Soil Carbon

Soil organic matter is a natural climate solution

Humus, or soil organic matter, is largely carbon. Soil carbon (SOC) is a natural climate solution. Building soil carbon is an efficient way to reduce atmospheric carbon and to increase fertility of the soil.

Protecting and increasing SOC storage can:

1. Increase soil water holding capacity.

2. Protect or increase soil fertility.

3. Maintain and increase resilience to climate change.

5. Reduce soil erosion.

6. When implemented through the conversation of natural ecosystem, reduce habitat conversion which is in line with the United Nations Sustainable Development Goals (SDGs).

Soil organic carbon increases water holding capacity of the soil (Sarkar et all, 2017))

Organic matter helps soil to hold water and nutrients

The more carbon there is in the soil, the better the soil can hold nutrients and water Cation-exchange capacity (CEC) is a measure of how many cations can be retained on soil particle surfaces.

Soil Organic Carbon(SOC) is a component of Soil Organic Matter (SOM). Soil Organic Carbon counts for 58% of Soil Organic Matter. SOM has a higher CEC than other soil types like sand and clay.

Soil Organic Carbon have a negative charge so they attract positively charged nutritious minerals like Calcium, Potassium and Magnesium. Similarly, SOC improves soil’s water retention capacity.

Soil Organic Carbon particles have a negative charge so they bind positively charged nutrious minerals.

More carbon resides in soil than in the atmosphere and all plant life combined

There are 2,500 billion tons of carbon in soil, compared with 800 billion tons in the atmosphere and 560 billion tons in plant and animal life.

Soil organic carbon (SOC) is a measurable component of soil organic matter. Organic matter makes up just 2–10% of most soil’s mass and has an important role in the physical, chemical and biological function of agricultural soils.

Sequestering carbon in SOC is seen as one way to mitigate climate change by reducing atmospheric carbon dioxide. The argument is that small increases of SOC over very large areas in agricultural and pastoral lands will significantly reduce atmospheric carbon dioxide.

It has been estimated that agricultural soils have lost 42–78 Pg of carbon relative to their pre-agricultural state. The transfer of soil organic carbon to the atmosphere is a major driver behind the climate change, but also represents an opportunity for managing current greenhouse gas emissions through carbon sequestration.

The loss of SOC has negatively affected soil health and increases our reliance on inorganic fertilizers to maintain crop productivity.

A large number of soil functions that are critical for crop and pasture production, including nutrient and pH buffering, water retention, soil structural stability, and higher agronomic efficiency with related to soil’s capacity to exchange nutrients are all positively associated with greater SOC levels.

Global human-induced soil degradation (FAO)

Grasslands as a carbon sink

Unlike forests, grasslands sequester most of their carbon underground, while forests store it mostly in woody biomass and leaves.

Forests have traditionally been viewed as robust carbon (C) sinks; however, extreme heat-waves, drought and wildfire have increased tree mortality, particularly in widespread semi-arid regions, which account for ~41% of Earth’s land surface.

A study by Californian University shows that grasslands are a more resilient C sink than forests in response to 21st century changes in climate, with implications for designing climate-smart Cap and Trade offset policies. (Dass, Pawlok & Houlton, Benjamin & Wang, Yingping & Warlind, David, 2018)

The resilience of grasslands to rising temperatures, drought and fire, coupled with the preferential banking of carbon to below ground sinks, helps to preserve sequestered terrestrial carbon and prevent it from re-entering the atmosphere.

Let microbes to do the hard work

Grasslands sequester large amounts of SOC because of a high below ground carbon allocation, root turnover, and rhizo deposition. Grassland gross primary production (GPP) is the major natural soil carbon input and has been estimated at 31.3 Pg C yr−1 for tropical savannas and grasslands, and to 8.5 Pg C yr−1 for temperate grasslands and shrublands. (Lorenz & Lal, 2018)

Possible inputs of below ground C include: (i) incorporated surface plant residues, (ii) plant root litter and rhizodeposition, (iii) dung and urine of grazing animals, and (iv) black carbon (BC) in fire-affected grasslands. Grazing management must be targeted toward SOC sequestration due to the large global grazing land area and potential for considerable rates of increase in SOC stock. (Lorenz & Lal, 2018)

How is Carbon stored in the Soil (University of Waikato, 2015)