Soil ecology as it relates to soil improvement

Soil ecology is a relatively new field, especially in terms of its practical application to soil improvement. One problem is in getting a picture of the soil ecosystem that is not influenced by seasonal changes. In other words, one will show you the same things whatever time of year you look at it. The answer to this lies in restricting the view to only those organisms that are 'active' at the time. The activity of soil organisms may go up or down, but when introduced to the 'ideal' conditions provided in the laboratory, they will always be the first to grow.

The practical application of soil ecology is a very new field

Recent research has cast new light on the nature of the soil's biological community with some unexpected results that indicate a much closer link between the physical environment within the soil and soil biology than was previously expected.

The research was aimed at better understanding the inter-relationships between physics and chemistry in the soil together with soil ecology as predicted by the Mikhail System.

Of course, a proper understanding of soil biology and its place in the soil balance system requires an understanding of the Mikhail System itself.

If you have not done so already, you should read our information about the Mikhail System before going on with the information on this page.

The first breakthrough for the practical application of soil ecology came when researchers at SWEP laboratories in Australia were analyzing their data to try and identify possible correlations between their soil biology test results and other soil tests. At first their results showed an almost random ‘scatter’ with no apparent relationship to any of the usual soil test measures, but when they focused only on samples showing cation balance levels that were 70% or more of the ideal proportions, patterns suddenly began to emerge that clearly indicated soil physics would have a far greater impact on soil ecology than nutrients.

The ideal proportions for the five major soil cations are:

Calcium	65% to 70%
Magnesium	12% to 15%
Sodium	Less than 5%
Potassium	3% to 5%
Hydrogen	Less than 10%

The researchers were then able to show that the total population (of the five microbial indicator groups they were measuring) was directly related to the Adjusted Cation Exchange Capacity , but only in well-balanced soils. Also, in such well balanced soils, the component microbial groups were present in fairly consistent proportions, relative to the desirable total that was calculated from the Adjusted CEC.

Lactic acid bacteria	17%
Yeast	16%
Photosynthetic bacteria	13%
Actino-bacteria	21%
Fungi	33%

This had important ramifications for soils with less than optimal balance proportions of exchangeable cations, since many such samples showed active populations far greater than the desirable level that was calculated from the Adjusted CEC.

What was going on in these poorly balanced soils and what changes needed to take place as they were improved?

The problem was that there was no simple progression of change in soil ecology as there was with the cation balance. For instance, when a soil is low in exchangeable Calcium and high in Hydrogen, you simply add Lime. The Calcium goes up and the exchangeable Hydrogen goes down, while the other cations remain more or less unchanged. By contrast, the balance of soil ecology is much more complex and dynamic, with many changes occurring in all the groups before they finally settle into a stable balance.

Gradually, a picture began to emerge. Poorly balanced soil ecology often seemed to be dominated by one particular group at the expense of others and it seemed to be the Lactic acid bacteria that were a common culprit. Their numbers could be hugely excessive, while other groups were poorly represented. Yeasts were another group that seemed to behave in this way, while photosynthetic bacteria appeared to be the dominant group in soils with very low microbial populations.

This shows that soil ecology is still a complex field, but as we get a better picture of how the soil ecosystem functions we can paint a 'picture' of how it operates that draws on parallels we see with life in our own cities. Painting mental-pictures like this may seem a bit silly, but it helps us better understand what is really going on.

To do this, more information was still needed and so two additional measures were developed – called Occupancy and Suppression.

The first measure is “Occupancy” – what percentage of the desirable population does the measured population represent? Is the soil a Ghost Town or a bustling Metropolis? Is it under-populated by hard-working people, or over-populated with undesirables?

As soil balance improves, the Occupancy percentage either decreases towards the desirable, or (if the soil has been degraded to a state analogous to that of a Ghost Town) it increases towards the desirable. The question then is “Why is the occupancy level so high or so low?” and this seems to relate to a measure called the ‘Suppression Index’.

This is the extent to which organisms such as Yeast and Lactic acid bacteria inhibit the activity of others (a value of 1.0 would represent total suppression, while zero is none at all).

You could imagine a high Suppression index for soil ecology being like a high Crime rate in the City – the ‘good people’ become reluctant to leave home and go to work – their activity is suppressed.

And so we can now build a picture of soil ecology as being like a 'City in the Soil' and see the various conditions that may exist:

1. 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).

2. 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.

3. 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.

4. 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 is 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 soil ecology 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 soil 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 everywhere.