Imam Ammar Amonette, of the Islamic Center of Virginia, said the move made "no sense whatsoever".

BBC: Tamerlan Tsarnaev's secret Virginia burial upsets locals

Dr Amonette's estimate is that 50 tonnes per hectare a figure larger than that used in most of the experiments conducted so far could go into soils without harming productivity.

ECONOMIST: Biochar could enrich soils and cut greenhouse gases as well

Taking all these things together the burial of the charcoal and the substitution for fossil fuels of the heat, gas and oil produced by its manufacture Johannes Lehmann of Cornell University and Jim Amonette of the Pacific Northwest National Laboratory in Washington state suggest that a reduction of between one and two gigatonnes of carbon-emission a year might be achievable.

ECONOMIST: Biochar could enrich soils and cut greenhouse gases as well