Almost everyone is familiar with the good old stereotypical garden earthworm. These creatures are incredibly important for soil health, and make up a vital part of the food chain, not only providing food for other larger creatures, but also breaking down dead organic matter into absorbable plant food (i.e. nutrients).
There is however, a wealth of other strange and wonderful organisms that live beneath our feet and are essential for maintaining good soil health. In this blog I want to delve into the alien world that resides in the soil, looking in greater detail at the creatures that make it their home and without which, the soil would be a much less diverse and resilient place.
I’m going to be digging up the facts about nematodes, a subject that, due to the sheer species diversity, I could write a whole book on. These bizarre little organisms are a topic of much debate since some species can be detrimental to both plant and animal health (with some parasitic types causing disease and death), whilst other species are incredibly beneficial for creating good balanced soils and ensuring disease free plants. I’m going to be focusing on the ones that help nurture our soils rather than those well-known ones that are the blight of growers all over the world.
Unlike our common garden worm, nematodes are non-segmented and range in size from microscopic (<1mm) up to many centimeters in length – although these are not all soil varieties! These small but mighty worms have managed to successfully adapt to almost every ecosystem on the planet, from the deepest, darkest parts of the ocean to the highest peaks, and from the frozen ice caps to the hot, desolate deserts. Nematodes can also be present in vast numbers, particularly in the soil, often exceeding over one million per square meter. In fact, these tough creatures actually make up a staggering 80% of all individual animals on earth. Amazing considering most of us didn’t even know that they existed!
There are four main groups of nematodes, divided up based on their diet. Interestingly nematode types can be seen at many trophic levels; some are herbivores and feed on plants and algae at the bottom of the food chain, some feast on bacteria and other, more tenacious ones actually predate on other types of nematodes. Based on this information, the four types of nematode are:
- Bacterial feeders – who eat bacteria.
- Fungal feeders – who eat fungi (they actually puncture the cell wall and suck out the internal contents).
- Predatory nematodes – who eat all other types of nematodes and protozoa. Their bad reputation probably derives from the fact that they either eat organisms’ whole (if they are small enough), or they will attach themselves to larger organisms and gruesomely extract the prey’s internal body parts!
- Omnivorous nematodes – which eat a varied diet of other organisms and plant based material.
Location, location, location
As with all other living organisms, nematodes prefer to live near their food source – it makes life much easier for them. Thus, the bacterial feeders will generally hang out near plant roots where large populations of bacteria congregate and the fungal feeders will stay close to fungi in the soil – i.e. near the fungus mycelium. On the other hand, predatory nematodes will be abundant in soils with a high population of nematodes and the omnivores are slightly less fussy, and scavenge whatever happens to be nearby.
Because of this, the quantity and type of nematodes in the soil actually varies depending on what food source is present in the soil. Therefore, the proportion of nematodes in the soil is directly related to the amount of bacteria, fungi and other nematodes in the soil. In addition, less disturbed soils contain more nematodes, suggesting that they are highly sensitive to disturbances that may be present (i.e. ploughing and tilling). Studies have shown that heavily disturbed agricultural soils support significantly less nematodes than grasslands and forest soils.
The Good Ones
The few nematode species responsible for causing serious animal and plant diseases have received an awful lot of attention over the years, but far less is reported about the nematode community that plays a hugely beneficial role within the soil.
Firstly nematodes play a vital role in nutrient cycling. Just like single-celled protozoa, nematodes help release nutrients in plant-available forms; for instance, they contribute to an essential part of the Nitrogen cycle. When they digest bacteria or fungi, NH4+ (ammonium) is released into the soil as a surplus product and can be absorbed by plants.
Not only do nematodes produce plant food, they are also a food source themselves for other nematodes and soil organisms and are sometimes parasitized by bacteria and fungi.
Some types of bacterial and fungal feeding nematodes can actually decrease the population of their prey (i.e. the population of mycorrhizal fungi may actually decrease because they are being over-grazed by fungal feeding nematodes). However, predatory nematodes can help regulate the amount of these bacterial and fungal feeding nematodes by predating on them and keeping them at a steady population. Thus, nematode grazing may control the balance between bacteria and fungi, and the species composition of the microbial community.
Another useful trait of nematodes in the soil is the dispersal of microbes.
Nematodes can help to distribute bacteria and fungi throughout the soil by carrying live and dormant microbes on their surfaces and in their digestive systems. This is particularly interesting in relation to mycorrhizal fungi and the transportation of them into soils that have low mychorrhizal fungi population density.
One last benefit of a soil rich in ‘good’ nematodes is that they can actually help to suppress disease. Although some nematodes can cause disease, others predate on disease causing organisms and can actually be excellent biocontrol agents helping to regulate soil nematode populations.
These mysterious creatures are sometimes ridiculed unjustly or dismissed as unimportant; however they are extremely important in the makeup of a truly balanced, nutrient rich soil and may actually be an extremely useful indicator of soil health. This is down to their huge diversity and their involvement at different levels of the soil food web. They are particularly sensitive to disturbed soils and respond to land management changes in predictable ways. If there are no nematodes in the soil, then either the environmental conditions, or the soil management practices used are not in their favor and should be reviewed.
As with all other biological systems, there must be a balance between soil organisms and other soil properties. Wipe out all the ‘bad’ nematodes using various steaming methods or sterilizing them and you’ll also wipe out the massively useful lot of ‘good’ nematodes that contribute to creating healthy balanced soils.
This system, the incredibly complex soil food web, is the epitome of soil management, and we know that by mimicking this tested method (using all the juicy components of soil including these magnificent little creatures), soils that are wholesome and resilient can be created. We understand that soils with a balanced and diverse range of life are more ‘future-proof’, since they can sustain good soil health without much external input. That’s why, at 59 Degrees, we make it our priority to culture soils that incorporate, not just the raw physical properties of soil, but also a balance of all the biological soil life too – this way we can ensure that the soil provides an excellent environment for optimized growth and an ecosystem that is better adapted for self-sustaining.