07 December, 2015

Introduction to Sequestering Carbon In The Soil For Gardeners

Prosopis velutina - a mesquite from Sonoran Arizona
probably is one of the plants of our future
We already know that the level of carbon in the atmosphere is beyond acceptable levels. No agreement in France or anywhere else is going to reduce the level of carbon to levels that are necessary for the human species to survive without some pretty radical changes in our relationships with the planet and our human activities.

On the global level, governments are merely trying to cope with mitigating the damage we've caused and the resultant damage humans will suffer in turn. We already know about acidification of our oceans and the indication that the ocean's temperature increase of only .3ºF has started release of plumes of methane – another greenhouse gas – from the ocean floor. If this loop becomes established it could mean that NOTHING humankind can do to prevent collapse of our world's ecosystem. I'm not trying to paint a more bleak picture than there is already. It is pretty scary.

As usual, with these global environmental problems, individuals feel powerless to make substantial changes that can influence the outcomes. In this case, farmers can play a significant role and gardeners can also contribute. The way I advocate we garden already sequesters carbon in the soil and now we know how to even more effectively sequester carbon by combining parts of the garden that were formerly segregated and to interplant annuals with perennials. Simply using appropriate actions in our farming and gardening, we can emphasize carbon sequestration in the soil. It is a win/win propostion.

An important vehicle for moving carbon into soil is root, or mycorrhizal, fungi, which govern the give-and-take between plants and soil. According to Australian soil scientist Christine Jones, plants with mycorrhizal connections can transfer up to 15 percent more carbon to soil than their non-mycorrhizal counterparts. The most common mycorrhizal fungi are marked by threadlike filaments called hyphae that extend the reach of a plant, increasing access to nutrients and water. These hyphae are coated with a sticky substance called glomalin, discovered only in 1996, which is instrumental in soil structure and carbon storage. The U.S. Department of Agriculture advises land managers to protect glomalin by minimizing tillage and chemical inputs and using cover crops to keep living roots in the soil.  Yale University Research Report, Soil as Carbon Storehouse: New Weapon in Climate Fight?

Research suggests that it is more beneficial to have plants with an active mycorrhizal community. This aligns with the very propositions I have been proposing for over 15 years. The Yale report mentions that pesticides and fertilizers interrupt the biological cycle and the presence of the mycorrhizae, which is prerequisite for sequestering carbon in the soil.

The following gardening practices are included:
  • Conservation tillage – minimize or eliminate manipulation of the soil for food production. Including leaving crop residues on the soil surface. Reduces soil erosion and improves water use efficiency and increases carbon concentrations in the top soil. Avoids disruption to the mycorrhiza in the soil and provides channels for water to penetrate more deeply in the soils.
  • Cover cropping – use of crops such as clover, alfalfa and small grains for soil protection and improvement between seasons of growing food. Cover crops enhance the soil structure and add organic matter to the soil making it better for carbon sequestration.
  • Crop rotation – by rotating crops in succession in the same area, we mimic the diversity of natural ecosystems more closely. How effective this is, however is related to the crops involved and the amount of time devoted to each one. (Millet is shallow rooted and is less efficacious than the same amount of time devoted to alfalfa which has a massive root structure.)
  • Zero use of chemical fertilizer and pesticides – already noted as detrimental to mycorrhiza/soil relationships – all of these are petroleum products that kill off the mycorrhiza in the soil and ruin exactly what you are trying to build. Besides, we will need to wean ourselves off petroleum anyway, might as well start now learning how to do without the stuff. Once you accept NOT using these items, it doesn't take long for one to learn how to live without them and soon you see how superfluous they were all along.
  • Mulching – placing organic matter over the soil and allowing it to breakdown without disturbing the process sequesters carbon. This is what creates the bases of all you want to achieve. Don't scrimp.
  • Growing perennial crops – often with interspersed annual crops where practical, leaving the detritus on the soil between growing seasons. Perennial crops lend themselves to soil sequestration better than annual crops and survive untoward weather fluctuations on a seasonal basis without dying. Their mere presence makes cultivation more difficult and ensures a limited disturbance of the soil.

Keeping in mind those practices, let's concentrate on perennial crops as they afford the easiest effort to go with no-till and will increase the carbon in the soil with very little effort on our part.
Perennial crops include a wide variety of different crops and more are coming online all the time.

Trees – nut and fruit trees are the first that come to mind. Plant a tree and, all things being equal, you have food production for many years to come – even decades. In our area, apple, almond, apricot, avocado, citrus, figs, peaches, pears (only a few varieties work here), persimmon, pomegranates, nectarines, and others are easy, requiring only a little pruning attention annually and certainly no plowing. Clover and other ground cover crops grown in between your trees and other perennials will enhance your soil and increase the sequestration of carbon.

There are many shrubs and similar plant forms that are wonderful for sequestration.

Beans – some of the climbing beans are really perennials – like Christmas Lima, Scarlet and other runner beans
Bramble berries
Blue Berries
Cactus – certain varieties
Jerusalem artichoke
Kiwi fruits
Onions (bunching or walking onions)
Wheat – perennial types

There are several perennial varieties of wheat and I have heard of perennial varieties of other grains as well. These are going to be quite important in the our very near future. I would encourage everyone to keep an eye out for them and eagerly try growing and using them. I do not believe this list is exhaustive. Keep your eyes open for other opportunities to plant food once and harvest over and over again.

What I am expressing is very much like the concept of the 'food forest' found in permaculture and in many other approaches to gardening. Other terms that might be encountered include Agroforestry or Woody Perennial Polycultures. These are essentially the same practice varying only in the fine print.
Furthermore, with these no-till techniques, we are just starting to transition to more permanent groupings of ever-bearing, perennial food plant groupings that include natural windrows, water harvesting/filtration and wildlife habitats – in addition to feeding the world.

The most important point is to leave the ground as little disturbed as possible. Try to avoid that in all your gardening activities of planting, weeding and harvesting. Whatever causes the soil the least manipulation, this is the goal to strive for.

This style of gardening also encourages beneficial insects, pollinators and is, of course, wholly organic. The food grown will have an overall better nutrition and will be less work. It will, of course, probably be less “neat” in the modern way of thinking, but that is merely a human construct. There are different levels of 'neatness' that are more important!


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