Where does dirt comes from? As for “Why is the sky blue?”, “How does grass grow?” and of course the one about babies, the most popular reply is “Ask your father/mother, can’t you see I’m busy?”
So where does dirt come from? The answer is a combination of geological, chemical and biological processes, with bugs of various sizes, from bacteria to insects and worms playing a vital role. By decomposing plants they produce CO2 and help to dissolve minerals. They extract nitrogen from the air and transfer it to plants. They help to aerate the soil by burrowing.
In the first study of its kind, the UK’s Centre for Ecology and Hydrology has estimated how many organisms there are in Britain’s soil. They reckon there are 12.8 quadrillion organisms (that’s 12,800 million million) in the top 3 inches (8 cm), the layer where most species are found, weighing 10 million tons.
The researchers found two main trends. First, numbers have increased by almost 50% in a decade, but biodiversity declined by 11%. They think this may be due to increases in temperature and rainfall. Warmer, wetter soil means many species can breed more quickly, but species that fail to adapt disappear.
They’re not sure what this means in terms of the soil’s resilience to pressures from climate, pollution and farming or other land use practices. There is a large degree of redundancy in the organisms’ contribution to the ecosystem, with many species capable of carrying out the same function. More data are needed to see whether the result really does reveal a trend or whether it is due to the particular conditions in the years when the sampling was done.
However, as the report notes: “The activities of the soil biota are critical for the provision of many important soil functions and resulting ecosystem services. These include… acting as a biodiversity pool from which future novel applications and products can be derived.”
Sustainable agriculture at the OECD