Rescue Earth System

Soil Carbon Storage

Soils have a high carbon sink capacity and soil carbon sequestration & storage has many co-benefits such as food security, increasing supply and quality of water, enhancing biodiversity, etc.

Soil Carbon Sequestration

Organic matter is a key component of soil fertility

The world’s soils hold a significant amount of carbon – more than double the amount in the atmosphere. The Intergovernmental Panel on Climate Change’s most recent report finds that storing, or “sequestering,” carbon will be essential in lowering atmospheric carbon levels. Agriculture, forestry and other land use practices that store carbon in the ground offer an opportunity to mitigate climate change. Healthy soils with more organic matter can store carbon while providing agricultural and environmental benefits.

Soil Carbon sequestration & storage can strengthen land-based Carbon sinks and off-set anthropogenic emissions. Degraded and depleted soils of agro-ecosytems have a high Carbon sink capacity. Soil Carbon sequestration is a cost-effective and a win–win option. Among numerous co-benefits of soil Carbon sequestration are advancing food security, increasing supply and quality of water, enhancing biodiversity, among others.

Soil Carbon and the Global Carbon Cycle

The amount of carbon (C) in soil represents a substantial portion of the carbon found in terrestrial ecosystems of the planet. Total C in terrestrial ecosystems is approximately 3170 gigatons (GT; 1 GT = 1 petagram = 1 billion metric tons). Of this amount, nearly 80% (2500 GT) is found in soil (Lal 2008). Soil carbon can be either organic (1550 GT) or inorganic carbon (950 GT). The latter consists of elemental carbon and carbonate materials such as calcite, dolomite, and gypsum (Lal 2004). The amount of carbon found in living plants and animals is comparatively small relative to that found in soil (560 GT). The soil carbon pool is approximately 3.1 times larger than the atmospheric pool of 800 GT (Oelkers & Cole 2008). Only the ocean has a larger carbon pool, at about 38,400 GT of C, mostly in inorganic forms (Houghton 2007).

Soil Carbon Sequestration

A New Paradigm for Climate Change

By: Todd A. Ontl (Department of Natural Resource Ecology and Management, Iowa State University, Ames, IA) & Lisa A. Schulte (Department of Natural Resource Ecology and Management, Iowa State University, Ames, IA) © 2012 Nature Education

Soil carbon sequestration is a process in which CO2 is removed from the atmosphere and stored in the soil carbon pool. This process is primarily mediated by plants through photosynthesis, with carbon stored in the form of SOC. In arid and semi-arid climates, soil carbon sequestration can also occur from the conversion of CO2 from air found in soil into inorganic forms such as secondary carbonates; however, the rate of inorganic carbon formation is comparatively low (Lal 2008).

Since the industrial revolution, the conversion of natural ecosystems to agricultural use has resulted in the depletion of SOC levels, releasing 50 to 100 GT of carbon from soil into the atmosphere (Lal 2009). This is the combined result of reductions in the amount of plant roots and residues returned to the soil, increased decomposition from soil tillage, and increased soil erosion (Lemus & Lal 2005).

Depletion of SOC stocks has created a soil carbon deficit that represents an opportunity to store carbon in soil through a variety of land management approaches. However, various factors impact potential soil carbon change in the future, including climatic controls, historic land use patterns, current land management strategies, and topographic heterogeneity.

Riverine ecological restoration can have a big impact on surrounding habitats and carbon sequestration

Continued increases in atmospheric CO2 and global temperatures may have a variety of different consequences for soil carbon inputs via controls on photosynthetic rates and carbon losses through respiration and decomposition. Experimental work has shown that plants growing in elevated CO2 concentrations fix more carbon through photosynthesis, producing greater biomass (Drake et al. 1997).

However, carbon loss may also increase due to increased plant respiration from greater root biomass (Hungate et al. 1997), or from accelerated decomposition of SOM through increased microbial activity (Zak et al. 2000). Likewise, increased temperatures may impact the carbon balance by limiting the availability of water, and thus reducing rates of photosynthesis.

Alternatively, when water is not limiting, increased temperatures might increase plant productivity, which will also impact the carbon balance (Maracchi et al. 2005). Increased temperatures may also lead to higher rates of SOM decomposition, which may in turn produce more CO2, resulting in positive feedbacks on climate change (Pataki et al. 2003).

At the scale of a watershed or crop field, the carbon sequestration capacity of the soil may be influenced by local controls on ecosystem processes. Processes such as rainfall infiltration, soil erosion and deposition of sediment, and soil temperature can vary on local scales due to landscape heterogeneity — all of which affect carbon input and carbon loss rates (Fig. 6), resulting in differences in SOC contents along topographic gradients (Thompson and Kolka 2005).

For example, slope position impacts soil moisture and nutrient levels, with subsequent impacts on the root growth of plants that may have consequences for soil carbon (Ehrenfeld et al. 1992). The combined effects of changes in carbon inputs and losses from land use, land management, and landscape-level effects on carbon input and loss rates result in variation in the carbon sequestration capacity across landscapes.

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