Unlocking the soil's potential with biochar

Biochar, the residue created by burning biomass, has been increasingly recognised for its remarkable ability to improve soil fertility and store carbon. Kobus Stoop, director of Cape Town-based Senfore Soil Conditioning, spoke to Glenneis Kriel about the substance and its potential for agriculture.

- Glenneis Kriel

What is biochar? 

Biochar is produced during the pyrolysis of wood or farm waste, a process that applies heat without oxygen. Biochar is created at a much higher temperature than ordinary charcoal, making it more stable and porous, and allowing it to remain in the soil for hundreds of years. Ordinary charcoal decomposes within a couple of years, depending on climatic conditions.

Who came up with the idea of using it to enrich the soil? 

It’s thought to have originated around 2 000 years ago in the Amazon basin, when people produced it by charring organic waste in primitive ovens with a low supply of oxygen.

This special charcoal was added to the soil, resulting in patches of rich soil that retained their fertility for centuries and later became known as terra preta (Portuguese for ‘black earth’). It’s said that a crop planted in terra preta can produce a yield up to four times greater than in any other soil, and local farmers who mine it claim that a given volume can double in size within 20 years if left undisturbed.

What is the chemical mechanism for its effectiveness? 

Biochar is a negatively charged compound, and as such helps to improve the cation exchange capacity of the soil. This in turn increases the retention of soil nutrients and reduces run-off. The current hype surrounding it centres on its ability to draw carbon from the atmosphere and serve as a carbon sink in the soil.