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7.4 Guidelines for land management to sustain soil biological fertility

There are genuine concerns about current land use practices, such as the dumping of toxic substances onto soils and the introduction of genetically modified organisms. Despite the many studies that have shown that improvements can be made and how to make them, society is not well informed about the importance of soil organisms. There is little consideration of soil biological processes during decision-making about land management practices. In fact, decisions are often made as if the soil does not contain organisms that have explicit requirements for their growth and survival based on their life cycles and physiology.

Soils are alive! Soils are not composed solely of inert materials and chemical molecules.

Soil organisms are affected by disturbances to their environment. This simple observation could be the basis for an alternative approach to decision-making in land use. Practices that encourage the activities of beneficial soil organisms are easily identified, for example stubble retention. They need to be recognised as essential to profitable, long-term production, rather than being the first item that is discarded when economic times become difficult. This is a significant dilemma and the land manager should not be left alone to deal with it.

Therefore, society needs to:

• become better informed about the importance of retaining and developing the living component of soil,

• implement policies that reflect the value of the living components of soil,

• be informed about how manipulation of soil alters the activities of soil organisms, and

• understand the implications of all kinds of soil disturbance on productivity, environmental degradation, and the sustainability of all land-use systems.

Land management decisions need to consider the important resource of soil organisms. This applies in any managed ecosystem. Soil organisms have much to contribute to the sustainable use of land in all environments. Below is a list of 10 principles of soil biological fertility is presented based on the range of issues addressed throughout this book. For each principle, corresponding guidelines for land management have been developed. Some of these principles are already implemented; other principles require serious scientific and practical consideration.

Role of soil biological fertility in adaptation to climate change

There is no doubt that soil carbon is a significant pool of the Earth’s carbon resources. The carbon in soil cycles at rates which are influenced by the responses of microbial and soil fauna activities to their immediate environment. Therefore, while some components of soil carbon are more recalcitrant than others are remain in soil for longer periods, the carbon pool as a whole is largely dependent on environmental influences on biological processes.

As climate changes, there is the likelihood that some environments will be come drier and others wetter. This will alter microbial activity – changing the rate of microbial breakdown and consequent rate of loss of CO2 from soil. Where there is a water constraint, plant productivity will be reduced, contributing less soil organic matter to the soil. A consequence of a greater concentration of CO2 in the atmosphere can be increased plant growth, leading to more organic matter in soil, but the soil is a complex system and plant growth responses may depend on the soil properties (Edwards et al. 2003). The higher CO2 associated with increasing global temperatures can have complex interactions with soil microbial communities (Kohler et al 2009, Lipson et al. 2005).

When the beneficial biological processes in soil are considered together, they can make an important contribution to the adaptation of plants and soils to climate change.

Ten principles of soil biological fertility and their corresponding land management guidelines.

Ten Principles of
Soil Biological Fertility

Land management guidelines related to the Ten Principles of Soil Biological Fertility

1. Soil organisms are most abundant in the surface layers of soil

1. Soil erosion should be controlled to minimise loss of soil organisms

2. Soil organic matter is necessary for nutrient cycling and soil aggregation

2. Plant organic matter should be retained to maximise nutrient cycling and soil aggregation processes

3. Maximum soil biological diversity depends on diversity of organic matter and habitats

3. An appropriate disturbance regime applied to soil is necessary to maximise soil biological diversity

4. Nitrogen-fixing bacteria form specific associations with legumes under specific conditions

4. Nitrogen-fixing bacteria should be selected that match the host, soil characteristics (such as pH), and environmental conditions

5. Nitrogen is released during organic matter breakdown, either into soil or into the soil microbial biomass

5. Inputs of nitrogen fertiliser should be calculated to complement nitrogen cycling from organic matter

6. Arbuscular mycorrhizal fungi can increase phosphate uptake into plants in P-deficient soils

6. Inputs of phosphorus fertiliser should be calculated to complement and enhance activities of arbuscular mycorrhizal fungi

7. Soil amendments can alter the physical and chemical environment of soil organisms

7. Any substance added to soil should be assessed in terms of its effects on soil biological processes and soil biological diversity

8. Some crop rotations and tillage practices decrease the suitability of soil for plant pathogens

8. Crop rotations and tillage practices should be selected to avoid development of soil conditions that enhance the growth and survival of plant pathogens

9. Production systems based on soil biological fertility can be profitable

9. The capacity of a management practice to produce a commercial product should be considered in parallel with its capacity to maintain and/or increase soil biological fertility

10. Soil biological processes develop slowly, and the time required will differ with the type of soil, environment and land management practices applied

10. Sufficient time should be allowed for establishment or restoration of a level of soil biological fertility appropriate for particular soils and land management

Summary Points (7.4)

• There has been negligible focus on soil biological fertility in the application of modern agricultural and horticultural technology in spite of the general understanding that small organisms perform highly beneficial functions in soil.

• Sustainable agricultural and horticultural practices, as well as management of natural ecosystems, need to incorporate principles of soil biological fertility and seriously investigate scientific methods for monitoring the benefits of soil organisms, including the natural control of plant pathogens.

• Soil biological processes are essential for sustaining all natural ecosystems.

• Soils contain very diverse communities of organisms and if they are better understood, they will provide an important key to selecting land management practices which are sustainable.

• There are 10 basic principles of soil biological fertility.

• Appropriate guidelines for land management can be matched to each of the 10 principles of soil biological fertility.

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