Author:  Anna G. Aquino

Soil organic matter is vital to a healthy ecosystem and originates from decomposing remains of organic life. It has the unique ability to increase a sandy soil’s water-holding capacity while assisting a clayey soil to drain.  The subsequent improvement of soil structure reduces  erosion by increasing water infiltration.  Organic matter is the habitat for a vibrant soil food web whose inhabitants decompose it and provide nutrients for plants.  Fertility and nutrients reside in organic matter. We depend on soil microbes to detoxify pollutants. Soil is also the largest reservoir of carbon, containing more carbon than in the atmosphere and vegetation combined, thus instrumental in carbon sequestration. According to the Yale School of the Environment, soil degradation due to unsustainable land use has released billions of tons of carbon into the atmosphere, but carbon can be returned to the soil through organic and sustainable practices. (1) Civilizations throughout human history have declined and died as their soil has declined and died. (2) This is a sobering thought considering that the organic matter content of America’s soils has dropped dramatically, from as high as 10% to sometimes less than 1%.(3)  This reduction in organic content has resulted in a declining nutritional value of our food. (4)

Conventional landscape management with its dependence on synthetic fertilizers has all but forgotten that nature has a great system for providing soil fertility.  In a natural and undisturbed system, the soil food web organisms decompose organic matter, handing off the recycled nutrients back to plants.  In a forest, all manner of material is left to decay and cycle back to plants in nature’s perfect system; no one is raking (…blowing) it away, requiring the application of fertilizer. 

Nutrient Cycling in Soils, Source: UC Davis Global Soil Health Portal

Synthetic fertilizers have high volatility and solubility and can quickly dissolve and reach the water table and run-off to water bodies contributing to pollution.(5) Organic fertilizers and composts have lower nutrient analyses than synthetic, but since they are more stable and immobile, as soil microbes break them down to feed plants, the nutritional value can exceed that of synthetics.  Many have a broad spectrum of trace minerals, carbon, and beneficial organisms plus an abundance of energy.  We feed microbes by adding mulch which will compost over time, or by directly applying compost. The organisms in the soil do the work for us, providing nutrients to the plants.  This avoids creating a system dependent on applied chemicals which can cause microbes to go missing.  

Manufacturing a bag of fertilizer is energy intensive and emits heavy amounts of carbon dioxide into the atmosphere.(6)  The three primary elements in synthetic fertilizers are N-P-K. Nitrogen (N) requires a great deal of energy from fossil fuels to process, phosphorus (P) and potassium (K) are non-renewable mined resources, therefore not sustainable.  Synthetic fertilizers (and pesticides and herbicides) can harm and kill soil flora and fauna, destroying this complex web of life.  Life above ground suffers or dies, because the soil structure gradually deteriorates.  Worms burrow away from synthetic fertilizers and plants lose the benefits of their aeration and their castings.  The USDA study of earthworms and ammonium sulfate fertilizer demonstrated that all the earthworms in the study area were dead after three years. (7)  

The easiest way to restore soil health is with compost containing the full diversity of life. The soil food web (8) is a complex array of fungi, bacteria, worm castings, dead plants and animals, minerals, root exudates, and microbial life. We feed microbes with compost and they do the rest of the work breaking down the compost into available nutrients. If compaction is an issue, forking-in or injecting the compost at the depths of compaction will be necessary until a good soil structure is built.  The initial soil building stage using organic compost can be more expensive than non-sustainable methods that use synthetic fertilizers.  As time passes, however, the soil in an organic system continually improves itself until no more intervention is necessary, in other words it becomes self-sustaining. In contrast, the application of chemical fertilizers and pesticides threatens the health of the soil biology resulting in a dependency on continuous applications. (9)

Microbiologist Elaine Ingham claims that if every farm and garden switched from synthetic chemical management to organic and sustainable management, we could restore depleted soils by instilling back microbes, subsequently sequestering sufficient atmospheric carbon to reverse climate change. (10) Plant materials decay and support microbes including fungi. Spaghetti-like strands of fungal hyphae are mostly made of carbon and thus are a major way atmospheric carbon, the primary greenhouse gas, is stored in the soil. This is carbon sequestration. The fungal hyphae get thicker and thicker storing more and more carbon. Mycorrhizal fungi, when in symbiosis with tree roots, can increase the effective surface area for acquiring nutrients and moisture an amazing 1000 times.  The fungi profit from the exudates provided by the trees, using that energy to push through the soil.  As mentioned earlier, Phosphorus is a non-renewable mineral resource contained in N-P-K synthetic fertilizers.  Fungal acids can mine and unlock tied-up phosphorus, retrieving it for plants, another example of how important soil microorganisms are to sustainable landscape management.(11) Some fungal specimens are spectacular; the largest organism in the world is a fungus, Armillaria, aka Humongous Fungus. It is in Oregon, sometimes underground and sometimes revealing itself above ground, is thousands of years old, and is the size of 1665 football fields. As we lose our organic topsoil through ill-advised land use practices, the amount of carbon storage is declining, and the necessity for building healthy topsoil increases.   

The renowned horticulturist and educator Tony Avent, proprietor of Plant Delights Nursery in Raleigh, NC has said “We don’t want to put particulates and chemicals in our waterways.  We have to learn to garden more sustainably for us, for our neighbors, for the environment.  And it is far less work.  You can pay me now or pay me later.  You are much better off doing it right initially.”

To improve the soil quality of the gardens in our care, Capital Trees:

• Has discontinued the spraying of synthetic fertilizers, herbicides, and pesticides
• Uses compost to amend the garden soil as needed
• Does periodic soil testing
• Leaves plant debris in beds to be decomposed by soil organisms, “A messy garden is a healthy garden.” D. Tallamy
• Has eliminated bark mulch in established gardens, using leaves, composted leaves, or “native” mulch (arborist’s chippings of entire removed plants that mimic forest floor, more on this in a future blog)

As we continue to amend and improve the soil of our gardens, we will bring back the natural balance and yield healthier plants. We will share what we learn, our challenges, and new practices we are implementing.

(1) Soil as Carbon Storehouse: New Weapon in Climate Fight? https://e360.yale.edu/features/soil_as_carbon_storehouse_new_weapon_in_climate_fight

(2) Wits University. (2013, November 4). Civilizations rise and fall on the quality of their soil. ScienceDaily. Retrieved March 21, 2022 from www.sciencedaily.com/releases/2013/11/131104035245.htm;

(3) Can American soil be brought back to life? Jenny Hopkinson, Politico,  09/13/2017; https://www.politico.com/agenda/story/2017/09/13/soil-health-agriculture-trend-usda-000513/; Building Soils for Better Crops/Ch 2. What Is Organic Matter and Why Is It So Important/SARE Outreach/Fred Magdoff, Harold van Es | 2021 | https://www.sare.org/publications/building-soils-for-better-crops/what-is-organic-matter-and-why-is-it-so-important/#Plant-Nutrition

(4) Dirt Poor:  Have Fruits and Vegetables Become Less Nutritious? https://www.scientificamerican.com/article/soil-depletion-and-nutrition-loss/

(5)  How Chemical Fertilizers Cause Water Pollution https://www.conserve-energy-future.com/how-chemical-fertilizers-cause-water-pollution.php

(6) Fertilizer Life Cycle Perspective https://www.yara.com/crop-nutrition/why-fertilizer/environment/fertilizer-life-cycle/

(7) USDA Agricultural Management Effects on Earthworm Populations; https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_053291.pdf; PennState Extension, Why are Earthworms Important? https://extension.psu.edu/earthworms

(8) Learn more about the soil, food, web here;  https://www.soilfoodweb.com/resources/animations-videos/?vID=372925873%3Fh%3D707aa77aa3

(9) The effects of chemical and organic fertilizer usage on rhizosphere soil in tea orchards https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6538140/

(10) Soil Carbon Sequestration, https://www.soilfoodweb.com/resources/animations-videos/?vID=372478833&h=7c10d53c26

(11) Teaming with Microbes, The Organic Gardener’s Guide to the Soil Food Web, Jeff Lowenfels & Wayne Lewis

(12) The Biggest Organism on Earth is a Fungus https://www.mushroomrevival.com/blogs/podcast/the-biggest-organism-on-earth-is-a-fungus

Nutrient cycling image source:  UC Davis Global Soil Health Portal; http://soilhealth.ucdavis.edu/soil-challenges/low-organic-matter, accessed 8/6/2022

Honey Fungus image source: https://commons.wikimedia.org/wiki/File:Honey_Fungus_%28Armillaria_mellea%29.jpg