What makes a “good” soil? Physical and chemical characteristics like friability and acidity? Sufficient nutrients in appropriate ratios constitute fertility? Increasingly, scientists are looking to the role soil biodiversity plays in supporting plant life. We know that many of the important ‘services’ provided by soils depend on the build-up of organic matter. Yet, it turns out that there’s still so much we don’t know about the role of micro-organisms in soil health and thus plant productivity.
Did you know?
The European Soil Data Centre found that a 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
- hundreds of larger animals such as worms and insects
… All in one teaspoon!
What we know about earthworms
When it comes to soil health, earthworms are the ‘chief engineers’ of soil structure. They consume leaves and other plant material and their excretions undergo finer decomposition by other microbes. They are also a vital food source for reptiles, amphibians, birds and mammals, further increasing the biodiversity of the ecosystem.
The presence of worms in the soil is also an indicator of the health of the soil, as they are affected by tillage, rotation, organic matter management, compaction, waterlogging and acidity. Damage to the soil generally means a decrease in its earthworm population. In the UK, farmers are even encouraged to count the number of earthworms found in 20cm cubes of soil in order to assess its quality.
What we don’t know about soil microbes
Trying to count and identify soil microbes is a much harder task than counting earthworms, even in a lab, where fewer than 5% of them can be isolated and cultured in the lab through conventional microbiology.
Scientists are now relying on “metagenomics” – new molecular fingerprinting technology in the form of genetic sequencing and data analysis. Here’s how it works:
- Scientists can take a soil sample and sequence all the DNA in it from different microbes.
- Powerful computer programmes try to sort out the various contributing organisms.
The early results of this testing are being used by researchers to build up databases of soil microbes.
Digging even deeper into the unknown
Below bacteria at a biological level are phages, the viruses that infect bacteria. At this stage, their impact on microbial activity in soil is almost entirely unknown. However, a team at Pacific Northwest Regional Laboratory is attempting to use new technology to map the global soil virome. The next step is to understand what these phages are actually doing in the soil.
To till or not to till?
Over the past few years, farmers have begun to drill seeds directly into the soil to limit or eliminate the need for tilling or ploughing. But a new debate has sprung up around whether tilling improves or degrades soil health. Minimising tillage increases biodiversity (and thus soil health and crop productivity) in the upper layer of the soil as organic material builds up. Although there’s an increase in carbon in the topsoil when there is no tilling, there can be a decrease in carbon further down in the soil in the long term due to lower soil disturbance and carbon redistribution.
As you can see, despite ongoing research, there is still a lot for us to learn about soil health and its contributing factors. With the threat of the depletion of natural resources rising up on political and environmental agendas, scientific discovery around soil health isn’t going away anytime soon. At Zylem, our goal is achieving healthy soil in Southern Africa. Get in touch to find out more about our sustainable services and solutions: https://www.zylemsa.co.za/contact-us/.