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Carbon Farming Practices

What farming practices can help stabilize the climate by sequestering carbon? Almost anything that builds soil organic matter can do the trick, but some sequester much more carbon than others. Even low rates of carbon sequestration can make a huge difference if practiced on enough farms. Here’s a typology and comparison of these systems. Note that a hectare is roughly 2.5 acres. To learn more check out my upcoming workshop at the carbon farming course! Early registration ends December 15th.

Improved Annual Cropping Systems

These practices make our production of annual crops more carbon-friendly. These systems sequester low amounts of carbon, typically 1-2 tons per hectare per year. Their big advantage is they allow us to grow the crops we know and love, and we already have equipment and infrastructure for production, processing, and consumption. Some are already widely practiced, like no-till (111 million hectares), organic annual crops (6.3 million) and system of rice intensification (4-5 million farmers globally). Other practices include crop rotation, green manures, cover crops, use of compost, and mulching.

Organic no-till system developed by Rodale Institute. Image courtesy Rodale Institute..
Organic no-till system developed by Rodale Institute. Image courtesy Rodale Institute.

Perennial-Annual Systems

These systems integrate perennial elements like trees with the annual crops we already know and grow. They include many agroforestry practices. Carbon sequestration is low at 1-5 tons per hectare. The perennial elements may play support roles like slope stabilization or nitrogen fixation, or may be crops themselves. Some are widely practiced like shea nut parkland in Africa (23 million hectares), farmer-managed natural regeneration in Niger (4.8 million hectares), alley cropping with Paulownia trees in China (3 million hectares), and streuobst mixed fruit trees with annuals in Germany (1 million hectares). Other practices include contour hedgerows, windbreaks, living fences, pasture cropping, and evergreen agriculture.

intercrop at Denis Flores Agroforestry in France. Image Richard Perkins.
Strip intercropped timber poplars at Denis Flores Agroforestry in France. Image Richard Perkins.

Perennial-Livestock Systems

In these systems livestock are integrated with perennials like trees or pasture. Carbon sequestration is mostly low to medium with managed grazing around 2-4 tons per hectare per year, and silvopasture at 1-10. A few case studies have seen sequestration of 36 and even 40 tons per hectare. Generally the more trees, the more carbon. People already consume livestock products like meat, milk, and eggs, so we don’t need to change our diets – instead we let the animals eat the perennials. Ruminants do produce methane which can reduce the impact of carbon sequestration of these systems, though not reverse it. Again some of these are widely practiced, like holistic grazing (12-20 million hectares worldwide), dehesa silvopasture in Spain and Portugal (5.5 million hectares), and Central American silvopasture (9 million hectares). Practices include managed grazing, silvopasture (trees with pastrure), fodder trees and fodder banks, aquaforestry (aquaculture plus trees), and crop-livestock integration.

Alder silvopasture at Las Cañadas in Mexican highlands. Image Ricardo Romero.
Alder silvopasture at Las Cañadas in Mexican highlands. Image Ricardo Romero.

Fully Perennial Systems

These systems sequester the most carbon (medium to very high) but may require the biggest changes to our food system. Coppice and biomass systems can sequester 1-6 tons/hectare/year, with tree crops and bamboo much higher at 2-28 and 6-33 tons/hectare/year respectively. Multistrata agroforestry systems sequester a remarkable 4-40 tons/hectare/year making them the world’s best carbon-sequestering food production model (development of commercial multistrata models for cold climates largely awaits innovative producers and researchers).  Perennial crops are grown on 153 million hectares globally, along with bamboo (22 million hectares), cacao agroforestry systems (7 million hectares), and more. These systems include orchards and plantations, bamboo systems, traditional and short rotation coppice and biomass grasses, multistrata systems like tropical homegardens (food forests) and larger scale multi-layered perennial production systems, and newer systems like woody agriculture and perennial grain production. Perennial staple crops have have a major role to play in a carbon-friendly future but may require big changes in the way we farm and eat.

14.1d loaded chestnut
Chestnuts are already a global perennial staple crop with half a million hectares in production.
Commercial multistrata system featuring alder (for timber, firewood, and nitrogen fixation) over tea (shade crop).
Commercial multistrata system featuring alder (for timber, firewood, and nitrogen fixation) over tea (shade crop). Image World Agroforestry Center.
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Short-rotation coppice mechanized harvest of biomass willow. Image D. Angel, SUNY ESF.

Other Practices

These are mostly non-biological systems that involve design, equipment, or other non-living elements. Carbon sequestration is variable and in some cases (like keyline) unknown. Drip irrigation (which prevents soil salinization and carbon loss in dryland climates) is practiced on 10 million hectares globally, and Amazonian terra preta (biochar plus) includes perhaps a million hectares or more. This set of practices includes rainwater harvesting, keyline, productive restoration, and more.

Keyline farming at Rancho San Ricardo in Oaxaca, Mexico. Image Rodrigo Quiros.
Keyline farming at Rancho San Ricardo in Oaxaca, Mexico. Image Rodrigo Quiros.

These systems need to be combined with perennial crops, new technologies, new markets, citizen movements and policy changes to fully realize the potential of agriculture to sequester up 10-85% of the 200 gigatons needed to get us back down to the magic number of 350ppm.

 

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Legume Trees with Pods Edible by Livestock

This article is an excerpt from my forthcoming book Carbon Farming: A Global Toolkit for Stabilizing the Climate with Tree Crops and Regenerative Agriculture Practices, and is part of a series promoting my kickstarter campaign to raise funds with which to complete the book. You can pre-order a copy and help make it possible for me to get this book out soon.

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This painting by Joaquin Sorolla y Bastida shows sheep enjoying the shade and dropped pods of an ancient carob tree. Courtesy Wikimedia Commons.

Rotational grazing is one the most powerful tools we have to sequester carbon through agriculture. We can increase its carbon-sequestering capacity, and its livestock production power, by adding widely-spaced trees. This practice of integrating trees with grazing is called silvopasture. Studies have shown that in many cases trees actually increase the productivity of pasture beneath them, especially trees that cast light shade.

This article is about a particular kind of silvopasture, where the trees literally drop food to the livestock grazing below. Around the world there are many farming systems that utilize this concept, most famously the dehesa of Spain and Portugal which produces gourmet acorn-fed pork. Here I’m narrowing the focus a bit more, to legume trees that drop nutritious pods to the ground for ruminant livestock like cattle, sheep, and goats. There are “fodder pod trees” like this for most of the world’s climates.

Pods of carob, a tree for Mediterranean climates. Great livestock fodder and edible for humans as well.
Pods of carob (Ceratonia siliqua), an ancient Mediterranean crop. Great livestock fodder and edible for humans as well. Courtesy Wikimedia Commons.

These trees are providing more than just food for animals. Livestock enjoy the shade they provide, especially in the tropical sun. Many of these trees fix nitrogen. Some even have pods edible for humans.

Unfortunately not all of these pods fall to the ground when ripe, some must be knocked off the tree with poles, increasing labor requirements. To my knowledge there has been little or no breeding of these trees for the purpose of feeding livestock. The foliage of many serves as a fodder, and some make excellent firewood as well.

The great majority of these species hail from semi-arid Africa savannahs, but this may in part result from a lack of research in other regions. Surely there are many, many more. Savannahs would be the best place to search for such species as they have coevolved with large grazing and browsing animals. An asterisk (*) indicates pods also edible by humans. Sources: Nitrogen Fixing Tree Association NFT Highlights and World Agroforestry Center Agroforestree Database.

Latin Name Climate Native Range Nitrogen Fixation
Acacia leucophloea semi-arid tropical lowlands Asia yes
Acacia nilotica semi-arid tropical lowlands Africa yes
Acacia saligna semi-arid tropical lowlands Australia yes
Acacia senegal semi-arid tropical lowlands and highlands Africa yes
Acacia seyal arid to semi arid tropical lowlands Africa yes
Acacia tortolis arid to semi-arid tropical lowlands, highlands Africa yes
Adenanthera pavonina semiarid to humid tropical lowlands Asia yes
Cassia grandis humid lowland tropics tropical Americas some
*Ceratonia siliqua Mediterranean Mediterranean no
Enterolobium cyclocarpum     yes
*Erythrina edulis semi-arid to humid tropical highlands Andes yes
*Faidherbia albida arid to humid tropical lowlands and highlands Africa yes
*Gleditsia triacanthos cold humid and arid, Mediterranean, tropical highlands North America no
Newtonia buchananii humid tropical lowlands and highlands Africa no
*Parkia biglobosa semiarid to humid tropical lowlands Africa yes
*Parkinsonia aculeata arid to semiarid tropics and subtropics Americas no
*Piliostigma thongii semiarid tropics Africa yes
Pithecellobium dulce semi-arid to humid tropical lowlands Americas yes
Prosopis africana     yes
*Prosopis alba semi-arid tropics South America yes
Prosopis chilensis semi-arid tropics and subtropics South America yes
Prosopis cineraria arid to semi-arid tropical lowlands Asia & Middle east yes
*Prosopis glandulosa arid to semi-arid, subtropics to cold North America yes
*Prosopis juliflora     yes
*Prosopis pallida semiarid tropics South America yes
Prosopis tamarugo arid tropics South America yes
Samanea (= Albizia) saman semi-arid to humid tropical lowlands tropical Americas yes
Senna singueana semiarid tropics Africa no

Again note that nitrogen-fixing legumes are often likely to escape from cultivation. Always investigate your regional native plant resources first. I’m quite certain that there are tens or hundreds more species that produce fodder pods, as well as many more that drop food of one kind or another to ruminants. For example there are many more species of honey locust (Gleditsia) in Asia.

The pods of Acacia nilotica, from African semi-arid savannahs. Courtesy Wikimedia Commons.
The pods of Acacia nilotica, from African semi-arid savannahs. Courtesy Wikimedia Commons.
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Cassia grandis, from the humid tropical Americas. Courtesy Wikimedia Commons.
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The North American honey locust (Gleditia triacanthos), a good choice for cold temperate climates. Courtesy Wikimedia Commons.
The sweet pods of mesquite (Prosopis glandulosa), a nitrogen-fixing tree for cold, arid landscapes.
The sweet pods of honey mesquite (Prosopis glandulosa), a North America nitrogen-fixing tree for cold, arid landscapes. There are mesquites throughout the dry Americas as well as native species from Africa and Asia, for highlands and lowlands, arid and semi-arid climates. Courtesy Wikimedia Commons.