It’s a huge carbon pool, absorbing carbon dioxide from the air – 1,500 billion tonnes of carbon globally – almost three times more carbon than in all above ground biomass including trees, shrubs and grasses. According to the Land Care Research Soils portal, each year unsustainable land management around the globe is responsible for around 24 billion tonnes of fertile soil being contaminated, washed off the land or blown away by the wind. In New Zealand it’s 192 million tonnes a year. (1)

It’s not a speedy process, creating healthy, rich, fertile soil. Its origins start with bare rock and sediment surfaces being weathered and disintegrating under the influence of climate. Over time the surface becomes available to vegetation, lead by lichens (of which we have an abundance on Tiritiri Matangi) which will root in any cracks they can find such as the greywacke we see on the Wattle Track. A thin layer of vegetation will gradually build up and in the fulness of time start decomposition which in turn produces organic acids. These help break down the initial material. As life increases on the surface, biological, chemical and physical weathering continues beneath.

There are more species of organisms in the soil than there are above ground; a handful of soil contains millions of individual living organisms. They help break down animal wastes, fallen leaves and other dead flora as well as fauna and turn it into humus which they then distribute throughout the soil. They also help with maintaining soil structure and water filtering. These include earthworms, lice (of the wood variety), spiders, springtails (a favourite of the North Island robin – New Zealand has two of the largest known in the world, Holocanthella, which can be up to 17mm long compared to the average 1-3mm) and mites, plus microorganisms – bacteria, fungi and archaea.

To give some scope to this vast biodiversity, the Land Care Research page on Invertebrates states there have been 22,000 arthropod species described, with at least that number again waiting to be discovered. Of that approximately 80% are endemic.

For more information on this fascinating subject follow any of the links provided, or download the ‘Soil Atlas: Facts and figures about earth, land and fields’ publication link below: It’s a 68 page free download.