Dolomite because it typically contains 24% calcium and 11.5% magnesium, both in the carbonate form, has a liming (pH modifying) effect when applied to soil.
As a result beneficial soil life is stimulated. It is very difficult to measure beneficial soil microbes as we don’t know a great deal about what is there or what ought to be there and by the time the counting process is underway populations will have changed.
Dr Graham Sparling in his 2004 Norman Taylor Lecture stated that “despite being present in very large numbers, soil microbes are reluctant to grow in laboratory culture, and it has been estimated that less than 5% of organisms have been cultivated”.
The reason we should care about soil microbes is because our very survival depends on their existence and the maintenance of a diverse population in excellent health.
As pastoral farmers and growers are producers of food we have a responsibility to ensure that the soil we farm provides a suitable environment for not only beneficial soil microbes but also soil macrobes with the ones best able to seen and counted being earthworms.
If there is a resident population of healthy earthworms then we may assume that there is also a healthy population of beneficial soil microbes, without which we have only rock dust.
There are typically 3 distinct types of earthworms (surface workers, mid range workers, and deep burrowers) in our soils, nearly all introduced from overseas in soil used as ballast in sailing ships and around the roots of trees and plants.
Although they thrive in most friable well-aerated soils they are able to survive in water for quite long periods. They don’t drown in puddles but are killed by sunlight after having come to the surface at night in wet weather in order to relocate.
The ideal temperature for earthworms is 10°C, which is why the greatest number of casts is seen on the soil surface during winter and early spring. Not all worm casts are on the surface with much casting taking place below the surface.
The number of worms in a 25cm spade cube will vary. There is no ideal number as different soil types will support different numbers. Soils with high sand content do not support large numbers as sand is abrasive, and worms need somewhere cool and damp to survive dry summers. Typically between 10 and 30 worms in can be found in a cube of well-managed pastoral soils containing a mix of silt, sand and clay i.e. loam soils.
Initially after making more calcium available earthworm numbers may increase to 70+ per spade cube, however earthworms are macro processors and as the friability of the soil steadily improves earthworm numbers will stabilise based on available food.
The time from egg to maturity is around 90 days so when conditions are favourable rapid increases in numbers can occur. A worm egg is about the size of a match head and usually a dull yellow in colour.
Dolomite apart from being the most effective magnesium fertiliser, and supplier of calcium, is also a proven soil conditioner ensuring soils drain more freely over winter and recover more rapidly from heavy treading damage in wet conditions.