A typical teaspoon of agricultural soil contains more than a billion bacteria of several thousand
different species, a million other single-cell organisms, a million individual fungi, and
hundreds of larger creatures.
This biodiversity plays a key role in the ability of soil to support plant life, including
agricultural crops.
Earthworms are the most important of the easily visible creatures, acting as the chief engineers
of soil structure and providing material for finer decomposition by their microbial colleagues.
Worms are also an indicator of soil health, being affected by matters such as acidity,
waterlogging, and compaction.
They’re easy to identify and count, but with soil microbes, that task has been far
harder.
However, new molecular fingerprinting technology known as metagenomics is coming to the rescue.
Scientists can take a soil sample and sequence all the DNA in it. Then, powerful computer
programs then try to sort out the various contributing organisms.
The first attempt to build a global atlas of soil microbes mapped around 25,000 types
of bacteria.
At a biological level below bacteria, are the viruses that infect them, known as phages,
but their impact on microbial activity in soil is still almost entirely unknown.
Another challenge is determining the best way for farmers to use this new soil composition
information.
For example, one of the biggest changes in European arable farming recently has been
to drill seeds directly into the soil without tilling or ploughing.
Minimum tillage increases biodiversity in the upper layer as organic material builds
up, but it’s still not certain if this improves crop productivity or its ability to store
carbon.
The knowledge may still be a little muddy, but as soil quality and maintenance rises
up the political and environmental agenda, so will the sophistication of methods to assess
the impact of its myriad crucial inhabitants.