Carbon sequestration is the long-term removal, capture, or sequestration of carbon dioxide from the atmosphere to slow or reverse atmospheric carbon dioxide pollution and curb climate change.
Agricultural practices has huge carbon sequestration potentials.
Biosequestration
Biosequestration is the capture and storage of the atmospheric greenhouse gas carbon dioxide (CO2) by continual or enhanced biological processes. This form of carbon sequestration occurs through increased rates of photosynthesis via land-use practices such as reforestation, and sustainable forest management.
Peatland
Peatlands act as a sink for carbon because they accumulate partially decayed biomass that would otherwise continue to decay completely. There is a variance on how much the peatlands act as a carbon sink or carbon source that can be linked to varying climates in different areas of the world and different times of the year. By creating new ones, or enhancing existing ones, the amount of carbon that is sequestered by them can be increased.
Forestry
One of the most effective methods of carbon sequestration is Afforestation. The best way is planting more trees in an area with no previous tree cover and Reforestation or replanting trees on marginal crop and pasture lands to incorporate carbon from atmospheric CO2 into biomass. For this carbon sequestration process to succeed, the carbon must not return to the atmosphere from mass burning or rotting when the trees die. It is a best practice to take routine care and properly manage forested areas.
Alternatively, sequestered the wood from the tress via biochar, bio-energy with carbon storage, landfill, or ‘stored’ using them in construction. Short of growth in perpetuity, however, reforestation with long-lived trees (100+ years) will sequester carbon for a substantial period and be released gradually, minimizing carbon’s climate impact. The surface of Earth offers enough room to plant an additional 1.2 trillion trees. Planting and protecting them would offset some ten years of CO2 emissions and sequester 205 billion tons of carbon. Restoring all degraded forests world would capture about 205 billion tons of carbon in total, which is about two-thirds of all carbon emissions.
Wetlands
Wetland restoration involves restoring a wetland’s natural biological, geological, and chemical functions through re-establishment or rehabilitation. It is a potential climate change mitigation strategy. This method of carbon sequestration is known as blue carbon.
Wetland soil, particularly in coastal wetlands such as mangroves, seagrasses, and salt marshes, is an important carbon reservoir; 20-30% of the world’s soil carbon is found in wetlands, while only 5-8% of the world’s land is composed of wetlands. Restored wetlands can become productive CO2 sinks. Many restoration projects have been enacted around the world. Aside from climate benefits, wetland restoration and conservation can help preserve biodiversity, improve water quality, and aid with flood control.
As with forests, for the sequestration process to succeed, the wetland must remain undisturbed. If it is disturbed somehow, the carbon stored in the plants and sediments will be released back into the atmosphere, and the ecosystem will no longer function as a carbon sink. Additionally, some wetlands can release non-CO2 greenhouse gases, such as methane, which could offset potential climate benefits.
Farming
When soil converts from its natural land or semi-natural land, such as forests, woodlands, grasslands, steppes, and savannas, the soil organic carbon (SOC) content in the soil reduces by about 30–40%. The loss is due to the removal of plant material containing carbon while harvesting the crop. When the land-use changes, the carbon in the soil will either increase or decrease, this change will continue until the ground reaches a new equilibrium. Deviations from this equilibrium can also be affected by variations in the climate.
Steps to counter the decrease in SOC content can be done with several strategies – leave harvest residues on the field, use manure as fertiliser or include perennial crops in the rotation. Perennial crops have larger below ground biomass fraction, which increases the SOC content. Globally, soils are estimated to contain more than 8,580 gigatons of organic carbon, about ten times the amount in the atmosphere and much more than in vegetation.
Modification of agricultural practices is a recognized method of carbon sequestration as the soil can act as an effective carbon sink, offsetting as much as 20% of 2010 carbon dioxide emissions annually. Restoration of organic farming and earthworms may cancel CO2 annual carbon excess of 4 Gt per year and draw down the residual atmospheric excess.
Carbon emission reduction methods in agriculture have two categories: reducing and/or displacing emissions and enhancing carbon removal. Some of these reductions involve increasing the efficiency of farm operations while some include interruptions in the natural carbon cycle. Other effective techniques (such as the elimination of stubble burning) can negatively impact other environmental concerns (increased herbicide use to control weeds not destroyed by burning).
Carbon Farming
Carbon farming is an agricultural method aimed at sequestering atmospheric carbon into the soil and crop roots, wood, and leaves. Increasing soil’s carbon content can aid plant growth, increase soil organic matter (improving agricultural yield), improve soil water retention capacity, and reduce fertilizer use. As of 2016, variants of carbon farming reached hundreds of millions of hectares globally, of the nearly 5 billion hectares of world farmland. Soils can contain up to 5% carbon by weight, including decomposing plant and animal matter and biochar.
Potential sequestration alternatives to carbon farming include:
- Scrubbing CO2 from the air with machines (direct air capture).
- Fertilizing the oceans to prompt algal blooms that, after death, carry carbon to the sea bottom.
- Storing the carbon dioxide emitted by electricity generation.
- Crushing and spreading types of rock such as basalt that absorb atmospheric carbon.
Land management techniques combined with farming include planting/restoring forests, burying biochar produced by anaerobically converted biomass, and restoring wetlands.
Bamboo Farming
Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequester carbon faster than a mature forest or a tree plantation. Therefore, bamboo timber farming may have significant carbon sequestration potential.
Deep Soil
Increasing yields and efficiency generally reduce emissions since more food results from the same or less effort. Techniques include:
- More proper fertilizers.
- Less soil disturbance.
- Better irrigation.
- Crop strains bred for locally beneficial traits and increased yields.
In practice, most farming operations that incorporate post-harvest crop residues, wastes, and byproducts back into the soil provide a carbon storage benefit. This is particularly the case for practices such as field burning of stubble – rather than releasing almost all of the stored CO2 to the atmosphere, and tillage incorporates the biomass back into the soil.
All crops absorb CO2 during growth and release it after harvest. Agricultural carbon removal aims to use the crop and its relation to the carbon cycle to sequester carbon within the soil permanently. This is done by selecting farming methods that return biomass to the soil and enhance the conditions in which the carbon within the plants will be reduced to its elemental nature and stored in a stable state. Methods for accomplishing this include:
- Use cover crops such as grasses and weeds as a temporary cover between planting seasons.
- Concentrate livestock in small paddocks for days at a time, so they graze lightly but evenly.
- Cover bare paddocks with hay or dead vegetation.
- Restore degraded land, which slows carbon release while returning the land to agriculture or other use.
Agricultural sequestration practices may positively affect soil, air, and water quality, benefit wildlife and expand food production.
Many factors affect the costs of carbon sequestration, including soil quality, transaction costs, and various externalities such as leakage and unforeseen environmental damage. Because reduction of atmospheric CO2 is a long-term concern; farmers can be reluctant to adopt more expensive agricultural techniques when there is no clear crop, soil, or economic benefit.