I used to think that soil was just another word for dirt. I knew it was where plants grew, and thanks to my childhood in the countryside I knew it was also home for earthworms, ants, centipedes and so on. But mostly it just made me muddy. I couldn’t have even begun to imagine the amazingly complex ecosystem which, it turns out, exists within and makes up the soil. And I’m not the only one. Scientists have only recently got an idea of just how diverse the soil community is – just one teaspoon of good soil contains over one billion microorganisms, including 20,000 – 30,000 different species of bacteria and several metres of fungi. Its quite literally the foundation of all life on earth and its finally starting to get the attention it deserves. The UK Government has even put it front and centre of its new Agricultural Bill [source].
In this post I will discuss the awe-inspiring natural processes taking place under our feet, and how the fertilisers, herbicides, pesticides, insecticides and fungicides used on 93% of Europe’s farmland is disrupting them.
The soil food web
The soil food web is an interconnected, interdependent, changing and evolving entity. The majority of life in the soil is microscopic single celled organisms such as bacteria and protozoa. These organisms are constantly eating, growing, reproducing and dying. When they die they become food for slightly bigger organisms, and so on until birds and animals have a food source. In turn their waste products, and finally their dead bodies, feed the smaller members of the soil food web, and so it continues.
There is far more to it than just this, though. There are some wonderful symbiotic relationships between plants and soil microorganisms, mostly driven by the plant’s need for nutrients. Soil usually contains all the nutrients a plant needs, but often they’re some distance away and not in the soluble form a plant can take up. So the plant forms a relationship with the microorganisms. By secreting sugary substances called exudates through its roots, the plant feeds the microorganisms in return for delivery of nutrients. The most striking example of this relationship is with mycorrhizal fungi (yes, mushrooms!), whose reach effectively increases the surface area of the plant partner by up to 100 times. Mycorrhizal fungi deliver a wide range of nutrients to plants, including nitrogen, phosphorus, calcium, iron, copper and zinc. Their large networks of hyphae (fungal strands) move nutrients from areas where resources are high to areas where resources are low, helping out seedlings and weaker plants and stopping others from overdosing on nutrients. They even form their own affiliations with phosphate-solubilising bacteria which work on rocks to make phosphorus available, in return for carbon ‘payment’ from the fungi. Phosphorus is one of the major nutrients needed for plant growth, and its concentration has been shown to increase up to four times in mycorrhizal plants (over 90% of plants form a mycorrhizal relationship [source]).
The soil community provides a whole host of other benefits to plants, including fixing insoluble nitrogen from the air and making it plant-available, storing nutrients, enhancing soil structure, controlling pests and even producing hormones plants need to grow well. Scientific evidence shows that plants are able to tailor their exudates to attract specific beneficial microorganisms according to their nutrient or defence needs – a level of intelligence we cannot hope to be able to replicate with the less tailored nutrition profile of synthetic fertilisers. In an indication of how vital these relationships are to the plants, evidence indicates that they use up to 40% of the carbon they’ve made through photosynthesis on producing and secreting exudates.
The benefits of healthy soil do not stop there. Soil organisms decompose potential pollutants such as manure and even (up to a certain level) chemicals from agriculture or industry, preventing them from entering water sources. They also improve soil structure, increasing its water-holding capacity and reducing run-off which helps with both flood and drought prevention.
Even if you don’t agree that the incredible species diversity in the soil is in and of itself worth preserving, I hope its clear by now that the services provided by the soil community are vital to life on earth. So how is soil life impacted by the chemicals used by non-organic farms?
Broadly speaking, agrochemicals can be divided into two main categories. The first are to control weeds, pests and diseases. This category includes pesticides, herbicides, fungicides and insecticides (the ‘-icides’). The second category – fertilisers – provides extra nutrients to help plants grow.
The ‘-icides’ are designed to kill that which is perceived to be a threat to the crop. However, evidence shows that as little as 0.1% of the pesticides reach their target pests. The rest moves into the environment, usually killing non-intended species. The harm caused to bees by widely-used insecticide neonicotinoids has received widespread attention in recent years, leading to an EU ban in 2018. It is more difficult to invoke public empathy towards microscopic organisms, but the science shows that pesticides decrease total microbial biomass in the soil [source] as well as reducing the abundance and diversity of organisms [source].
A healthy soil food web depends on the functionality of all its parts – if there is a gap then the system breaks down and stops functioning properly. This often means more susceptibility to pests and diseases, since the soil has lost its ability to self-regulate (by, for example, crowding in such numbers around plant roots so as to not allow pathogens to take hold). This often leads to a vicious cycle of even more application of chemicals to treat the new pest or disease, and so on. One example of how chemical control can make things harder for farmers or land managers comes from the honey fungus, which is a significant challenge in forestry in particular. Increasing numbers of scientists are concluding that fungicides don’t work, which is at least partly because they also kill beneficial fungi, the most effective method of controlling the outbreak.
The second category of agrochemicals – fertilisers – doesn’t fare much better when it comes to unintended side effects. Fertilisers introduce a flood of soluble nutrients to the plant or the soil close to it. This alters the amount and nature of exudates produced by the plant, meaning the plant can be less receptive to affiliations with beneficial mycorrhizal fungi and other organisms. This in turn means that the plants are less healthy since they have been unable to meet their exact micro-nutrient needs. As well as leading to a higher risk of plant disease, this means our food contains fewer nutrients, with likely impacts on human health
Fertilizers also decrease soil aggregates (soil particles that stick together), which means the soil’s water-holding capacity is decreased and water run-off is increased. Finally, there is research to suggest that high nitrogen inputs destroys carbon in the soil, leading to a release of CO2 into the atmosphere as opposed to the carbon sequestration which happens in a healthy system.
Its not only the microorganisms which suffer at the hands of chemicals. They also seriously adversely affect the survival and reproduction of earthworms, much-loved friends of farmers due to their impacts on nutrient cycling and soil structure. A recent global metaanalysis found that synthetic fertilisers and pesticides are major contributory factors to plumetting insect numbers – with 40% of the world’s insect species now at risk of extinction. Fertiliser run-off causes harm to, amongst other things, aquatic life by encouraging growth of plankton and other aquatic plants which, when they die, decompose and consume all the oxygen that fish and crustaceans need to survive [source].
Conventional (aka chemical) farming is a system which has been willfully ignorant of natural processes in its quest for high yields. But we now have more knowledge than ever before of the complex workings of the natural world in creating a perfectly balanced system. The soil food web, with its many symbiotic relationships, is a perfect example. It is a natural phenomenon of which we have woefully underestimated the importance, and about which we still know remarkably little. We do, however, know enough to conclude that we should be doing everything in our power to protect and restore it.
Before agrochemicals came along in the 1960’s nature had developed a perfect system for growing plants in a healthy, harmonious ecosystem. Regenerative agriculture seeks to grow food in a way which restores these natural processes, focussing particularly on the soil since it is from this all other life begins. The future envisaged by regenerative agriculture is one in which nature is allowed to work in its beautifully harmonious way and ecosystems are in balance. This will mean that pests will be kept in check and healthy plants will have their own defences against disease. This is a future I’m proud and excited to be a part of.