Carbon Farming: Building Soils and Stabilizing the Climate

Excerpted from the forthcoming Carbon Farming: Stabilizing the Climate with Perennial Crops and Regenerative Agricultural Practices

Figure 1*: Carbon farming practices on display at the Las Cañadas farmer cooperative and agroecology center in Veracruz, Mexico. This aerial photo shows improved annual cropping (organic, crop rotation, cover crops), annual-perennial integration (alley cropping, contour hedgerows), livestock practices (livestock integration, managed grazing, fodder banks, living fences), and perennial cropping systems (tree crops, multistrata agroforestry, coppiced firewood plots).

Climate change will have a huge impact on the world’s poorest people. Crop yields have already gone down in the tropics and are projected to drop by 15-30% by 2080 in Africa, South Asia, and Central America (Hoffman 2013). Some countries could reach a 50% loss of agricultural productivity; in fact, in some regions, agriculture will likely become impossible (Hoffman 2013). The poorest and most food-insecure countries face the worst impacts of climate change to their farming systems (Oxfam 2009). Oxfam International’s Suffering the Science reports that 26 million people are already displaced from their homes due to climate change, and the World Health Organization estimates 150,000 lives are being lost every year due to climate change (Oxfam 2009).

Climate change is happening because too much carbon dioxide is being released into the atmosphere, due to burning of fossil fuels, deforestation, and degradation of farmland. To make our climate stable again, we must drastically reduce emissions of carbon dioxide and other greenhouse gases, while also drawing down the excess carbon in the atmosphere and safely storing it. Many agricultural practices can do this. In fact, if these techniques were widely used, they could remove and store enough carbon to return the atmosphere to 350 parts per million (ppm) of carbon dioxide, which is the amount scientists think is safe (Lal 2014). However, such techniques will only be successful if emissions are also dramatically reduced.

Carbon sequestration is the act of moving excess carbon dioxide from the atmosphere into long-lived storage. In agriculture, this means storing it in the soil and in perennial plants like trees (Nair et al. 2010). Carbon farming is a term that describes these carbon-sequestering practices (Fig. 1).

Here’s how it works. During photosynthesis, plants take carbon dioxide out of the atmosphere and turn it into carbohydrates inside their cells. Some of this carbon stays in the biomass of the plant, like the trunks, roots, and branches of trees. About 50% of the dry weight of plants is carbon (Nair 2011). Carbon can be stored for decades or even centuries in perennial plants like fruit and nut trees. 

Carbon from photosynthesis also makes its way into the soil. Remarkably, within one hour of photosynthesis, 10-40% of these carbohydrates are exuded through the roots into the soil to feed soil organisms (Kumar et al 2006). More carbon becomes part of the soil over time through decomposition of leaves, roots, and other plant parts (Kumar et al 2006). As this material decomposes, some of the carbon becomes carbon dioxide and returns to the atmosphere, but much becomes organic matter. Soil organic matter is 58% carbon (dry weight), and represents another long-term sequestration opportunity (USDA NRCS). If the soil is not tilled, carbon can be held in organic matter for at least a century (USDA NRCS). 

Soil organic matter does more than sequester carbon. It can improve crop yields, moderate acidic or alkaline soils, prevent plant diseases, and improve soil water holding capacity (Lal 2014). Indeed, Courtney White writes in Grass, Soil and Hope: A Journey Through Carbon Country, “You can’t increase soil carbon with a practice that degrades the land” (White 2013). What is good for the climate is good for the farmer too.

Somewhere between one third and three quarters of the world’s farmland is degraded, meaning much of the soil carbon is gone and yields are reduced (FAO). Most agricultural soils have lost 30-40 metric tons** of carbon per hectare, which is 25-75% of what was there before the land was cleared and farmed (Lal 2014). The rate and amount of carbon loss varies widely with original ecosystem, soil type, and farming practice. For example, soil loses 30-50% of its organic carbon after 50 years of cultivation in temperate climates, but such loss takes only 10 years of cultivation in tropical regions (Lal 2014). The rate of loss is much worse in easily eroded or degraded soils (Lal 2014). Carbon farming techniques can help restore these lands to productivity while fighting climate change. As we shall see, the reality of climate change may also lead to funding opportunities to bring these lands back to health.

Carbon farming techniques fall into five broad groups: improved annual cropping systems; integrating annuals with perennials; livestock systems; fully perennial systems; and other techniques. Most of these have been promoted by ECHO for decades, and each has its pros and cons. For example, systems that produce foods we know and love (like cereal grains and meat) sequester less carbon, and some result in methane emissions. Perennial systems sequester large amounts of carbon, but may require a substantial change in diet. Each broad group of carbon farming techniques is described below. 

Improved Annual Cropping Systems

Figure 2: Cambodian farmer Sin Chhukrath harvesting SRI rice. Image: Oxfam International.

Improved annual cropping systems include the following practices: crop rotations, green manures, and cover crops; mulching, reduced bare fallows, and reduced tillage; the System of Rice Intensification (Fig. 2) and improved rice paddy management; nutrient management; and organic production. These can sequester low but significant amounts of carbon, typically 2 tons per hectare per year or less (Seeberg-Elverfeldt and Tapio-Bistrom 2012). Organic systems range from 0.7-2.3 t/ha/yr (Seebert-Elverfeldt and Tapio-Bistrom 2012; Hepperly et al. 2009). Conservation agriculture is estimated to sequester 0.1-1 t/ha/yr (Lal 2014). Improved annual cropping systems have many advantages: they allow us to keep the crops we know and love; they don’t require big changes in production, harvesting, or processing machinery; and they can be implemented at a wide scale on the world’s vast annual croplands. 

Integrated Annuals and Perennials

Figure 3: Evergreen agriculture: Faidherbia with annual crops beneath, Zambia. Image: World Agroforestry Center. 

Perennial-annual integration systems combine annual cropping systems with a perennial element or elements, as in many agroforestry and vetiver systems. The perennials may be intercropped with annuals, but they can also be randomly scattered, leaf out in different seasons, or be planted in rows or strips. This carbon farming category includes windbreaks and living fences; strip intercropping and alley cropping; Sloping Agricultural Land Technology and contour hedgerows; riparian buffers; FMNR; evergreen agriculture with Faidherbia albida (Fig. 3); long swidden rotations; and improved fallows.

Carbon sequestration by perennial-annual integrated systems is generally low, but higher than that of improved annuals alone. Annual sequestration rates have been found as follows: 2-4 t/ha/yr for Farmer Managed Natural Regeneration (FMNR) (Garrity et al. 2010), 2-4 t/ha/yr for Faidherbia evergreen agriculture (Garrity et al. 2010), 0.3-4.6 t/ha/yr for poplar intercropping (Seebert-Elverfeldt and Tapio-Bistrom 2012), and 2.5-3.4 t/ha/yr for alley cropping (Udawatta and Jose 2011). Systems that integrate annuals and perennials allow consumption of the annual crops with which people are familiar, with supplementation from tree crops.

Livestock Systems

Figure 4: Silvopasture area with cattle under trees in restored traditional Ngitili system, Tanzania. Image: World Agroforestry Center.

Carbon-friendly livestock systems generally pair perennial pastures with livestock, and have their best climate impact when woody plants are incorporated. Carbon sequestration of managed grazing systems varies and is countered by the impact of methane emissions from ruminant livestock like cattle (O’Brien et al. 2014). In some grazing examples, the impact of methane emissions can almost completely negate carbon gains – though this is not the case in silvopastures (trees in pastures; Fig. 4). Managed grazing and improved pasture management sequester a global average of 2.1 tons of carbon per hectare per year (Tennigkeit and Wilkes 2008). Silvopastures sequester 1-6 t/ha/yr (Udawatta and Jose 2011). A remarkable new practice called intensive silvopasture includes a very high density of trees and can sequester 8-26 tons of carbon per hectare per year in the humid tropics, even when accounting for methane impacts (while also producing 2-10 times more meat per hectare) (Cuartas et al. 2014). Other carbon-friendly livestock practices include integrating livestock with crops; establishment of fodder banks; and use of perennial feeds. Livestock are less picky than people, and are usually happy to eat perennial feeds and fodders. This makes high-carbon perennial systems possible without changing the human diet very much; the livestock taste the same whether they eat annual or perennial foods.

Fully Perennial Systems

Figure 5: Multistrata systems involve different layers of vegetation. In this case, avocadoes and macadamias are grown above bananas, which in turn provide shade for coffee. Veracruz, Mexico.

Fully perennial systems tend to have the highest carbon impact. They can require a serious change in diet, particularly the use of perennial staple crops. Both the crops and production systems are well-developed in the humid tropics but need development for drier and colder regions. Perennial crops in monocultures can sequester from 1-20 tons per hectare annually according to my review of multiple studies on individual crops (Lamade and Bouillet 2005; Geesing, Felker and Bingham 2000; Schroth et al. 2002; Brakas and Aune 2011). Woody species tend to sequester more than herbaceous perennials. Multistrata agroforestry systems like shade cacao, shade coffee (Fig. 5), tropical homegardens, and other multi-layered ‘food forests’ have been found to sequester 3-40 t/ha/yr (Schroth et al. 2002; Seebert-Elverfeldt and Tapio-Bistrom 2012). Perennial versions of staple grains like rice are under development. These are predicted to sequester a much more modest 0.5 t/ha/yr, but don’t require a difficult change in staple foods (Rumsey 2014). 

Additional tools exist to sequester more carbon in the landscape. These include: rainwater harvesting, terracing, biochar, and restoration of productive traditional indigenous land management practices.

Funding Opportunities

ECHO network members know that farmers face many barriers when implementing new crops and practices. Typically it takes several years to recover the costs of transition. (McCarthy et al. 2011). There are efforts underway to provide funds to farmers, farmer associations, and groups that serve farmers to support increased adoption of carbon farming practices (Fig. 6).

Carbon offsets allow companies and individuals to counterbalance their carbon emissions by financing mitigation efforts like tree planting. Only a small percentage of this money goes to agriculture and forestry, though in 2013 carbon offsets funds for these practices was over $6 billion (Buchner et al. 2011). Unfortunately these funds are currently difficult for smallholders and smallholder associations to access (De Pinto et al. 2012). Many practices are currently ineligible for funding (Havemann 2011). 

Figure 6: Women farmers in a village in Senegal discuss a contract with the AROLMOM carbon project under a large mango tree. Image: World Agroforestry Center.

Private foundations, online ‘crowd-sourced’ fundraising, green investing groups, and large foundations and universities that are divesting from fossil fuels are all candidates for financing widespread adoption of carbon farming. This alternative financing sector has become very significant to farmers in countries like the US, and could potentially be extended globally (Ü 2013).

Market- and consumer-driven strategies are also underway. For example, the Sustainable Agriculture Network (SAN) is an international body that certifies organic and other practices on farms. SAN has developed a Climate Module to certify climate-friendly agriculture. Over 200,000 farmers on 1 million hectares in Latin America and Africa have received the certification (Rainforest Alliance). Though there is not yet a market for carbon-certified products, and the Climate Module looks more at reduced emissions than carbon sequestration, this is a hopeful step. Premium prices for carbon-farmed products, analogous to organic certification, could help make wide conversion possible. 

National policies can also have a positive impact, through models like Payment for Environmental Services (Lal 2014). India’s visionary new national agroforestry policy, that mandates an increase in national forest cover from 25% to 33% through increased agroforestry, is a powerful example (Kapsoot 2014).

Though large-scale financial support for carbon farming is not yet here, it is very likely to be at the heart of future mitigation efforts. The International Panel on Climate Change recommends carbon farming practices as an important component of climate change mitigation (IPCC 2014). Project Drawdown is a new effort, led by famous environmentalist Paul Hawken, to promote one hundred climate solutions. Fully one third of their strategies are biosequestration strategies (carbon farming and forestry) (Project Drawdown).

There is recognition that climate mitigation efforts that have additional social and environmental benefits can amplify the impact of such funds, while drawing in greater support (Lal 2014). Carbon farming is also noted to be a very cost-effective mitigation strategy (IPCC 2014). International support for carbon farming may represent a new reason for the world to recognize the hard work of ECHO network members and the farmers they work with. Development workers can begin by keeping records on the carbon farming practices already being implemented in the communities they serve. They can also be keeping their eyes out for carbon farming funding sources, as they emerge.

*All images in this article are open source from Creative Commons.

**Note that all tons referred to in this article are metric tons.

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