Friday, August 8, 2008




Terra preta research inspired the development of a revolutionary technology that can have tremendous impact on rural livelihoods as well as carbon sequestration.

Charcoal burial goes back 2,000 years or more in Brazil. Manmade soils at many sites there, known as “terra preta” (Portuguese for “black earth”), are still the most productive of perhaps any on earth. It builds on the application of stable organic matter in the form of bio-char (biomass-derived black carbon or charcoal) in conjunction with nutrient additions. This bio-char is very stable, provides and retains nutrients for millennia, as seen in Terra Preta.

Terra Preta was first described by Charles Hartt in 1874

The application of bio-char improves soil fertility by two mechanisms: (1) by adding nutrients to soil (such as K, to a limited extent P and micronutrients); (2) by retaining nutrients from other sources including nutrients from the soil itself. The main advantage is the second, the enhanced nutrient retention mechanism. In most situations, the biochar additions have a net positive effect on crop growth only if nutrients from other sources such as inorganic or organic fertilizers are applied as well.


Creates space for soil microbes
Activates the mycorrhizae
Protect roots of seedlings
The use of charcoal prevents the leaching of nutrients out of the soil,
increase the available nutrients for plant growth,
enhance nutrient uptake from soil,
provide minerals like Ca, K, Mg etc.,
Reduce the amount of fertilizer required.
Improves water permeability, water retention potential
Decreases N2O and CH4 emissions from soil, thus further reducing GHG emissions.
Charcoal addition in soil helps in carbon sequestration.
Reduced soil bulk density
Sequestered large amounts of carbon
Increased soil respiration


Most of the charcoal produced in developing countries is produced in earth kilns and the conversion factor can vary from about 10 m3 per tonne of charcoal up to 27 m3 per tonne depending on the moisture content, species and skill of the operator. Therefore, in order to determine the roundwood equivalent, the production method should be known - earth, portable steel kiln, brick kiln, a retort, etc.
Conversion factors per tonne of charcoal sold. 1 (Average volume 1.4 m3/t at 15% m.c.) 2
1 It is assumed that the fines are briquetted in the retort.
2 With softwoods about 60 percent, more volume is required per tonne of charcoal and with dense hardwoods such as mangrove about 30 percent less volume is required.
Units m3 n e
Moisture Content
Kiln type 15% 20% 40% 60% 80% 100%
Earth kiln 10 13 16 21 24 27
Portable steel 6 7 9 13 15 16
Brick kiln 6 6 7 10 11 12
Retort 4.5 4.5 5 7 8 9

In India, fuelwood, crop residues and animal manure are the dominant biomass fuels, which are mostly used in the rural areas, at very low efficiencies. The total potential of energy from these sources in 1997 is estimated to be equivalent to 5.14 EJ, which amounts to a little more than a-third of the total fossil fuel use in India. The energy potential in 2010 is estimated to be about 8.26 EJ.
HYPOTHESIS ABOUT BIOCHAR: If BC is not being removed from the soil as fast as it is being produced, might it simply be accumulating there.

Lal (2005) estimates the world production of crop residues to be 4x109Mgyr-1.

Taking a mean carbon content of 48% (see section 1.2.1) and a pyrolysis yield of 48% of this carbon in the char (Lehmann et al 2006, 413) this translates to a maximum possible 1PgCyr-1 from crop residues. The actual potential will be lower than this, as not all crop residues will be suitable or recoverable, some of this total biomass will be required for incorporation into soil, and there will other competing demands for useful residues such as straw.

A maximum of 1 PgCyr-1 biochar might be produced from agricultural residues (if all current global agricultural residues were converted to biochar). In practice, this figure will be constrained by cost, suitability of different residues, requirements to incorporate residues into the soil, and other competing demands. How much biochar might be produced from agricultural residues once such constraints have been taken into account is a matter for further research.

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

Lehmann et al. (2006) estimated that a total of 9.5 billion tons of carbon could potentially be stored in soils by the year 2100 using a wide variety of biochar application programs. Once equipped with a better understanding of this potential synergism and the mechanisms that drive it, we could utilize biochar/mycorrhizae interactions for sequestration of carbon in soils to contribute to climate change mitigation. This interaction could also be harnessed for the restoration of disturbed ecosystems, the reclamation of sites contaminated by industrial pollution and mine wastes, increasing fertilizer use efficiencies (with all associated economic and environmental benefits) and the development of methods for attaining increased crop yields from sustainable agricultural activities. 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
Burning of crops in the field


India produces annually about 800 million tonnes of agricultural waste and about 200 million tonnes of urban organic waste. From 6 major crops like rice, wheat, sugarcane, g.nut, mustard and cotton 69.9 million tons of crop residue is produced annually in India.

Burning residue releases large amounts of carbon dioxide into the atmosphere. This emission of high levels of carbon dioxide is not ecologically friendly, creates pollution and also contributes towards global warming. Burning the residue also means that the soil will be left bare. The soil will then be exposed to rainfall impact and the baking sun, which can cause erosion and the rapid loss of nutrients. The soil will quickly lose its fertility, especially soil organic carbon needed for sustainable production. The ashes can be distributed over the soil to improve soil fertility. However, the ashes do not contain the same level of nutrients as the original crop residues and are easily blown or washed away. With burning, pests and diseases that are harboring in the residues will be destroyed; however, all beneficial organisms in the soil residues will be destroyed as well!

Fire can remove residue that hinders crop growth, limits quality or carries disease. Across the world the use of fire as an agricultural tool is being discouraged as concerns mount about greenhouse gases and air quality. Burning crop residue adds carbon, nitrogen and hydrocarbons to the air. Fire consumes organic matter and may reduce total nitrogen available for plant growth on the site. Fire can also damage growing crops. Farmers must carefully consider the costs of using fire. In most cases alternative crop residue management methods make more sense.

Why Do Farmers Burn?
The majority of farmers do not burn. They prefer to handle straw in other ways, for example, by tilling it into the soil, and by chopping and spreading the straw so it does not plug up seeding equipment. It has been estimated that in Manitoba, province-wide, only about five percent of producers burn unwanted straw.

Burning is one way to dispose of the straw left after harvest so fields can be made ready for seeding the following spring.
However, some farmers find it difficult to deal with straw in the normal ways. For example, a bumper crop can leave a tremendous amount of straw, which can be very difficult to work into the soil or spread evenly across the field. Rainy weather after harvest can leave fields too wet to till.
Burning straw is considered a low-cost solution alternative to tilling in the straw. Under such circumstances, farmers may feel they have no choice but to burn the straw.
Why is Burning More Common in Certain Areas?
In some areas, soil has a high clay content. This type of soil is prone to drainage and compaction problems, which can make burning appear to be a more attractive option than tillage. Certain areas, such as the clay soils around Winnipeg, produce high yielding crops, which means a lot of straw is also produced. This makes it more difficult to incorporate the straw into the soil. For this reason, it has become a traditional practice for farmers to burn in some areas. New technology and innovations, however, can make it possible to incorporate all residue into the soil.
Why Some Years are Worse Than Others
When good growing conditions occur (plenty of moisture and heat), grain crops are heavier than usual, so plenty of straw can be left after harvest. As well, heavy summer rains can leave fields too wet to till (as was the case in 2004). A late harvest can further complicate matters, leaving less time for farmers to till their fields before freeze-up. With a late harvest season, farmers are often concerned that they will not be able to complete proper tillage operations in the fall. If producers are unable to complete tillage operations in the fall, seeding can be delayed in the spring, which has the potential to negatively impact the next season’s crop. As a result, many choose burning as a residue management option.
In Manitoba, our crop production season is incredibly variable from one year to the next. For example, one year producers may have their crops seeded early and harvest may be well underway by mid-August. In other years crops may be seeded late or weather conditions may be such (cooler than normal temperatures), that harvest is delayed into late October and early November. This variability that exists within any growing season puts pressures on producers to complete their work as quickly as possible.
Gupta says that the environmental benefit is just as high as the cost-savings. “Leaving a protective blanket of leaves, stems and stalks from the pervious crop on the surface is actually better for the long terms health of the crops and soil.” Residues provide a natural herbicide, retain nutrients in soil and moderate soil temperature. “By burning the residue, farmers were actually stripping the soil of microbes and moisture that are essential to a crop's long terms health,” he added.
Most double-crop grain farmers in South Asia remove or burn crop residue to facilitate seedbed preparation and to avoid possible yield reductions. This results in loss of soil organic matter (SOM) and nutrients. In this study, we determined whether incorporating wheat (Triticum aestivum L.) residue, rice (Oryza sativa L.) residue, and sesbania (Sesbania aculeta L.) green manure with urea fertilizer N in a rice–wheat cropping system can improve grain yields, N use efficiency, and SOM. We incorporated wheat residue (6 Mg ha-1, C/N = 94), rice residue (6 Mg ha-1, C/N = 63), or both, with and without green manure (20 or 40 Mg fresh ha-1, C/N = 19), in a field experiment with irrigated rice and wheat grown each year in rotation on a Tolewal sandy loam (Typic Ustochrept) in the Punjab of India. Rice and wheat residue did not affect grain yields of wheat and rice, but residue incorporation did result in reduced recovery efficiency of urea N and green manure N. Rice production was greater with wheat residue incorporation when an average of 86 kg N ha-1 of a prescribed 120 kg N ha-1 dose was applied as green manure N and the balance as urea N vs. 120 kg urea N ha-1 alone. Despite wider C/N than rice residue, wheat residue additions to flooded rice resulted in greater C sequestration in soil than with rice residue or 40 Mg green manure ha-1. These results demonstrate that a green manure crop and/or incorporating crop residue in a rice–wheat system has potential to increase SOM while maintaining high grain yields.

Units conversion
PgC/yr - petagram of carbon per year.
1 PETAGRAM (Pg) = 1000000000000 KILOGRAMS


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