Soil Structure

Plants, worms, and insects are not the only things living in our soils. There is an incredible diversity of microorganisms that also live there. Bacteria, fungi, protozoa, nematodes, and microarthropods belong to the soil food web and can only be seen with a microscope. All these invisible organisms play really important roles in our soils. They decompose our waste; they produce nutrients for our plants, and they create our soil structure to name just a few. In fact, the science world knows more about our stars than most of the organisms in our soils.

How To Improve The Diversity Of Microorganisms In Your  Soil


  • Reduce tilling, fertiliser and chemical use
  • Diversity above ground = diversity below. Think multispecies.
  • Keep soil covered with mulches or a living ground cover
  • Bacteria like to eat simple sugars – grass/hay/legumes
  • Fungi like tougher, complex materials higher in carbon – woodchip/brown leaves
  • Veggies need slightly more bacteria than fungi
  • Lawn and pasture need equal amounts of bacteria to fungi
  • Trees need more fungi and less bacteria

Beneficial Microorganisms and The Roles They Play


Bacteria are the smallest that we can see. They are like tiny little bags of fertilizers. As they help to break down the organic matter in the soil, they hold those nutrients in their bodies and only release these when they are eaten. Bacteria also make glues that stick our soils together creating micro-aggregates. Just looking under the microscope we can’t tell what species they are but that’s ok as we are looking for diversity. Bacteria are the ones responsible for heating composts. As they reproduce by splitting into two, they create heat.  A compost pile with lots of green waste will grow a lot of bacteria. They like to eat the small simple compounds and store the highest amount of nitrogen of any organism on the planet.


Fungi are like little conveyor belts transporting nutrients and sometimes even water from one area to another. Some fungi grow into the plant roots and some live just on the outside sharing nutrients with plants. Fungi can be found in the form of yeasts, moulds, or filaments. Fungi get a bad name thanks to a minority of disease-causing pathogens. If we have a good diversity of local microorganisms in our soils filling up all the food and accommodation sites, then when a pathogen comes in by floodwaters or blowing in on the air there’s no room left, and they flow past to the next available site. Like bacteria, fungi play an important role in making our soil structure. They are like little ropes pulling the micro-aggregates that the bacteria glue together to form larger aggregates. This creates spaces and allows for oxygen and water to filter deep into the ground. We now find our dams take a bit longer to fill as our soils absorb more water. Fungi like to eat the tougher carbon material. 


Protozoans are a bit larger and love to eat bacteria. As they eat, they produce wastes, and this waste is perfect plant nutrients. Plants can influence biological populations. As plants photosynthesis, they produce an exudate (a dribble of carbon and sugars) from their roots. This attracts bacteria and fungi which then attracts the protozoans to a feast right where the plant wants to absorb the nutrients. One little flagellate can eat up to 10,000 bacteria a  day. That’s a lot of pooping out of nutrients. Unfortunately, if we have been using a lot of fertilisers the plants get lazy and this relationship is broken. You may have seen plants not doing so well when you don’t keep up the fertilisers. They have learnt to be dependent on the soluble fertilisers. Fixing this relationship means weaning the plants off fertilisers slowly.  


Nematodes are the microscopic worms that we can see wriggling under the microscope slide. There are lots of different species and identification can be done by looking at their mouthparts. Some have big lips, they eat bacteria, and some may have little spears and they use these to pierce fungi. The ones that cause the main damage in our crops are the root feeders and they are easy to identify as they have a small knob that is a muscle that they use to project their spear into the root systems. Some nematodes are cannibals in that they eat other nematodes. Really good to have these if you have problems with root-feeding nematodes.


Soil biology report

Understanding Your Soil Microbes

Working with the soil microbes starts with a basic understanding of what affects them.  Unfortunately, most of our farming practices have an impact on their environment. Tilling,  chemicals, and fertilisers all have an effect. Minimising these 3 will see benefits to their populations. All the beneficial microorganisms need oxygen and most of the disease-causing pathogens live in low oxygen environments. This makes compaction a real problem for beneficial organisms. Organic matter (food and moisture for the microbes) needs to be a minimum of 3%. Otherwise, microorganisms will struggle, especially in sandy soils and especially when no plant exudates are present like times of fallow. Organic matter holds a  lot of water and these microbes need moisture otherwise they go dormant (form a spore) till the moisture returns. If you want to keep food for a long time, a good way is to dehydrate it. This stops bacteria from breaking it down and it’s the same in our soils.  

All these organisms are not just underground they also occupy all the spaces on the leaves,  the flowers, the trunks, or stems of the plants. When we gather organic matter to make composts, we also are introducing these organisms to the composts. When we eat plants,  we are also introducing microorganisms to our bodies. How your food is grown has a big effect on your own biome.  

To get your soil analysed, get a Soil Biology Report here.


Article printed in the May issue of  ‘What’s On & Where to Go