The symbiotic relationship between plants and soil microorganisms is a crucial aspect of sustainable agriculture. There are millions of different types of soil microorganisms which make up a dynamic micro-ecosystem that inhabits the soil around your crops. These microbes play a vital role in the health and productivity of the soil and plant. By understanding this relationship, we can create the type of soil environment that supports microbial life. This is what we call living soil but what does it really do to help our plants?
Firstly, we need to discuss some of our key organism groups.
Fungi
One of the most important groups of soil microorganisms is fungi, which act as saprophytic organisms by decomposing organic matter. Fungi help to release essential nutrients through the action of their enzymes which digest food sources externally from the fungal hyphae (hairlike fungal structures). These nutrients are mostly utilised by fungi but plants can also uptake a portion of these nutrients. The action of the fungi in the soil also improves soil structure through the release of a substance known as Glomalin. This organic compound is extremely sticky and it helps to stick soil particles together to create an aggregate. An aggregate is a little clump of soil which opens up air pathways known as pore spaces. Aggregation is key to soil structure and the pore spaces allow the transfer of water or oxygen which improve the water retention of the soil. This is a huge factor when faced with more extreme weather events such as droughts or sustained downpours of rain. If your soil has a better structure you can reduce the negative impacts of the extreme weather as your soil will capture more water to store for the dry season.
The next fungi that play a critical role in the soil ecosystem through their ability to form mycorrhizal relationships with plants. Mycorrhizal fungi form a complex and symbiotic relationship with plants by colonizing the plant's roots. The plant receives a number of benefits from this relationship such as helping to absorb essential nutrients, increasing root surface area, protecting the plant from fungal pathogens and improving soil structure. In return, the plants provide the fungi with photosynthetic energy in the form of sugars which the fungi cannot create alone. In soils that have not been fertilised, this relationship is crucial to the uptake of phosphorus which is notoriously difficult for the plant to access in the correct balance. Mycorrhizal fungi have very specific enzymes to change phosphorus from an unavailable form to a bioactive form.
Bacteria
Bacteria are also a critical component of the soil ecosystem and their functions are very similar to that of fungi. Bacteria can replicate every 15-20 minutes under the right conditions. As the most diverse of all the microbial groups, bacteria have many functions in the soil. These functions differ greatly when we compare aerobic to anaerobic bacteria with some of the functions of these two groups being totally the opposite. For example, nitrogen-fixing bacteria will store atmospheric nitrogen in the soil while denitrifying bacteria will release soil nitrogen back into the atmosphere. Due to this wide diversity, we try to ensure we have aerobic bacteria as their functions suit the needs of our crops far better than anaerobic bacteria. Bacteria can help to break down organic matter into simpler compounds that plants can use. In our conventional soils, we use tillage very commonly which is hyper-disruptive for fungi but not bacteria. This is due to the structure of their bodies, the hairlike fungi break easily when tilled but the single-celled bacteria survive. The result is that most soils are deficient in fungi but abundant in bacteria which skews the soil ecosystem out of balance.
Protozoa
Protozoa are another important group of soil microorganisms that play a critical role in nutrient cycling what the bacteria consumed back into plant-available nutrients. They do this by consuming bacteria rapidly which stores excessive nutrients in their systems which are excreted back into the soil space. This excreted material is a perfectly balanced food source for your plants and is deposited right at the plant's root zone. These protozoa are consuming up to 10 000 bacteria every day which is a calculable amount of essential plant nutrients that you do not have to apply as fertiliser. This is one of the key benefits of living soil, nutrient cycling which means lower the need for fertiliser and decreasing the cost of production. This means that farming with living soil is a cost-effective way to produce food.
Nematodes
Nematodes are the largest microorganism group of the soil food web that play an important role in soil health. They are divided into two main groups that can be either beneficial or detrimental, depending on the species. Beneficial nematodes perform a range of important functions in the soil such as; feeding on pests, controlling populations of harmful insects, increasing nutrient cycling and arranging soil structure. Many of the harmful pests that damage crops start their lifecycle in the soil before emerging from the soil to find a host plant. An example of this is the Olive Fruit Fly (Bactrocera oleae) which causes significant crop damage to the leaves of olive trees. A number of nematode species, most notably Steinernema Feltiae feed on the larval stages of these flies which inhabits their life cycles and decreases their overall population. There are many examples of this across a range of pests. These are natural biocontrols at work in nature. Consider a natural forest ecosystem, the plants growing there are not diseased and covered with many pests are they? This is because these bio-controls are occurring continually in a natural ecosystem. As with all organism groups, there are species which cause damage to plants. Associated with root damage, decreased plant health and often crop loss these root-feeding nematodes can cause significant damage. The management of root-feeding nematodes is currently a large expense for much of the fruit and wine industry. The larger and dominant predatory nematodes prey on the small root feeders but these predatory species only occur in well-managed living soil.
The living soil ecosystem
The soil food web is a complex and dynamic ecosystem that is sensitive to disturbances. All of these microorganisms play a critical role in maintaining the right balance in the soil but are largely dependent on plants to survive. Root exudates are compounds released by the roots of living plants to stimulate the microbial community in the soil. This is done because the plant needs the range of benefits that the microbes can provide to the plant. Without this continual release of exudates into the soil many of these microbes die out, this is because they are completely dependent on the exudates to survive. That is why we follow the 5 principles of soil health to ensure these microbes are constantly active, thus the name Living Soil.
The benefits of living soil.
When we have highly active living soil which is matched the crops we want to cultivate the challenges of conventional farming diminish. For more in-depth information on each of the below points be sure to read my other blog post on Regenerative farming.
Reduced costs on fertilisers because the soil supports the plant throughout the season as the nutrient cycling process is constantly occurring.
Reduced cost on pest/disease control as the soil's natural pest/disease suppression is controlling the unwanted organisms.
Improving crop nutrient density through different plant nutritional pathways and processes occurring when compared to conventional cultivation.
Reduced tillage means less time working the land and lower fuel costs when using machinery.
Improved profit margins as organically certified cultivation are aligned with living practices.
Minimised environmental damage caused by the current conventional farming model.
Resulting in improvements in human health due to food that is more nutritious and contains less harmful residues from pesticides, fertilisers or fungicides.
It is important to note that applications of synthetic fertilizers, pesticides, fungicides, nematicides and herbicides can disrupt the normal function of the soil food web. The process of tillage is a huge disruption to the soil ecosystem and should be limited as much as possible. Any compaction of the soil through heavy machinery can lead to a distribution. Along with other practices that drastically change the soil environment results in an imbalance of the populations of beneficial microorganisms.
To learn more about the symbiotic relationship between plants and soil microorganisms I have written an E-Book that dives into all the details. Learn how to create a healthy and productive soil ecosystem that allows you to grow crops organically. I recommend looking out for my book "A Guide to Living Soil and Composting" written by Wesley Soule. Additionally, my business, SoilScopes offers soil testing services that can help you understand the unique characteristics of your soil and determine if your soil microorganisms can support your desired crops.
