The living soil ecosystem in some ways resembles a City.
Rather than think of soils as simply dead or alive, it may be more helpful to think of the soil ecosystem as being like a City in our Soil and see the various conditions that may exist: - The Ghost Town: Where occupancy is low and mostly made up of ‘hermits’ who eek out a living on very little. The streets are full of potholes and tumbleweeds, the living conditions (physical environment) so undesirable that only the toughest can survive.
This would be a highly degraded soil. The total population would be below the desirable (occupancy <100%). The predominant group present in these soils is often the photosynthetic bacteria, so the suppression index may not be high, but the cation balance will be poor and nutrient fertility low or showing a serious imbalance (a high level of available Copper for example). - The ‘Wild West’ Town: Here the occupancy level is higher and there are a few productive businesses, but the “shoot-em-up” character of the place still suppresses activity.
This could be an undeveloped or moderately degraded soil. The occupancy level is usually somewhat greater than 100%, but not extremely high. The suppression index is moderately high and cation balance is moderately poor. - The Industrial Precinct: Here occupancy is fairly high, but a substantial proportion of this is made up of undesirables in “low-rent” areas. It’s a bit smelly and dirty and not the place to be walking around at night – fairly productive, but not a pleasant living environment.
This is typical of intensively farmed soils with high chemical fertilizer inputs. The occupancy level is well above 100%, the suppression index moderately high, and there are some issues with physical properties such as friability, etc. - The Affluent Suburb: With tree lines streets, playgrounds for the kids, shops and schools close by and a low crime rate, this is a pleasant place to live.
In well-balanced soils the occupancy close to 100% and suppression index is low, the cation balance will be close to optimal, with moderate, balanced nutrient fertility.
Painting such pictures of the living soil may appear trite, but they serve to illustrate the complex and dynamic relationships present and how these relationships influence the overall state of affairs. The most important feature in determining how the soil will behave remains the cation balance and its impact on soil physics, but the ability to add biology to the picture and create such descriptions takes the soil test beyond being a page of numbers that can only be understood by a handful of ‘experts’, to being a practical management tool for farmers and gardeners everywhere. One point that often gets overlooked in all this is that soil biology cannot be managed in isolation. After all, the living soil - like any other ecosystem - is more than just the organisms it contains. Living things need a suitable habitat in which to survive and resources to utilize. For more information on these related fields, you can use the links below. You can also subscribe to our Free email newsletter - The Food Gardener - to ensure you remain up to date with the results of future research in this field.
Further reading and useful links
Companion planting
Soil biology is also influenced by the kinds of plants being grown, so companion planting is a very good way to ensure good biodiversity in the soil.
Appropriate use of soil cultivation
Like a fire in a forest, digging the soil always causes a disturbance to the biological community in the soil. If you need to cultivate the soil, it is important to use the right method and apply techniques to aid recovery from the disturbance.
Garden Habitat
Here are ecological principles that apply as much to the living soil as elsewhere in the garden.
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