# Soil: Important Sink for Carbon Sequestration

Ajeet Kumar, C.K Jha

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Ajeet Kumar, C.K Jha. Soil: Important Sink for Carbon Sequestration. 2021, pp.3 (5): 49-51. hal-05456915

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Submitted on 13 Jan 2026

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# Soil: Important Sink for Carbon Sequestration

Article ID: 10817

Ajeet Kumar<fnref n="1" />, C. K. Jha<fnref n="1" />

## Abstract

Carbon management is a serious concern confronting the world today. The current level of carbon in the atmosphere is about 375 ppm. It is estimated that if the carbon increases in the atmosphere at the present rate, then the level of carbon in the atmosphere would go up to 800–1000 ppm by the end of century. Soil may be an important sink for the carbon storage in the form of soil organic carbon. This form of carbon is also a matter of serious concern for agricultural scientists across the globe because various researches reveal that the soil under intensive cultivation results in declining potential productivity due to reduction in soil organic carbon, thereby proving an obstacle for sustainable agriculture. Plants are the main source of the soil organic carbon. About 40% of the photosynthates synthesized in the plant parts are lost through the root system into the rhizosphere within an hour. The plant rhizosphere is different compared to bulk soil with respect to physical, chemical and biological properties. Thus, the aim of this article is to provide an insight on transfer of carbon from atmosphere to rhizosphere and further their significance in sustainable agriculture.

## Introduction

Carbon sequestration is the process of removing carbon deliberately from the atmosphere and depositing it in a reservoir. Thus, it is the process of carbon capture and storage. Carbon sequestration describes long-term storage of carbon dioxide or other forms of carbon to either mitigate or defer global warming. Carbon dioxide is naturally captured from the atmosphere through biological, chemical or physical processes. Biological processes include, Peat production, Forestry, Agriculture, and Ocean-related while Physical processes includes, Biomass-related, and subterranean injection, Chemical processes like Industrial use, Chemical scrubbers, and Ocean-related. Peat bogs are important carbon store. By creating new bogs, or enhancing existing ones, carbon can be sequestered. Replanting of trees on marginal and pasture lands to incorporate carbon from atmospheric CO2 into biomass.

## Soil an Important Sink for the Carbon Storage

Globally, soils are estimated to contain approximately 1,500 gigatons of organic carbon, more than the amount in vegetation and the atmosphere. Modification of agricultural practices is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of carbon dioxide emissions annually. Carbon emission reduction methods in agriculture are grouped into two categories:

1. Reducing emissions i.e. using more fuel-efficient equipment, increased herbicide use to control weeds not destroyed by burning.

2. Enhancing carbon removal.

**Reducing Emissions:** Increasing yields generally reduces emissions, the techniques include more accurate use of fertilizers, less soil disturbance, and better irrigation and increased yields. Replacing more energy intensive farming operations also reduce emissions. No-till farming requires less machine use and burns correspondingly less fuel. However, no-till usually increases use of weed-control chemicals and the residue now left on the soil surface is more likely to release its CO2 to the atmosphere as it decays, reducing the net carbon reduction.

Most farming operations incorporate post-harvest crop residues, and by-products into the soil. This is particularly the case for practices such as field burning of stubble - rather than releasing almost all of the stored

<footnote n="1">¹Assistant Professor-cum- Scientist; Department of Soil Science, Sugarcane Research Institute, DRPCAU, Pusa (Samastipur)-848125, Bihar, India.</footnote>
CO₂ to the atmosphere, tillage incorporates the biomass back into the soil where it can be absorbed and a portion of it stored permanently.

## Crop Versus Carbon Cycle in Soil

All crops absorb CO₂ during growth and release it after harvest. The goal of agricultural carbon removal is to use the crop and its relation to the carbon cycle to permanently sequester carbon within the soil. This is done by 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:

1. Use cover crops and weeds as temporary cover between planting seasons. Allow animals to graze the grasses. This encourages roots to grow deeper into the soil.

2. Cover bare paddocks with vegetation. This protects soil from the sun and allows the soil to hold more water and be more attractive to carbon-capturing microbes.

3. Restore degraded land, which slows carbon release while returning the land to agriculture.

Agricultural sequestration practices may have positive effects on soil, air, and water quality, be beneficial to wildlife, and expand food production. On degraded lands, an increase of 1 ton of soil carbon pool may increase crop yield by 20 to 40 kg/ha of wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. The effects of soil sequestration can be reversed. If the soil is disrupted or tillage is abandoned, the soil becomes a net source of greenhouse gases. Typically, after 15 to 30 years of sequestration, soil becomes saturated and ceases to absorb carbon. This is a global limit to the amount of carbon that soil can hold.

## Ocean Fertilization and Carbon Cycle

The scientific evidence reveals that to fertilize the ocean with urea, to encourage phytoplankton growth into the ocean to boost CO₂ absorbing phytoplankton growth as a way to combat climate change. Iron fertilization also encourages phytoplankton growth, which removes carbon from the atmosphere. Encouraging various ocean layers to mix can move nutrients and dissolved gases. Mixing may be achieved by placing large vertical pipes in the oceans to pump nutrient rich water to the surface, triggering blooms of algae, which store carbon.

## Physical Processes

The biomass in power stations and boilers that use carbon capture and storage. The carbon sequestered by the biomass would be captured and stored, thus removing CO₂ from the atmosphere. Burying biomass directly mimics the natural processes that created fossil fuels. A landfill also represents a physical method of sequestration. Biochar is charcoal created by pyrolysis of biomass waste. The resulting material is added to a landfill or used as a soil improver. Biogenic carbon is recycled naturally in the carbon cycle. Further, the soil encourages bulking with organic matter, which gives additional sequestration benefit. In the soil, the carbon is unavailable for oxidation to CO₂ and consequential atmospheric release. River mouths bring large quantities of nutrients and dead material from upriver into the ocean that eventually produces fossil fuels.

## Subterranean Injection

Carbon dioxide can be injected into depleted oil and gas reservoirs or can be injected into the deep ocean. CO₂ has been used extensively in enhanced crude oil recovery operations. There are wells that inject CO₂. The gas comes in part from anthropogenic sources, but is principally from large naturally occurring geologic formations of CO₂. It is transported to the oil-producing fields through a large network of CO₂ pipelines.

## Chemical Processes

Carbon, in the form of CO₂ can be removed from the atmosphere by chemical processes, and stored in stable carbonate mineral forms. This process is known as 'carbon sequestration by mineral carbonation' or mineral sequestration. The process involves reacting carbon dioxide with abundantly available metal oxides-either
magnesium oxide (MgO) or calcium oxide (CaO) to form stable carbonates. These reactions are exothermic and occur naturally (e.g., the weathering of rock over geologic time periods).

$$CaO + CO_2 \rightarrow CaCO_3$$

$$MgO + CO_2 \rightarrow MgCO_3$$

Calcium and magnesium are found in minerals as calcium and magnesium silicates such as forsterite and serpentine. For forsterite and serpentine, the reactions are:

$$Mg_2SiO_4 + 2CO_2 = 2MgCO_3 + SiO_2$$

$$Mg_3Si_2O_5(OH)_4 + 3CO_2 = 3MgCO_3 + 2SiO_2 + 2H_2O$$

## Industrial Use

Traditional cement manufacture releases large amounts of carbon dioxide, but newly developed cement types can absorb CO₂ from ambient air during hardening. In oil shale ash, generated by power stations could be used as sorbents for CO₂ mineral sequestration. The amount of CO₂ captured averaged 60–65% of the carbonaceous CO₂ and 10–11% of the total CO₂ emissions.

## Chemical Scrubbers

Various CO₂ scrubbing processes have been proposed to remove CO₂ from the air, usually using a variant of the Kraft process. CO₂ scrubbing variants exist based on potassium carbonate, which can be used to create liquid fuels, or on sodium hydroxide. These notably include artificial trees to remove CO₂ from the atmosphere using chemical scrubbers.

## Ocean-Related Mechanism

Carbon dioxide sequestration in basalt involves the injecting of CO₂ into deep-sea. The CO₂ first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of Ca²⁺ and Mg²⁺ forming stable carbonate. Underwater basalt offers alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include geothermal, sediment, gravitational and hydrate formation. Because CO₂ hydrate is denser than CO₂ in seawater, the risk of leakage is minimal. Injecting the CO₂ at depths greater than 2,700 meters ensures that the CO₂ has a greater density than seawater, causing it to sink. Adding crushed limestone to oceans enhances the solubility, which naturally removes CO₂ from the atmosphere. Electrolysis also removes hydrochloric acid from the ocean for neutralization with silicate minerals. Electrolysis contributes to carbon addition to the ocean.

## Conclusion

The management of carbon is essential for the agriculture. The carbon level in the atmosphere is 375 ppm which is expected to increases to the level of 1000 ppm by the end of century, which may create havoc for all living creatures on earth. Soil would be an important sink for the carbon storage in the form of soil organic carbon. This form of carbon is also a matter of serious concern for soil scientists across the globe because the soil under intensive cultivation results in declining potential productivity due to reduction in soil organic carbon. Plants are the main source of the soil organic carbon. Thus, it is concluded that the transfer of carbon from atmosphere to rhizosphere has significance in sustainable agriculture production.

## References

1. Lal R. (2009). Soil Carbon Sequestration Impacts on Global Climate Change and Food Security. Science 304 (5677).

2. Fred Pearce (2007). Ocean pumps could counter global warming. New Scientist.

3. Christian Azar (2006). Carbon capture and storage from fossil fuels and biomass -costs and potential role in stabilizing the atmosphere. Climatic Change 74 (1-3): 47–79.

4. Lehmann J., Gaunt J., and Rondon, M. (2006). Bio-char sequestration in terrestrial ecosystems-a review. Mitigation and Adaptation Strategies for Global Change 11: 403-427.