The living portion of soil is made up of plant roots, and of the numerous microbes and other living organisms that improve soil structure by breaking down organic material.
The recently dead components include deceased soil organisms, green plant material and fresh manures. They decompose readily, and release nutrients quickly.
The very dead portion is humus, the final residue of organic matter breakdown that’s important for soil structure and disease suppression. For fertile soil, all three forms of organic matter should be present at all times. It's easy to get started to build, restore and grow soil!
In the simplest tradition of organic and natural methods, add a little mulch or compost, and you’re well on your way to make good soil for your homegrown vegetables. In the long run, success in your garden depends on making healthy garden soil. The more you can do to keep your soil healthy, the more productive your garden will be and the higher the quality of your crops…. or so they say, and we are about to find out on our one-acre farm… with the development of our very own crop farm! Some people start with a layer of newspaper or cardboard over a mowed area as a weed barrier.
Good soil care methods imitate natural soil communities. Here we include protecting soil structure, feeding the soil with nutrients from natural and local sources, and increasing the diversity and numbers of the microbes and other organisms that live in the soil.
How so we achieve these goals? Although there are many ways to do this, they all revolve around two basic concepts:
1. Add manures for nitrogen. All livestock manures can be valuable additions to soil — their nutrients are readily available to soil organisms and plants. In fact, manures make a greater contribution to soil aggregation than composts, which have already mostly decomposed.
You should apply manure with care. Although pathogens are less likely to be found in manures from homesteads and small farms than those from large confinement livestock operations, you should allow three months between application and harvest of root crops or leafy vegetables such as lettuce and spinach to guard against contamination. (Tall crops such as corn and trellised tomatoes shouldn’t be prone to contamination.)
The Maryland Department of Agriculture (MDA) wants to see more farmers recycle manure instead of buy commercial fertilizer products, and the agency has launched a manure resource page to encourage using the natural plant food. Local farmers have welcomed the new resource the MDA refers to as “Manure Happens.”
2. Try compost. Compost is a means of recycling almost any organic wastes. It reduces the bulk of organic materials, stabilizes their more volatile and soluble nutrients, and speeds up the formation of soil humus. Regular applications of modest amounts of compost — one-quarter inch per season — will provide slow-release nutrients, which will dramatically improve your soil’s water retention and help suppress disease. We recommend using only vegetable matter if you decide to try building a compost heap yourself.
3. Mine” soil nutrients with deep rooted plants. When you first start gardening, it may be necessary to use rock dust, bio-char (ashes from a wood stove) and other slow-release sources of minerals, to correct mineral deficiencies in the soil. In the long run, however, you can supply minerals without purchasing inputs. The organic materials we add to our soil supply most of the minerals healthy crops need. In addition, we can plant “fertility patches” to grow a lot of our own mineral supplements.
Fertility patches include plants that function as “dynamic accumulators.” That is, their roots grow deep, and “mine” mineral reserves from the deeper layers of subsoil, where it has weathered out of the parent rock. The roots of comfrey, for instance, can grow 8 to 10 feet into the subsoil. Stinging nettle is another extremely useful dynamic accumulator. Both nettle and comfrey, in addition to high mineral content, are high in nitrogen. They make excellent additions to a compost heap or can be used as mulches.
4. Plant cover crops. Growing cover crops is perhaps the most valuable strategy we can adopt to feed our soil, build up its fertility and improve its structure with each passing season. Freshly killed cover crops provide readily available nutrients for our soil microbe friends and hence for food crop plants. Additionally, the channels opened up by the decaying roots of cover crops permit oxygen and water to penetrate the soil.
Legumes (clovers, alfalfa, beans and peas) are especially valuable cover crops, because they fix nitrogen from the atmosphere into forms available to crop plants. Mixes of different cover crops are often beneficial. For example, in mixes of grasses and clovers, the grasses add a large amount of biomass and improve soil structure because of the size and complexity of their root systems, and the legumes add nitrogen to help break down the relatively carbon-rich grass roots quickly.
5. Cover the soil with mulch. An obvious way to keep the soil covered is to use organic mulches. Some people advise against using high-carbon materials such as straw or leaves, since soil microbes “rob” available nitrogen from the soil in order to break down the excess amounts of carbon. This is only true, however, if we incorporate these high-carbon sources into the soil. I once tilled in some coarse compost containing large amounts of oak leaves not yet fully decomposed, and found that crops grew quite poorly there the entire season.
However, if high-carbon materials are laid down on top of soil as mulches, there won’t be any problem. The mulch retains soil moisture and protects against temperature extremes. Microbes, earthworms and other forms of soil life can “nibble” at the mulch, and slowly incorporate their residues into the topsoil. Actually, high-carbon mulches are preferable for weed control to materials that decompose readily, since they persist longer before being incorporated into the soil food web.
6. Use permanent beds and paths. A key strategy for protecting soil structure is to grow in wide permanent beds and restrict foot traffic to the pathways — thus avoiding compaction in the growing areas — and to plant as closely as possible in the beds. Close planting shades the soil surface, which benefits both soil life and plants by conserving moisture and moderating temperature extremes.
You also can use paths to grow your mulches, or mulch the paths and take advantage of foot traffic to help shred or grind materials such as straw or leaves. From time to time, this finely shredded material can be transferred to the beds, where it will break down much more readily than in its coarser forms.
7. Try low-tech tillage. There are almost always better alternatives to tillage, especially power tillage, which inverts and mixes the different layers in the soil profile, disrupts the soil food web and breaks down the “crumb” structure we have worked so hard to achieve. Even in the case of cover crops, which must give way to the planting of a harvest crop, it is not necessary to turn them into the soil, as usually recommended. Instead, consider these alternatives.
You can bury the cover crop under a heavy mulch to kill it. If the soil is in loose, friable condition, it is easy to pull the cover plants up by the roots and lay them on the bed as mulch. Certain plants such as rye and vetch are difficult to kill without tillage, but cutting them immediately above the crowns after seed stalks or flowers form will kill them. Use the upper ends of the plants as a mulch to help break down the roots more rapidly.
The only time to do massive tillage in the garden is when transplanting a sapling or digging root crops such as potatoes, sweet potatoes and burdock. With such crops, dig deep and thoroughly with the spading fork — the goal, however, is to make such intensive disruptions the rare exception rather than the rule. That way, the intact soil life communities in surrounding beds soon help rebuild the soil food web in the disturbed areas.
One of my Youtube mentors, Richard Perkins
By Jacques Leslie
Dec. 2, 2017
Leer en español
The last great hope of avoiding catastrophic climate change may lie in a substance so commonplace that we typically ignore it or else walk all over it: the soil beneath our feet.
The earth possesses five major pools of carbon. Of those pools, the atmosphere is already overloaded with the stuff; the oceans are turning acidic as they become saturated with it; the forests are diminishing; and underground fossil fuel reserves are being emptied. That leaves soil as the most likely repository for immense quantities of carbon.
Now scientists are documenting how sequestering carbon in soil can produce a double dividend: It reduces climate change by extracting carbon from the atmosphere, and it restores the health of degraded soil and increases agricultural yields. Many scientists and farmers believe the emerging understanding of soil’s role in climate stability and agricultural productivity will prompt a paradigm shift in agriculture, triggering the abandonment of conventional practices like tillage, crop residue removal, mono-cropping, excessive grazing and blanket use of chemical fertilizer and pesticide. Even cattle, usually considered climate change culprits because they belch at least 25 gallons of methane a day, are being studied as a potential part of the climate change solution because of their role in naturally fertilizing soil and cycling nutrients.
The climate change crisis is so far advanced that even drastically cutting greenhouse gas emissions won’t prevent a convulsive future by itself — the amount of greenhouse gases already in the atmosphere ensures dire trouble ahead. The most plausible way out is to combine emission cuts with “negative-emission” or “drawdown” technologies, which pull greenhouse gases out of the atmosphere and into the other pools. Most of these proposed technologies are forms of geoengineering, dubious bets on huge climate manipulations with a high likelihood of disastrous unintended consequences.
On the other hand, carbon sequestration in soil and vegetation is an effective way to pull carbon from the atmosphere that in some ways is the opposite of geoengineering. Instead of overcoming nature, it reinforces it, promoting the propagation of plant life to return carbon to the soil that was there in the first place — until destructive agricultural practices prompted its release into the atmosphere as carbon dioxide. That process started with the advent of agriculture about 10,000 years ago and accelerated over the last century as industrial farming and ranching rapidly expanded.
Among the advocates of so-called regenerative agriculture is the climate scientist and activist James Hansen, lead author of a paper published in July that calls for the adoption of “steps to improve soil fertility and increase its carbon content” to ward off “deleterious climate impacts.”
Rattan Lal, the director of the Carbon Management and Sequestration Center at Ohio State, estimates that soil has the potential to sequester carbon at a rate of between 0.9 and 2.6 gigatons per year. That’s a small part of the 10 gigatons a year of current carbon emissions, but it’s still significant. Somewhat reassuringly, some scientists believe the estimate is low.
“Putting the carbon back in soil is not only mitigating climate change, but also improving human health, productivity, food security, nutrition security, water quality, air quality — everything,” Mr. Lal told me over the phone. “It’s a win-win-win option.”
The techniques that regenerative farmers use vary with soil, climate and crop. They start from the understanding that healthy soil teems with more than a billion microorganisms per teaspoon and the behavior of those organisms facilitates hardy plant life. To fertilize their fields, regenerative farmers use nutrient-rich manure or compost, avoiding as much as possible chemical fertilizers and pesticides, which can kill huge quantities of organic matter and reduce plants’ resilience. They don’t like to till the soil, since tillage increases carbon emissions into the atmosphere. Some farmers combine livestock, cover crops and row crops sequentially on the same field, or plant perennials, shrubs and even trees along with row crops. Leaving soil bare during off-seasons is taboo, since barren soil easily erodes, depleting more carbon from the soil; regenerative farmers instead plant cover crops to capture more carbon and nitrogen from the atmosphere.
Until the advent of synthetics in the late 1800s, fertilizer consisted chiefly of carbon-rich manure or compost. But synthetic fertilizers contain no carbon, and as their use spread along with tillage practices to incorporate them, soil carbon content declined. The process accelerated after World War II, when America’s nitrogen-based munition plants were converted into nitrogen-based fertilizer factories. Most agricultural colleges still teach soil fertility chiefly as an exercise in applying inorganic chemical fertilizer, while overlooking soil’s biological role (and its carbon content). Despite soil’s connection to climate change, carbon sequestration in soil was never mentioned in the 1997 Kyoto Protocol, which set down broad greenhouse gas emission reduction targets for the world’s nations.
California began an initiative in 2015 to incorporate soil health into the state’s farm and ranch operations. Some of the pioneering studies showing regenerative agriculture’s benefits have been carried out at the Marin Carbon Project, on a self-proclaimed carbon-farming ranch in the pastoral reaches of Marin County 30 miles northwest of San Francisco. A four-year study there showed that a one-time application of compost caused an increase in plant productivity that has continued ever since, and that the soil’s carbon content grew year after year, at a rate equivalent to the removal from the atmosphere of 1.5 metric tons of carbon dioxide per acre annually.
Whendee Silver, an ecosystem ecologist at the University of California at Berkeley who is the project’s lead scientist, calculated along with a colleague that if as little as 5 percent of California’s grangelands was coated with one-quarter to one-half inch of compost, the resulting carbon sequestration would be the equivalent of the annual greenhouse emissions of nine million cars. The diversion of green waste from the state’s overcrowded landfills would also prevent it from generating methane, another potent greenhouse gas.
Some scientists remain skeptical of regenerative agriculture, arguing that its impact will be small or will work only with certain soils. It also faces significant obstacles, such as a scarcity of research funding and the requirements of federal crop insurance, which frequently disqualifies farmers who plant cover crops. But fears that the Trump administration would squelch government support for it so far have proved unfounded.
Consider the experience of Willie Durham, a soil health specialist at the federal Department of Agriculture’s Natural Resources Conservation Service in Temple, Tex. What led Mr. Durham to regenerative agriculture was his discovery while a Texas state agronomist of the “pesticide treadmill”: “People I’d known for a long, long time would ask me, ‘If nothing is changed in our agricultural system, why are we using two to three times as much fertilizer to accomplish the same thing?’ It got to where we spent so much on inputs that we didn’t make any profit.”
Now Mr. Durham teaches regenerative agriculture to farmers in Texas and Oklahoma. The farmers he inspires are predominantly young, not yet habituated to conventional agriculture — he estimates that about 10 percent of his students use the information, and the percentage is increasing. In a region where rainfall is usually precious, some conventional soil has become so lifeless that it absorbs as little as half an inch of water per hour, Mr. Durham said, while regenerative fields can absorb more than eight inches an hour.
Mr. Durham’s farmers are learning a lesson that resonates throughout human interactions with the natural world: People reap more benefit from nature when they give up trying to vanquish it and instead see it clearly, as a demanding but indispensable ally. Because of carbon’s climate change connection, we’ve been conditioned to think of it as the enemy, when in fact it’s as vital to life as water. The way to make amends is to put it back in the soil, where it belongs.
Jacques Leslie (@jacqules) is a Los Angeles Times contributing opinion writer and the author of “Deep Water: The Epic Struggle Over Dams, Displaced People, and the Environment.”