, and small fields. Crop rotations provide different food sources into the soil each year and encourage a wider variety of organisms and prevent the buildup of a single pest species.

Soil resilience and risk alleviation

Because of time constraints during the workshop, the working group on innovation and risk management agreed to exclude the important issue of genetically modified organisms (GMOs), and to concentrate on other organisms, technologies and methods, including peri-urban and waste management issues (e.g. vermicompost). The knowledge and experience among participants was reviewed, taking into account the different biophysical conditions and range of functional groups: the producers, consumers and decomposers (N fixers, P solubilizers, C and N mineralizers, predators, pests and pathogens, soil aggregation engineers, antibiotics). It was agreed to keep a focus on food security, environmental quality and economic sustainability goals. A holistic systems view is needed to address extensively managed systems, such as shifting cultivation, intensive diverse systems and monocultures.

The first role of biodiversity is to ensure the multiplicity of functions that soil organisms perform. A secondary but important role of biodiversity is to ensure the maintaining of these functions in the face of perturbations. Genetic variability within and between species confers the potential for resistance to perturbations, whether they be short or long term. Understanding the relationship between biodiversity and more complex functions requires the combined study of taxonomically distant groups of organisms that can perform specific functions, and thus belong to the same functional group.

The group considered available solutions for addressing a range of soil fertility deficiencies and land degradation problems that are mediated by soil organisms and their functions, summarized in Table 3. The analysis in Table 3 can be updated through further consultation and sharing of examples, e.g. in FAO’s electronic workshop on composting (http://www.fao.org/landandwater/agll/compost/).

Soil microbial communities represent the largest source of biodiversity on earth. Given the extremely high species diversity in soil, it is estimated that microbial communities contain such high levels of redundancy as to make small changes in soil microbial diversity insignificant. Rather, shifts among groups or species within the microbial community are considered to be of much more relevance for the functioning of terrestrial ecosystems. Shifts that might be relevant for sustainable land use include those in the relative abundance of bacteria and fungi and within groups with specific functions, such as nitrifying bacteria. These shifts could affect vital functions of the soil ecosystems, such as nutrient retention and antagonism against plant diseases.

A greater degree of biodiversity between or within a given species or functional group should logically increase the inherent variability in tolerance or resistance to stress or disturbance. Implicit in these arguments is the assumption that a multiplicity of organisms can perform a particular function, and that the replication of the ability to perform a particular function implies a degree of functional redundancy. Whether organisms are ever truly redundant is a matter of debate. Though redundancy in a single function may be common among many soil biota, the suite of functions attributable to any one species is unlikely to be redundant. Furthermore, functionally similar organisms have different environmental tolerances, physiological requirements and microhabitat preferences. As such, they are likely to play quite different roles in the soil system.

Table 3. Soil biological solutions for soil fertility and land degradation problems

Possible soil biological solutions:

Aggregation, porosity, regulation of soil hydrological processes - these are improved by bioturbating organisms, plant root, fungal hyphae, microbial secretions.

Bioremediation.

Nutrient cycling, decomposition of organic matter, nutrient mineralization, N fixation.

Crop diversity over space and time (intercropping, diverse rooting depths, rotations).

P solubilizing bacteria and plant nutrition and plant growth promoters.

Suppression of pests, parasites and diseases.

- Unlikely to have beneficial impact
+ Positive impact expected

However, given the estimates for the vast numbers of species present in soils, and the rather limited number of functions that can be ascribed to the soil biota as a whole, a degree of functional redundancy seems inevitable even allowing for the fact that decomposition of plant material may require hundreds of enzymes. The greater the degree of functional redundancy, the greater will be the ability of a particular function to withstand stresses or disturbances, i.e. the greater the resilience.

Any novel method for manipulating and managing soil biodiversity and biotic products in situ requires an analysis of risk. There has been considerable interest in evaluation of risks associated with GM crop varieties. However, apart from these cases, little serious attention has been paid to environmental impact. This is the case especially where microbial treatments or manipulations are carried out. For example, little is known of the effect of Rhizobium inoculation on natural microbial populations. Similarly, the effects of herbicide-resistant plants and the use of herbicides on the soil ecosystem are not well known. It is not acceptable to assume that biosafety assessments can be made using external measurements, such as plant health or productivity, without doing the basic research to establish the necessary links.

Risk analysis is more complex than the simple establishment of safety in isolation from the environment in which the new product or process is to be employed. The following issues need to be addressed:

• Toxicity: is the product safe to eat for consumers (humans or animals) or can it produce toxic products or by-products?

• Environmental impact: what are the effects on non-target organisms? Assessments should be made of effects on a range of organisms, including providers of key ecosystem services and prominent species such as birds and butterflies.

• Genetic drift: what is the risk of genes from novel crops flowing into the environment? This may happen through hybridization between new varieties of traditional crops and their wild relatives as well as from GM varieties (i.e. the loss or fixation of specific alleles due to random effects associated with breeding in very small populations, technically, in populations below the effective breeding size - D. Bennack, personal communication, 2003). Terminator gene technology can eliminate this risk for GM crops, but some consider it unacceptable.

• Agronomic merit: do the new varieties perform better than those currently in use; and will pesticide needs be smaller or greater?

• Socio-economic issues: will the crops be acceptable to farmers, and do the farmers have access to any specialized handling equipment needed? For example, a crop designed for mechanical harvesting in the American prairies may not perform well in the small plots of subsistence farmers in Africa.

• Financial: can farmers afford the product, and will increases in production lead to greater income, or a consequent fall in crop price? Will consumers buy the new product? For example, even if Rhizobium inoculants give proven yield increases, farmers will not adopt them unless their availability is accompanied by information and training on their use and demonstration of the potential benefits of investing in such a product.