Saving the World, Destroying the Rainforest

Soil scientists and organic gardening advocates, like those at the Rodale Institute, have for decades propounded the importance of organic matter in soils. Organic materials promote good soil structures and help retain nutrients that would otherwise be leached away.

It turns out, though, that the best organic soil component had not been properly appreciated. It's charcoal. Charcoal retains nutrients even better than the traditional organic materials derived from plant litter, manure, or compost. It binds phosphorus, which those others don't do. And, best of all, charcoal is stable in soils -- even tropical soils -- for centuries or millenia. The other organic materials quickly decompose, especially under tropical conditions.

These properties are crucially important for the highly leached and oxidized soils of the tropics. Much of the Amazon basin had been thought to be useless for agriculture because of depleted, acid soils lacked nutrients and would too quickly lose any that were applied. But within the past decade it was increasingly realized that this didn't have to be the case, and that, in actuality, pre-Colombian cultures had successfully terraformed and farmed large areas of the Amazon. Their technique, which caused the formation of so called Terra Preta de Indio, or 'indian dark earths', involved the long term addition and accumulation of charcoal and other organic materials in Amazonian soils. The resulting dark soils have remained fertile even after centuries of cultivation by farmers ignorant of its origin.

Addition of charcoal to soils is now being promoted as part of a carbon-negative biomass energy system. Biomass, when heated in anoxic conditions, pyrolyzes to make charcoal and a hydrogen-rich gas. About half the carbon ends up in the charcoal, some of which can then be added back to the soil. This carbon would accumulate over many cycles, making the soil better with time instead of depleting it.

I do worry, however, that all this will have a side effect that the advocates don't mention. If the Amazon can be made productive, there will be increasing incentive to exploit it. The tropics can be farmed year round and have plenty of water and sunlight. Already Brazil is becoming one of the lowest cost producers of grain and soybeans in the world. If biofuels become globally important as oil substitites, economic forces will drive the conversion of the rain forest to energy plantations. Sure, the Amazon could be farmed with small-scale, organic, ecologically sensitive methods. So could the US midwest -- but it largely isn't. And given how the forests of the temperate zones were converted wholesale to farmland, the previously developed countries won't be able to object without hypocrisy.