Wednesday, May 16, 2007

Alkaline Soils - Terra Preta solution

Regarding application of Terra Preta to the Alkaline soils, yesterday I had been to Kothur Village, a V & A Programme village in Semi-arid environment (for more information see ).

I explained the farmers regarding the use and application of Terra Preta for treating the alkaline soils. Before that some char pieces were brought for demonstrating the use and good qualities of char. Using the high resolution imageries of Google the fields with intense alkaline soils were identified. From those selected areas four farmers have come forward to try this method in their half to one acre size fields. Regarding the application, as there is abundant availability of Prosopis in the village, this is an easy method for them. The logistics and the cost of char was discussed, they were able to sell char @Rs. 0.2$ (USD) per kg. For applying about 1500 kgs of Char per acre, it would cost them about Rs. 300$ (USD). Which seems to be on the higher side for the poor farmers, so another alternative was making charcoal from the thin stems of Prosopis a wasted product in the charcoal making process and there was plenty of such dry twigs / stems of Prosopis available. Some farmers in the recent past trying to reclaim their Prosopis lands have used machinery and there are lots of heavy uprooted root stocks, with soil attached. They are burning such root stocks in the respective fields. This kind of burnt material consists of

  1. partial biochar
  2. Char,
  3. well burnt soil and
  4. plenty of ash

The farmers have agreed to put this resultant material in their fields, which is of no cost and available in plenty. I am only hopeful that the above resultant material is acidic and would improve the soil quality. As the farmers have not started the process yet, the timely advice from you all would be helpful.

The soil testing results and the suggested recommendations (draft) are seen in this link:


Dr. N. Sai Bhaskar Reddy said...

On 16/05/07, Christoph Steiner
> I have my doubts that "Terra Preta" is the solution for all
> constraints. Terra Preta was created to overcome the environmental
> constraints in the Amazon. Alkaline soils are not among them, the
> is the case.
> Ash and most charcoal are alkaline. Therefore I recommend being
> But anyway it is very interesting to look what effect charcoal
> to alkaline soils have. For my knowledge this was not studied yet and
> alkalinity is a widespread problem.
> C. Steiner

Dr. N. Sai Bhaskar Reddy said...

Dear Kevin,

Thank you very much for your valuable suggestion. This area is drought prone
and receiving very less rain fall year after year, there is a total
reduction of 20 centimeters (from 80 cms in 1950's to < 60 cms presently).
The Climate Change / variability, over extraction of groundwater and
application of complex chemical fertilizers and high temperature conditions,
and seasonal rainfall, extraction of groundwater for paddy and flood
irrigation, etc. resulted in the alkalinity of the soils.

The option of using ever depleting meager groundwater resources for treating
the alkaline soils is a rare option.

The traditionally people were using Gypsum / sand / green mulching methods
to treat alkaline soils. And also traditionally people believed that the
burning of the crop residue in the fields benefited their soil. Some farmers
also brought the ash+soil from the Brick making kilns and they were
applying. That could be the reason why when discussed farmers were ready to
apply the combination of (partial biochar+char+ash+burnt soil) for their
alkaline soils. Probably the resultant soil could(?) be with pH neutral (?)
+ phosphorous, calcium and iron, more soil moisture retention capability,
changing the texture of the soil to soft (rather than hard kankar), etc.
These are the expectations, more over the green mulching and addition of
little gypsum will be encouraged. I believe Terra Preta could be a solution
for alkaline soils too (?). Thanking you once again.

Dr. N. Sai Bhaskar Reddy

On 5/16/07, Kevin Chisholm kchisholm at wrote:
> Dear Dr. Reddy
> Pardon my brashness, but I can't see any way that Terra Preta would help
> with your alkaline soil problem. Can you propose a rational mechanism by
> which the Terra Preta could help?
> My understanding is that you can reclaim alkaline soils using gypsum as
> soil treatment.
> The basic reaction is:
> CaSO4 + Na2CO3 --> CaCO3 + Na2SO4
> The thing is that the Na2SO4 is more soluble than Na2CO3 and can be
> washed away from the soil. Actually, I don't know if it is so much a
> solubility issue, as it is a "bound" versus "unbound" issue.
> Hopefully, the Farmers have sufficient water that they can "irrigate
> away" the Na2SO4. If not, it might be possible to add the gypsum one
> year, and then develop a washing process to lift soil into a tankage
> system for agitation and washing.
> Best wishes,
> Kevin

Philip Small said...

My guess is that some types of char, used in conjunction with other management tools, may benefit some alkaline soil conditions.

Some chars are more alkaline than others. Low alkalinity char would be important. In sodic soils with pH buffered to pH 9.2 by sodium bicarbonate, some less alkaline char types could of benefit.

Philip Small said...

An example of variations in charcoal pH from a pdf:

Two charcoals from Norit America are Gro-safe and Darco S51. When Gro-safe is mixed with tap water at the rate of 10 lb to 15 gallons the pH is 10.95. Darco S51 mixed at this rate has a pH of 6.59. The Gro-safe charcoal is a H-type charcoal that was oxidized at 800 -1000 oC. Basic surface oxides are formed on the edges. Thus the charcoal will raise the pH of a aqueous solution when it is added to the solution. Darco S51 is an acidic charcoal, or L-type charcoal, which is oxidized at 200 - 400 oC. Acidic surface oxides are formed, and they will lower the pH of an aqueous solution.

arclein said...

has anyone tried to do this in a pot?

The ability of charcoal to adsorb just about anything makes me very cautious in predicting adherence to the normal chemical pathways.

Also a dressing of bio char in the thin growing layer might allow a separation of the alkaline into the subsoil. A perfectly happy solution.

I address carbonization extensively in my own blog:

I am keen on seeing practical ways of producing char in the field.

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