A new comment on the post #2450 “Terra Preta Soil Technology (Google / iMechanica)”
http://desertification.wordpress.com/2008/02/24/terra-preta-soil-technology-google-imechanica/
Author : Erich J. Knight
Comment:
Tony Lovell of Soil Carbon P/L in Australia estimates that by actively supporting regrowth of vegetation in damaged ecosystems, billions of tons of carbon dioxide can be sequestered from the atmosphere. “Determining how much carbon dioxide (CO2) can physically be consumed from the atmosphere? As the planet has 7.8 billion tonnes of carbon dioxide in circulation for each 1 ppm of atmospheric CO2, and there are 5 billion hectares of inappropriately managed or unmanaged, desertifying savannahs on the Earth (which on empirical evidence we contend to be the case), the question that should sensibly be asked is: How much carbon dioxide would be absorbed if policies were put in place (in Australia and elsewhere) that caused the focus of on-ground management to be deliberately directed towards the widespread consumption of cyclical GHGs within the currently under-utilised savannah lands?
Consumption of CO2 per hectare
* One hectare is 10,000 sq. metres. If a hectare of soil 33.5 cm deep, with a bulk density of 1.4 tonnes per cubic metre is considered, there is a soil mass per hectare of about 4,700 tonnes.
* If appropriate management practices were adopted and these practices achieved and sustained a 1% increase in soil organic matter (SOM)6, then 47 tonnes of SOM per hectare will be added to organic matter stocks held below the soil surface
* This 47 tonnes of SOM will contain approximately 27 tonnes of Soil Carbon (ie 47 tonnes at 58% Carbon) per hectare
* In the absence of other inputs this Carbon may only be derived from the atmosphere via the natural function known as the photo-synthetic process. To place approximately 27 tonnes of Soil Carbon per hectare into the soil, approximately 100 tonnes of carbon dioxide must be consumed out of the atmosphere by photosynthesis
* A 1% change in soil organic matter across 5 billion hectares will sequester 500 billion tonnes of physical CO2
Converting global Soil Carbon capacity to ppm of atmospheric GHGs
1. Every 1% increase in retained SOM within the topmost 33.5 cm of the soil must capture and hold approximately 100 tonnes per hectare of atmospheric carbon dioxide (the variability in the equation being due only to the soil bulk density). We submit that under determined, appropriate management, that this is readily achievable within a very few years
2. For each 1% increase in SOM achieved on the 5 billion hectares there will be removed 64 ppm of carbon dioxide from atmospheric circulation (500,000,000,000 tonnes CO2 / 7,800,000,000 tonnes per ppm = 64 ppm).
3. Soil Organic Matter is the plant material released into the soil during the natural phases of plant growth. It includes root material sloughed off below the soil surface and plant litter carried into the soil by microbes, insects and rainfall
4. Soil Carbon is the elemental carbon contained within Soil Organic Matter (SOM).
5. One tonne of CO2 contains 12/44 units of carbon (ie 0.27 tonnes of carbon per tonne of CO2.). Therefore 27 tonnes of carbon sequesters 27/0.27 = 100 tonnes CO2 (rounded). NB Carbon atomic weight 12, oxygen atomic weight 16 ie CO2 = 12+(16+16) = 44
The global opportunity and numbers
It appears that the pre-industrial level of atmospheric carbon dioxide was 280ppm, and that globally we are now at 455ppm, and heading towards 550ppm. To get from 550ppm back to 280ppm, 270ppm must be removed. Globally, a 4.2% increase in SOM would potentially reverse the expected situation. In any case, any form of determined management will substantially reduce the now crippling legacy loadings in the atmosphere.
Erich J. Knight
1047 Dave Berry Rd.
McGaheysville, VA. 22840
540-289-9750
shengar@aol.com
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