I Went to School for Agriculture and Everything They Taught Me About Soil Was Wrong
It wasn’t long ago that I was sitting in a college soil science course at my alma mater land grant university. If I had just a penny for every time the phrases “soil test”, “law of the minimum” and “NPK” were repeated, I would be a very wealthy farmer by now.
We spent almost the entire semester listening to a conventionally-trained soil professor talk in circles about chemistry soil panels and synthetic mineral products that supposedly “need” to be added to the soil for crop success. They literally told us the that plants could not grow without them.
Evidently, the university was making a lot of money teaching the conventional paradigm of NPK (Nitrogen, Phosphorus, Potassium) agriculture fueled by fertilizer and pesticide corporations. They basically said the soil was dead and just acted as a passive material through which fertilizers and water could flow.
Our homework involved meticulous calculations of how many pounds of fertilizer to add to a figurative field crop scenario. We covered the nitrogen, phosphorous, and potassium cycles extensively, yet the professor never once even mentioned the microbiology that fuels these cycles, along with every other natural cycle on Earth (Van Keulen 2015).
Universities & Big Ag Still Stuck in the (old) Soil Chemistry Paradigm
We’ve known for years that microorganisms are absolutely essential for healthy soil. Cutting-edge microbiologists like Dr. Elaine Ingham have been researching soil bugs and microbes for nearly a decade, but mainstream universities have been quite slow to catch up.
You see, agriculture has been dominated by a chemical idea of soil for the last century. Both conventional farmers and scientists have long looked at soil as an inert, dead medium that’s just a place for plant roots to anchor and uptake the fertilizers produced by agribusiness companies.
Ironically, their perspective perfectly defines dirt, which is what soil becomes after it is degraded and stripped of all life. Though this paradigm acknowledges there are earthworms and other tiny little bugs in the soil, they continue to pay little attention to them.
In fact, most “soil experts” of recent decades have just dismissed soil organisms as unimportant to plants or agriculture. Why would they focus on a bunch of tiny bacteria and fungi when the research dollars are funneled toward developing new fertilizers to make faster-growing, higher-yielding crops? Fertilizer sales amounted to $23.5 billion in 2016 in the U.S. alone, so you can see why that school of thought has remained the dominant one.
Now that is all changing. The microscope was invented in 1590, however soil scientists and farmers are only recently starting to make full use of this tool. With increased gene sequencing technology and the exploding interest in the human microbiome (the billions of microbes in your gut and every surface of your body), the microscopic little organisms in the ground beneath our feet are finally reaching the forefront of agricultural research.
Soil microorganisms, abbreviated “microbes”, are the driving force of plant life on Earth. They act as the digestive system of plants by converting their food (minerals) into forms that plants can consume (Van Keulen 2015). In other words, microbes create what we call “fertility” in the soil.
Below-Ground Ecosystems Make Nature’s Original Fertilizers
Just like a forest or grassland, there are incredibly complex ecosystems below ground. Bacteria, fungi, nematodes, and protozoa are the key players in this underground economy
However, everything from earthworms and spiders to voles and groundhogs play an important role in soil ecology. Together, they all create a profoundly diverse and complex soil food web. Dr. Elaine Ingham discovered and diagrammed this soil food web nearly 4 decades ago, however her research is just recently coming to the forefront of biological agriculture.
If you take a look at an old growth forest, you can see this dynamic soil food web cycling happening right before your eyes. Trees that are hundreds of years old and hundreds of feet tall are growing from soil that has never ever had fertilizer applied to it. How is that possible? Where are the trees getting all their nutrients?
It’s certainly not just manure. Sure, an occasional deer or squirrel will hop through the woods and poop on the ground, but that wouldn’t add up to enough nitrogen or any other nutrient for a tree to grow so massive.
What about the decaying leaves, pine needles, and other dead stuff accumulating on top of the soil? Yes, of course the decomposing materials are feeding the plants. But what is breaking them down and transforming them into plant food?
It’s all about the Soil Microbes!
Billions and billions of them work tirelessly all day every day to transform dead plant and animal materials, as well as rock minerals, into soil organic matter and plant food. Soil itself is formed by microorganisms eating away at rocks, and with the help of water, dissolving minerals into plant-available forms.
Lichens and hardy pioneer plants are the first to colonize the stone, eventually giving way to herbaceous plants and shrubs. Slowly over geological time, microbes and their plant allies build layers, metamorphosing bare rock into rich soil.
They simultaneously change atmospheric elements into plant food, as in the case of nitrogen fixation by bacteria called Rhizobium that live in the root nodules of legumes. These Rhizobia have a symbiotic relationship with plants that allows them to transform atmospheric nitrogen (N2) to ammonium by utilizing plant root exudates.
This biological fixation of nitrogen provides the bulk of nitrogen to agricultural soils, even in arid regions (Zahran 1999). Studies have demonstrated that microbiological inoculants reduce fertilizer use (Adesemoye 2009). It is clear that we need to be paying more attention to microbial mediation of soil nutrients.
Nutrient Mineralization: Microbes as the Plant’s Digestive System
Scientific studies also have found that protozoa and nematodes act as biological grazers that facilitate mineralization of plant nutrients. Mineralization is just a fancy word for breaking down a chemical compound.
Without getting too technical, this is basically the switch from an organic (carbon-containing molecule) to an inorganic compound. This mineralized compound is water-soluble so that plants can take it up. Keep in mind that, in chemistry, inorganic means the compound does not contain carbon (not to be confused with certified organic farming).
As protozoa and nematodes (two less-talked-about soil microbes) eat fungi and bacteria, they transform nitrogen and phosphorus into plant-available forms. Basically, they are eating microbes and extracting their nutrients, which can in turn feed plants.
You could compare the process to the way a cow eats grass, digests and processes those nutrients, and then make them available to humans when we consume an animal product (calm down vegans, this is just an example of nutrient transfer). Humans cannot readily access the nutrients in grass. The cow is the mediator between grass and human, in the same way that protozoa and nematodes are the mediators between minerals (plant food) and the plants.
So, plants need a middle-man because they cannot readily access the nutrients in rocks, organic matter, or the atmosphere. They are unavailable and need to be transformed, or mineralized. Microbes are the mediators, the middle-men. They are sort of like the plant’s external digestive system. They make clever swaps with plants that are mutually beneficial. Microbes get “cakes and cookies” called root exudates from their plant hosts. In turn, the plants send off their microbe allies to collect and mineralize the nutrients they need.
50% to 100% Decrease in Fertilizer Use with Soil Biology
When these microbes are present in the plant rhizosphere (the area around the roots), they increase nitrogen uptake, increase plant growth, and support faster initial growth of plant roots without any synthetic fertilizers needed (Ingham 1985).
Even in conventional systems (where most microbes have likely been killed by herbicides, fungicides, and tillage), these processes can quickly be revitalized. One study inoculated the soil of chili plots in India. They added only two microbes, Funneliformis mosseae (a myccorhizal fungus) and Bacillus sonorensis (a soil bacteria) and experimented with different levels of synthetic NPK fertilizers in different plots. They found a drastic 50% reduction in the need for NPK fertilizers in plots that were inoculated with the microbes (Thilagar 2016). They went on to conduct a large-scale field trial that validated their results.
Microbes are powerful! And soil microbiologists like Dr. Elaine Ingham have demonstrated that fertilizer costs can be cut by 100% — completely eliminated — simply by nurturing the complex below ground Soil Food Web. This is how Mother Nature has been growing plants without fertilizers for literally thousands and thousands of years, perhaps it’s time humans took note.
With modern dilemmas like fertilizer runoff and pollution, climate change, and reduced farm financial viability, one might wonder how we can work with microorganisms to reduce fertilizer use and boost plant nutrient uptake all while saving farmers money. A biological approach to soil management provides a promising solution.
Adesemoye, A.O., Torbert, H.A. & Kloepper, J.W. (2009) Plant Growth-Promoting Rhizobacteria Allow Reduced Application Rates of Chemical Fertilizers. Microb Ecol 58, 921–929. https://doi.org/10.1007/s00248-009-9531-y
Gro Intelligence. (2018) A Look at Fertilizer and Pesticide Use in the US. https://gro-intelligence.com/insights/articles/a-look-at-fertilizer-and-pesticide-use-in-the-us
Ingham, R.E., Trofymow, J.A., Ingham, E.R. and Coleman, D.C. (1985), Interactions of Bacteria, Fungi, and their Nematode Grazers: Effects on Nutrient Cycling and Plant Growth. Ecological Monographs, 55: 119–140. https://esajournals.onlinelibrary.wiley.com/doi/abs/10.2307/1942528
Thilagar G., Bagyaraj D.J., Rao M.S., (2016) Selected microbial consortia developed for chilly reduces application of chemical fertilizers by 50% under field conditions, Scientia Horticulturae, Volume 198, Pages 27–35, ISSN 0304–4238, https://doi.org/10.1016/j.scienta.2015.11.021.
Van Keulen, G., Hallin, I. (2015) Microbial Modulation of Soil Ecosystem Processes”. Microbiological Society: Soil. https://microbiologysociety.org/publication/past-issues/soil/article/microbial-modulation-of-soil-ecosystem-processes.html
Zahran, H. H. (1999) Rhizobium-Legume Symbiosis and Nitrogen Fixation under Severe Conditions and in an Arid Climate. Microbiology and Molecular Biology Reviews Dec 1999, 63 (4) 968–989. https://mmbr.asm.org/content/63/4/968.short