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How much energy does soil hold?
How much energy does soil hold?
We can work out the amount of energy now stored in soil, that is driving the natural world. The soil worldwide stores an estimated 42.5 exajoules of energy in the form of organic carbon. This energy originates from the process of photosynthesis, where plants capture solar energy and convert it into chemical energy, which is then transferred to the soil through decomposition and nutrient cycling. The maintenance and enhancement of this energy reservoir are crucial for soil health, ecosystem functioning, and the global carbon cycle.
Energy Stored in Soil:
mostly in the form of organic matter like decomposed plants and animals.
fuel that keeps soil healthy and fertile, supporting plant growth and microbial activity.
How Much Energy?
Estimate that the world's soils contain about 2,500 gigatons of organic carbon.
Is like having around 42.5 exajoules of energy stored in the soil. 1 EJ = a billion billion (10^18) joules!
How Did This Energy Get There?
Plants and Photosynthesis:
Decomposition by Organisms:
Accumulation Over Time:
Forms of energy in soil
Forms of energy in soil
Organic Matter:
Soil organic matter (SOM) is a major reservoir of stored energy, primarily in the form of carbon compounds derived from dead plant and animal material.
This organic matter includes decomposing leaves, roots, microorganisms, and humus.
Chemical Energy:
Chemical energy is stored in the bonds of organic molecules within the soil.
Nutrients like nitrogen, phosphorus, and potassium are part of this chemical energy reserve, vital for plant growth.
Microbial Biomass:
Microorganisms in the soil, such as bacteria and fungi, contribute to the energy pool by breaking down organic matter and facilitating nutrient cycling.
Estimation of energy in SOM
Estimation of energy in SOM
To provide a rough estimate, we can look at the carbon content of SOM (soil organic matter) as a proxy for stored energy.
Global Soil Carbon Pool:
According to various estimates, the world's soils contain about 2,500 gigatons (Gt) of organic carbon in the top meter of soil.
Organic carbon represents a significant energy reservoir, as the energy content of organic matter is approximately 55-75% of its dry weight.
Energy Calculation:
The energy content of organic carbon can be estimated using its calorific value, which is around 17 megajoules (MJ) per kilogram of carbon.
Using this value, we can estimate the total energy stored in soil organic carbon.
Calculation:
Calculation:
Total Organic Carbon=2,500 Gt
Energy Content per kg of Carbon=17 MJMJ 1 Gt=1012 kg
Total Energy=2,500×1012 kg×17 =42,500×1012 MJ
=42.5×1015 MJ
=42.5 exajoules (EJ)
How did this energy get there?
How did this energy get there?
Photosynthesis:
The primary source of energy in soil comes from photosynthesis, where plants convert solar energy into chemical energy stored in organic compounds.
When plants die and decompose, this stored energy is transferred to the soil as organic matter.
Decomposition:
Soil microorganisms decompose organic matter, releasing nutrients and energy stored in plant and animal residues.
This process transforms complex organic molecules into simpler compounds, contributing to the soil organic carbon pool.
Soil Formation Processes:
Over millennia, plant and animal material have accumulated and decomposed, gradually increasing the soil organic matter content.
Geological and climatic factors also influence the accumulation and preservation of organic carbon in soils
Coal Comparison
Coal Comparison
Can we use the amount of energy caught with coal formation to calculate with what is now decomposed - to humus?
Most geologists consider coal was formed when peat bogs, having limited anaerobic decomposition, got squashed under the tectonic plates moving about.
There is an 'evolutionary lag' hypothesis that the plants did not break down because of lignin in the trees made decomposition difficult, and that it was not till later that white rot fungi (WRF).
Coal formed over a relatively short period, while humus formation has been going on hundreds of millions of years
Some people - and that used to include me - believed that the development of various decomposition processes saw an end to possible coal formation.
When the trees died in Carboniferoous times, "the bacteria, fungi, and other microbes that today would have chewed the dead wood into smaller and smaller bits were missing, they were not yet present. Trees would fall and not decompose back ” (Ward and Kirschvink 2015).
Now, I believe the main reason peat accumulated in Carboniferous times was that any decomposition in that swamp/bog was anaerobic which wasn't very efficient - much the same as today.
Good decomposition needs a mixture of aerobic and anaerobic.
Coal formation
Coal formation
Coal is a sedimentary rock formed from the remains of plant material that accumulated in swampy environments over millions of years.
Coal formation typically requires anaerobic conditions, which means that the plant material is buried in an environment with limited or no oxygen availability.
Over time, the plant material undergoes biochemical and physical changes due to the pressure and heat from overlying sediment layers. This process, known as coalification, results in the transformation of plant matter into various types of coal, such as lignite, bituminous coal, and anthracite.
Coal formation occurs over geologic time scales (millions of years) and is associated with specific depositional environments, such as ancient swamps and marshes.
Humus Formation
Humus Formation
Humus is the organic component of soil formed from the decomposition of plant and animal material.
Humus formation occurs in soil environments where organic matter accumulates and undergoes decomposition by soil micro- & meso-organisms.
Unlike coal formation, humus formation primarily occurs in aerobic conditions, where oxygen is available to support microbial activity and decomposition processes.
Humus is relatively short-lived compared to coal and undergoes continuous turnover within the soil ecosystem. It plays essential roles in soil fertility, nutrient cycling, and soil structure improvement.
Coal to Humus
Coal to Humus
Complex organic compounds, like cellulose and lignin, are difficult to break down, but that is usually more efficiently and effectively done in aerobic circumstances. In anaerobic environments, slower decomposition rates allow for the accumulation of these stable organic materials. In Carboniferous period, massive peat bogs developed with anaerobic decomposition that was slow and limited. They were later crushed and compacted into coal.
There are similar sized peat bogs today in various places, like Siberia, showing this limited anaerobic decomposition is still around. We are just waiting for the appropriate tectonic plates to move to make coal. Coal and soil are separate.
Yet the decomposition process has evolved since the Carboniferous period, so that much more organic detritus is broken down - there is much more to go at, and this is being done more effectively. Much now ends up as humus. The interesting question is what that can tell us about the energy saved in the soil systems. A lot of energy has to go into soil to maintain the metabolism and hold it together, otherwise it disintegrates in disorder, according to the 2nd law of thermodynamics. But how much energy?
Coal Energy
Coal Energy
According to the World Coal Association, global coal reserves were estimated to be around 1.1 trillion metric tons as of 2022. Coal has an energy content of 24,000 exajoules (EJ).
Coal reserves are barely half of that energy presently in the soil which has been calculated at 42.5 exajoules.
Since the mid-19th century, the cumulative global consumption of fossil fuels is around 1,500 exajoules.
When considering soil as a closed system for the purpose of explaining entropy, in reality, soil is an open system that exchanges energy and matter with its surroundings. Here’s how the energy inputs affect entropy:
Sunlight and Photosynthesis:
Sunlight is a primary energy input for soil ecosystems. Plants use sunlight to perform photosynthesis, converting light energy into chemical energy stored in organic matter.
This process creates an organized structure (organic matter) from less organized components (CO2 and water), effectively reducing entropy locally.
Organic Matter Decomposition:
When plants die, their organic matter is decomposed by microorganisms. This process releases energy stored in the organic matter and transforms it into simpler compounds, increasing the entropy of the soil system.
However, the energy released during decomposition is used by soil organisms for metabolic processes, which can lead to the formation of humus and other stable organic compounds that contribute to soil structure and fertility.
We do not see it, measure it or bother to look after that energy in soil. We take it for granted, planting annual monocrop after annual monocrop for generations. That is what fools us. But then - quite suddenly the energy used to maintain the metabolism - and hence balance of organisms - is used up - and the soil falls apart and is washed to sea or dries out. Dirt: Erosion of Civilisations Montgomery "traces the role of soil use and abuse in the history of Mesopotamia, Ancient Greece, the Roman Empire, China, European colonialism" Next time will be our civilisation.
Ponder this: Much of modern civilisation has been built on coal with energy stored from over 300mya. Our civilisation is also built on the energy driving soil metabolism. We also use the energy stored in the soil that runs soil metabolism. For generations everything is alright, until that healthy metabolism dies - and it can go quite quickly.
Ponder this: Much of modern civilisation has been built on coal with energy stored from over 300mya. Our civilisation is also built on the energy driving soil metabolism. We also use the energy stored in the soil that runs soil metabolism. For generations everything is alright, until that healthy metabolism dies - and it can go quite quickly.
Seagulls are not as daft as we are
Energy drives the soil, so the more emnergy the more metaboism to keep soil healthy and prevent erosion and desertification.
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