Soil represents a reservoir that can hold at least twice as much carbon as the atmosphere. The carbon is mainly sequestered through plant photosynthesis, and historically, the emergence of deep-rooted trees and flowering plants has resulted in huge reductions of atmospheric CO2.

The majority of agricultural crops have short root systems that only penetrate about a metre into the soil. Professor Douglas Kell of the University of Manchester argues that doubling root biomass by breeding crops with longer, bushier root systems that penetrate a further metre into the soil could potentially harvest twice as much carbon from the atmosphere. In addition, soil structure could be improved and crops would be more resistant to drought and flooding. Crop yields could also rise due to better water and nutrient retention.

In order to support his argument, Kell designed a carbon calculator to quantify the potential benefits. He found that, depending on the time it takes for roots to break down, replacing all of the world’s current crops with varieties whose roots penetrate a metre deeper could double carbon sequestration.

‘What matters is not so much what is happening now as what might be achieved with suitable breeding of plants with deep and reasonably long-lived roots,’ Kell said. ‘Many such plants exist, but have not been bred for agriculture.      

Anna Gibbney
October 2011