Over these last few months, attending various events in the UK and Ireland, I kept hearing references to the Oxford Real Farming Conference, and in particular, a keynote talk given by Dr. Elaine Ingham of Soil Foodweb Inc.
Remembering back to my school Biology classes, I was broadly aware of what the soil web was, but to be honest I had not considered the concept since then. The following graphic has been taken directly from Dr. Ingham’s slide pack & outlines the hierarchies of a simplified soil food web:
The crux of Dr. Ingham’s talk is that the typical modern approach to agriculture, in particular the application of ammonium nitrate fertilisers, has destroyed the microbiological organisms that usually cycle nutrients through the soil foodweb. With these organisms gone, we are unable to replenish nutrients in “plant available forms” from the soil mineralogy and are hence committed to adding increasing amounts of these artificial fertilisers year on year.
One of the major lessons I took away from the talk was that not all soil nutrients are in forms that plants can use. It is not simply enough to have high amounts of carbon, nitrogen, etc. in a soil. We also need microbiological processes to take place that transform these into plant available forms.
As plants photosynthesize, they release sugars, proteins and carbohydrates through their roots – “cakes and cookies”, as Dr. Ingham puts it. These exudates attract, and are fodder for, the fungi and bacteria of the first level of the food web. These in turn excrete acids and enzymes which solubilise nutrients from the surrounding soil particles and absorb them into their bodies. The nematodes & protozoa of the next level in the web then feed on these fungi and bacteria, and it is this digestive action that transforms these nutrients into plant available forms right at the root zone.
Like a lot of things on this voyage of permaculture discovery, most of these aha! moments are simply a realisation of common sense; this next one is no different. Dr. Ingham goes on to explain that plants & their processes have evolved over millennia to proliferate beneficial organisms where they require them. The presence of pests and disease indicates that something is out of balance with the system, as plants do not naturally profliferate “the bad guys”. Similarly, if soil biology is healthy, any organic detritus left on the surface of fields will be quickly broken down by these organisms and absorbed into the soil as available organic matter. “If you are still seeing recognisable material on the surface of your field weeks after harvest, it is nature’s way of trying to tell you that your soil microbiology is either unhealthy, or is not present.”
So, do we all need to become Microbiologists to get the best from our soils?
While Dr. Ingham does evangelise that people can and should take a microscopic approach to managing their soil microbiology, she also advocates pragmatism. In broad terms she explains that anaerobic organisms are the “bad guys”, the pests and source of disease. A side effect of anaerobic soil conditions is soil acidification, as Dr Ingham states, “there is no way to have a soil pH lower than 5.5 if aerobic conditions are maintained”. Further to this, in the acidic range, plant available forms of nitrogen, phosphorous and sulphur are lost from the soil in significant amounts through oxidation.
Benchmarking, monitoring and testing
Traditional soil test results will only tell you the mineral & nutrient content that is held within the sample in plant available forms. The results tell you nothing of the nutrients locked away in non-available forms within the soil mineralogy. Without the correct microbiology to liberate these minerals, all of this information is for naught.
Dr. Ingham goes on to say “There is not a single soil on this planet that lacks the nutrients to grow plants for the next 10,000 years; including extreme deserts and tundra”. The only true limitation at present is that often these nutrients are locked away in forms that are not accessible to plants. Hence, the real question should be “Do we have the correct biology (bacteria and fungi) to liberate nutrients from the soil aggregate?” and “Do we have the nematodes, protozoa and arthropods to release these nutrients back to the soil in plant available form?”
What does this mean for us here in Donegal?
Well, as if we didn’t know it already, water management is of the utmost importance. We can’t do anything to change the fact we get 2 metres of average annual rainfall, but with carefully designed landforms & Keyline systems to manage this abundance to prevent the crux of all anaerobic scenarios, waterlogged soil.
The power of observation should not be underestimated. Dr Ingham explains: “what would grow in your fields if you did nothing for one year? If the answer is weeds, then your microbiology is bacterially dominated”.
At the opposite end of the microbiological balance are the most resilient and self-managing ecosystems on Earth, Woodland habitat, whose microbiology is predominately fungal. Between these two extremes lie pasture and grasslands, where bacteria and fungi exist together as a balanced system.
Theory in action
So, the theory goes that with steps to correct water management & by inoculating fungi on a site, we can encourage land back to productive pasture whilst encouraging the microbiology that help support and regenerate the ecosystem.
We innoculate soil microbiota through the broadacre application of composts, but this will be the subject of a seperate post. Once I get my head around that particular issue…