Here are my highly personal notes on Chapter Eleven: Soil — The Real Dirt in Peter Bane’s The Permaculture Handbook (2012). Any misrepresentations of Bane’s words or work are mine alone and completely unintentional. Notes on each chapter linked here.
This chapter is long and very detailed concerning soil science. And guess what? Today is World Soil Day! Listen to this great 1A radio program on soil health, titled “The Ground Beneath Our Feet,” that aired yesterday, especially to Oklahoma farmer Jimmy Emmons, who changed his mind and changed his entire way of farming.
“The soil is an animal which is everywhere a mouth.” — Emilia Hazelip
Soil is the most changeable of all elements in agriculture. The living organisms in the top foot of soil may equal 11 tons/acre. “Soils are created from an interaction of energy (chiefly from the climate and living organisms which transform it into action) with resistance, expressed as a function of geology — or parent rocks — and the resulting landforms that they reveal over time. The weathering of rock creates habitat for soil organisms at the same time that it grinds minerals into finer and finer particles which can be eaten by plants and microbes, and even by small soil animals.”
Soil is not solid. It’s filled with “the action of plant roots, fungal hyphae and burrowing animals which distribute living and dead organic matter from the surface to deeper layers, pull minerals from parent rock, and open channels for air and water to circulate. Small soil animals, searching for food, consume dead plant and animal tissue and excrete pellets, casts, frass and other manures which bind bits of inorganic material with organic waste and digestive secretions to form colloids. Earthworms are particularly effective and powerful in this way, leaving behind them not only burrows that become channels for air and water, but nearly perfect packets of plant food in the form of their castings.”
Layers of soil, top to bottom:
The Organic Layer covers soil, breaks the fall of raindrops, and prevents erosion. It also provides food for lots of foraging animals.
Just below this layer is the Accumulating Layer (“A”), “the topsoil horizon of conventional soil science,” where “organic residues of decomposition accumulate.” It has the largest percentage of carbon of any soil layer, and in temperate zones, there can be up to 20% organic matter in this layer.
Below this, the Elluviation Layer, where “minerals are being leached by the percolation of water.” Tilling soil mixes the Accumulating and the Elluviation layers.
Below this, the Banking Layer (“B”), sometimes called the subsoil, traps some leached minerals. Levels of organic matter are low here.
Below this upper subsoil is the Chemical Layer (“C”) “of broken and weathered rock.”
Next, the Durable Layer (“D”), or bedrock, which is not necessarily solid; it can be “fractured and permeable” due to chemical composition or seismic activity.
Ninety-seven percent of the bodies of animals, plants, microbes are made up of four elements: Hydrogen, Oxygen, Carbon, and Nitrogen. All occur as gasses and are cycled through the atmosphere, freely available. The remaining 3% consists of Phosphorous, Potassium, Calcium, Sulfur, Magnesium, and trace minerals, and these are the limiting factors in plant and animal growth and health. So the focus in soil repair is the minerals: healthy ecosystems retain them.
In temperate climates (not in tropical), “soil is built by the development of durable carbon in the form of humus, long-chain molecules created out of biomass by living organisms in the soil. … So building soil fertility in cool regions means adding organic matter to soil from the top down as mulch.”
Bacteria: the most common organism in soil; one teaspoon contains millions of them. Aerobic (flourish with oxygen) and Anaerobic (flourish without oxygen). Anaerobic bacteria evolved before photosynthesis and an oxygen-rich atmosphere. All the bacteria that consume dead organic matter are aerobic, but if they lack O2 for a bit, they just slow their metabolism and stop eating.
The Oxygen-Ethylene Cycle: This is a complicated little bit of agronomy and if it interests you in detail, please read the chapter or study the diagrams below.
Briefly, this is all about how gasses produced as anaerobic bacteria feed (ethylene and ammonium nitrogen) can cause nitrogen to dissolve and flow away, and when it does, iron (common and abundant in all soils), changes itself from ferric iron (red or rusty) to ferrous iron (black) by releasing an atom of oxygen into the now reduced atmosphere of the soil:
“This has tremendous implications for soil fertility and agriculture because it initiates the assimilating phase of soil nutrient transfer to plants. Ferrous iron reacts with a precursor found in leaf litter to convert it into ethylene gas, helping to further inactivate aerobic bacteria. Iron in its ferrous form also sheds its bonds to phosphate, sulfate and ions of trace minerals, dumping them unceremoniously into solution. And this new and rather promiscuous ferrous iron then forms bonds with particles of clay and organic matter. As it does so, ions of magnesium, calcium, potassium and ammonium which had been occupying those sites are displaced, also into solution. The highest concentration of this activity is in the rhizosphere or tiny envelope of water surrounding the root hairs of plants. Thus, as soil microsite conditions change from aerobic to anaerobic, all the plant nutrients — nitrogen, phosphorus, potassium, sulfur, calcium, magnesium and trace minerals, which had until then been held tightly to soil particles — enter into solution and can in that form be taken up by plant roots. This does not occur when the soil is constantly aerobic, nor does it occur when nitrate nitrogen — the form typically applied as chemical fertilizer — is present in large quantities. So industrial farming, by tilling soil and applying nitrate fertilizer, is preventing normal processes of soil nutrient assimilation by plants.
“In turn, plants feed soil organisms at their roots in order to enhance water and nutrient uptake and also to stimulate respiration by aerobic bacteria which cyclically exhaust oxygen in the rhizosphere, initiating anaerobic conditions, the production of ethylene gas and nutrient assimilation. This entire process is cyclic, a rocking back and forth at millions of microsites throughout a healthy soil between aerobic and anaerobic conditions, between digestion and assimilation. Both phases are necessary for dead matter to be consumed by microbes and resurrected by living plants. Conventional agronomy fails in every way to respect this normal and natural process.”
Taking the Measure of Soil:
Soil texture: gritty, spongy, buttery, smooth, sticky.
Soil series: names (e.g., Haworth, Bartholomew, Niagara) associated with soils of a distinctive texture in a given locale. (USDA)
Soil structure: platey, prismatic, blocky or granular in a continuum from compaction to good tilth. Healthy soils are more granular (larger clods)
Organic matter: living and dead organisms and their residues.
Soil pH (percent Hydrogen): measures acidity and alkalinity in soil on scale from 1-14, where 3 is acidic like lemon juice, 7 is neutral, and anything above 9 makes plant life difficult. Good garden soil is 6-7 pH. All soils approach neutral when organic matter is added.
Mineral Composition and Balance: Nitrogen (N), Phosphorus (P), and Potassium (K) are the nutrients most heavily used, but calcium (Ca), Magnesium (Mg), and Sulfur (S) are also important and lack of them can limit growth. Trace elements, as many as 40 of them, are also needed; these all occur in the human body and have some metabolic function: Zinc (Zn), Manganese (Mn), Copper (Cu), Boron (B), Iron (Fe), Molybednum (Mo), Cobalt (Co), Chlorine (Cl), Iodine (I), Sodium (Na), Chromium (Cr), Flourine (F), Selenium (Se), Vanadian (V), Germanium (Ge), and Silver (Ag).
Environmental Analysis: Assessing mineral balance in soil.
1. Is the soil likely to be acidic or alkaline? Depends on geology and geography.
2. Is the soil old or new? (in geologic time)
3. What is the soil’s texture? Clay (which has a huge surface area and a strong electrical charge) holds minerals more than sandy or silty soil.
4.Does pollution affect your soil’s pH? E.g., Tennessee and Ohio valleys and New England are major downwind areas for coal emissions from the Midwest (coal makes soil acidic).
5. Has the land been farmed chemically? (and thus been depleted of organic matter)
6. Is there heavy metal contamination, historically or currently? Especially in older urban areas and any place near former salvage yards, tanneries, chemical plants, gas stations, metal plating and wood treatment facilities; lead was not removed from paint and gas until 1976 and soils nearby may contain lead. Also soils near roads and highways more than 35 yrs old. Also cadmium (tire abrasion), mercury and arsenic (coal), radioactive isotopes (around the 108 commercial nuclear reactors in the U.S., with a dozen sites seriously contaminated)
7. What plants are growing in the soil? Some plants indicate what’s in the soil. Nettles like rich loamy soil, rhododendron and mountain laurel like highly leached, acidic soil.
8. How well are the plants growing? Plants with deformities, yellowing leaves, lots of pests, poor flowering and fruiting indicate mineral deficiencies. Brix reeadings (measures level of sugar in plant tissues) can indicate mineral nutrition in soil.
Repairing and Rebuilding Soil:
Add organic matter! It “increases food for soil microbes that create humus [which increases] the carbon content of soils increases their water- and
mineral-holding capacities.” Add it in two ways: by growing plants, “which put their roots down into the soil layers where they introduce photosynthates or sugary and starchy root exudates to feed soil microbes, and where these roots regularly die and are sloughed off to decompose.” Also lay green and brown vegetative material (as compost or chop & drop or however) on the soil surface so fungi and soil creatures can incorporate it into the soil layers: “The soil’s mouth is at the surface, not 3, 6 or 10 inches down. Plowing to incorporate plant residues is not unlike forcing unchewed food down someone’s throat with the notion that this will help them to eat.”
Keep a mulch cover on the soil at all times to protect soil from erosion by wind and rain, to protect soil organisms from drying, to conserve soil moisture, and to feed the soil.
Bane discusses the work of P.A. Yeomans and his Keyline system, developed in the 1930s and 40s. Involves dams and furrows, and if you’re interested, read the book.
He also talks at length about swales (ditches dug on contour), water bars (berms to divert water), pits and ponds, terraces — collectively, small earth works. Again, read the book if this interests you.
Crop rotation – rotate crops that bear from different parts (root, leaf, fruit, seed).
Grow cover crops (long list on pp. 209-210. (Below, buckwheat grown as cover crop in Windsor, Vermont, Oct. 2016)
Grow cold-hardy fertility crops (vetch, turnips, mustard) in winter to restore fertility.
Intercrop, e.g., strips of legumes between strips of grain.
Grow perennial crops in islands at end or edge of garden beds. (Below, some of the perennials I grow in and alongside my main vegetable bed, including echinacea, blueberries, elderberries, asclepias, and perovskia.)
Chop & drop mulch. Mulch with cardboard, newspapers, junk mail, wood chips, straw bales, animal manure, cocoa hulls, peanut hulls, pine straw.
Compost is not a panacea for soil repair or maintenance, but useful; make it with ratio of 20-30:1 brown or dead material to green or manure (highly nitrogen-rich material) and keep it moist.
Mineral and microbial amendments, like lime (calcium carbonate), wood ash (for potassium, alkalinity, Ca, P; don’t just pile it on soil but treat it like salt and sprinkle lightly), urine, rock phosphate (promotes fruiting and flowering), seaweeds, fish emulsions, etc.
Mycorrhizal fungi: Bacteria dominate alkaline soil (and produce more of it; fungi dominate acidic soil, humus-rich soil that’s not disturbed or tilled. The hyphae (feeding strands) of fungi can be very long, so fungi can mobilize nutrients over a broad area (but the hyphae are also very vulnerable to tillage and agrichemicals). Fungi also contain powerful enzymes to break down substances like chitin (cellular coating of insect bodies), animal bones and sinews, and long-chain C-based molecules like petroleum and pesticides. Most importantly, fungi “develop relationships with plant roots and appear to be critical for plant nutrition. Plants only moved out of water and onto land some 400–460 million years ago, after aquatic plants developed symbiotic relationships with fungi. As many as 95% of all plants, possibly more, have root associations with fungi, called mycorrhizae. As they break down dead tissues, fungi take minerals, including nitrogen in the ammonium form, into their bodies and hold them, swapping them in trade with plant roots for sugars, or releasing the whole lot upon death.” To help fungi, don’t till or use chemicals in the garden. We can also grow our own fungi through a process called inoculation (mycorrhizal inoculants can be purchased commercially).
Featured image (top image) is an earthworm and beetle in my yard, June 2014.