Working with Underground Soil Ecology in Organic Farming


L. Acuña Sandoval


All anyone has to do is read the latest report from the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) to comprehend the grim details of our shifting planet. One of the worst predicted impacts in the coming decades (besides rising sea levels) is that food may become scarce. Food crops may not be able to survive or evolve fast enough in the changing climate to feed Earth’s inhabitants. How do we initiate changes now to be able to produce food to save future generations? A relationship that plants, humans and other species have with an ancient species of earth may hold the answer.


Fungi have been on Earth for more than 400 million years, with the first evidence of coexistence in Devonian-era land plants. Fungi are present in most soil and more than 80 percent of plant species have the ability to cooperate with them. Plants may not have been able to make the important terrestrial jump out of water and develop roots if not for this relationship with fungi. The Earth’s atmosphere would have continued to be rich in carbon dioxide versus oxygen, and many species that depend on respiration, including humans, might not exist. Arbuscular fungi (AM-fungi) in the Glomeromycota phylum are found in plant roots’ “rhizosphere” and have a unique relationship with plants. AM-fungi in this system cooperate (symbiosis) with plant species similar to a market system. The plant will secrete secondary metabolites, which function as a signal to the fungi “knocking at the rhizosphere door” in the root area. Phosphorus supplied by AM-fungi and sugar supplied by plants fixed during photosynthesis are the currency. The nutrient exchange (which is biodirectional) is vital to each for survival and fuels evolution for both. Phosphorus is essential for plants for both root and shoot development; however in high-pH areas (above pH 7), it is not in a form that plants can readily use. If a plant will supply sugar it is producing during photosynthesis to the AM-fungi, the fungi, in turn, will supply phosphorus, and then the symbiosis is born. The symbiosis is very complex and, depending on conditions, fungi can sometimes “defect” to become pathogenic or less cooperative and attempt to obtain the sugar for free at the expense of the plant and its fitness. Ecosystems that have fungi and microbe diversity and thus healthy soil can be imagined as a giant adaptable entity that can take hard punches from the weather yet still remain standing. AM-fungi with plant interaction is a hot topic of study, but what does this have to do with creating a resilient farm, filtering carbon and other nutrients, or assisting plants to continue producing food in the future? Everything.


Understanding the environment that may increase plants and beneficial AM-fungi to participate in a symbiosis is key. Diversity of AM-fungi and plant species, low soil disturbance and minimal added inputs are vital for a healthy ecosystem. On the contrary, if you give a plant all the nutrients it requires, such as soluble phosphorus, it may weaken the plant’s response to a cooperative relationship with AM-fungi. Why would it cooperate if it receives all nutrients artificially from mineralized, added sources of nutrients? The likelihood of both fungi and plants participating with each other can shift because it depends on soil conditions, and the symbiosis may be strengthened or disappear altogether. Fungi also have the ability to adapt and evolve at a higher efficiency than plants can with environmental stresses such as drought because their responses can be much faster. The big concern with food crops is that they cannot adapt fast enough in the changing climate, but, with a partnership of fast-evolving AM-fungi or seed-borne endophytes, this may be overcome.


How does one create and maintain resiliency in an ecosystem and be able to produce food and quality seed at the same time? A long-term research project performed in central Europe, the bio-dynamic, bio-organic and conventional (DOC) study, compared variations of conventional and organic-based farm practices for 22 years to understand how these different practices impact the presence and type of fungi in the soil. Organic-based practices that used cover crops or manure-based inputs to enrich the soil yielded the highest diversity of fungi versus mineral fertilizers. Nutrient density studies of the crops in each treatment would be an important next step along with the impact to seed quality in the following generations.


On my own farm some of the practices that were incorporated included planting perennial cover-crop combinations to limit bare soil areas because the soil would otherwise be vulnerable to wind and erosion. Aged compost extracts or teas were used to inoculate the soil with diverse AM-fungi and bacteria. AM-fungi prefer legume-rich areas and bacteria populations are higher in grass-rich areas, so an initial plant inventory can be used to survey the soil microbe populations. A more definitive measure would be a fungi-to-bacteria (F:B) ratio. Cash crops are planted with “understory” legumes, and entire field areas are never cleared or burned so as to not destroy invertebrate habitat. With this protocol in the last few years, the farm ecosystem is healthier and food crops are vibrant, with little added fertilizer. The target crops also require less water because the living mulch can regulate and conserve water in the soil. How does it do this? Once established, AM-fungi have structures called mycelia (or hyphae webs) that are attached to roots but much smaller, and in 1 cubic meter of soil can be 20,000 km in length. The hyphae have the ability to mine water and nutrients from long distances and enhance the infiltration of water through soil. The system also allows plants to communicate with each other to receive warnings such as pathogen attacks, as hyphae can “fuse” when they recognize the same species of fungi.


How can fungi help save the world? Carbon sequestration by healthy soil has the ability to allocate atmospheric carbon dioxide (CO2) into “long-lived pools” that accumulate and amass it and, most importantly, stop it from being immediately reemitted. In real numbers soil has the potential to sequester Carbon generated from fossil fuel emissions by a staggering 0.4 to 1.2 gigatons of carbon per year, or 5 to 15 percent of total global fossil-fuel emissions. If green energy is also embraced as the IPCC report suggests, we may be able to achieve the 80 percent cut in fossil-fuel use needed to alleviate a future of catastrophes.


Think of AM-fungi as noble old souls that have been our loyal friends for a very long time and may save future generations from the brink of extinction. If we utilize AM-fungi to initiate meaningful changes to ecosystems, even in city rooftops and abandoned fields, who knows what might happen? The dark mysterious earth may feed and sustain us and other inhabitants, instead of metaphorically shaking us off its back like a bunch of fleas with no remorse or negotiation, just natural selection.



Loretta Sandoval, a former analytical chemist, is an organic farmer and seed conservationist from Dixon, NM. She is a vendor at the Santa Fe Farmers’ Market, where she sells food products and locally adapted seeds. For more information regarding this article, email or