Soil Fertility

  1. What is soil biological fertility?
  2. What are the ten key principles of soil biological fertility?
  3. What are the corresponding land management guidelines relating to these ten key principles of soil biological fertility?

Question 1: What is soil biological fertility?

Soil fertility is the combined effects of three major interacting components. These are the chemical, physical and biological characteristics of the soil. The physical and chemical characteristics of soil are far better understood than that of the biological component, therefore we know quite a lot about the desired chemical and physical status of soils. It is still difficult to define the desired biological status of soil because they are so dynamic and changes occur in much shorter time periods than physical and chemical changes.

Biological fertility, while difficult to define, provides us with great opportunities for land management and monitoring because of its dynamic nature. It is thought the biological state of soils may be able to provide early warning of land degradation, therefore enable us to employ more sustainable land management practices.

The biology of soil is complex and we need a better understanding of the mediatory effect that biological components have on chemical and physical fertility. We have yet to determine desirable levels of activity, numbers and diversity of soil organisms to maintain a fertile and productive soil.

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Question 2: What are the ten key principles of soil biological fertility?

The biological components of soil perform a number of important processes, soil biological fertility :

  1. Soil organisms are most abundant in the surface layers of soil,
  2. Soil organic matter is naccessary for nutrient cycling and soil aggregation,
  3. Maximum soil biological diversity depends on the diversity of organic matter and habitats,
  4. Nitrogen fixing bacteria form specific associations with legumes under specific conditions ,
  5. Nitrogen is released during organic matter breakdow, either into soil or into the soil micobial biomass,
  6. Arbuscular mycorrhizal fungi can increase phosphate uptake into plants in P-deficient soils,
  7. Soil amandments can alter the physical and chemical environment of soil organisms,
  8. Some crop rotations and tillage practices decrease the suitability of soil for plant pathogens,
  9. Production systems based on soil biological fertlity can be profitable,
  10. Soil biological processes develop slowly, and the time required will differ for different soils, environmnents and land management practices.

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Question 3: What are the corresponding land management guidelines relating to these ten key principles of soil biological fertility?

  1. Soil erosion should be controlled to minimise loss of soil organisms,
  2. Plant organic matter should be retained to maximise nutrient cycling and soil aggregation processses,
  3. Some disturbance of soil is necessary to maximise soil biological diversity,
  4. Nitrogen fixing bacteria should be selected that match the host, soil characteristics (such as pH) and environmental conditions,
  5. Inputs of nitrogen fertliser should be calculated to complement nitrogen cycling from organic matter
  6. Inputs of phosphorus fertiliser should be calculated to complement and enhance the activities of arbuscular mycorrhizal fungi,
  7. Any substance added to soil should be assessed in terms of its effects on soil biological processes and soil biological diversity,
  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. 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. Sufficient time should be allowed for establishment or restoration of a level of soil biological fertility appropriate for particular soils and land management.

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