Black carbon in soils: The use of benzene polycarboxylic acids as specific indicators

Bruno Glaser, Ludwig Haumaier, Georg Guggenberger and Wolfgang Zech

Institute of Soil Science, University of Bayreuth, 95440 Germany. Fax: ++49-921-552246. Email: bruno.glaser@uni-bayreuth.de

Mitteilungen der Deutschen Bodenkundlichen Gesellschaft (1997) 85: 237 - 240

1. Introduction

Black carbon (BC) is formed during incomplete combustion of biomass. Being highly resistant to microbial and chemical oxidation, it is considered to be a significant sink in the global carbon cycle. Most likely, it is also a source of stable aromatic carbon in soils.

The 'Terra Preta' phenomenon: a model for sustainable agriculture in the humid tropics
Bruno Glaser, Ludwig Haumaier, Georg Guggenberger, Wolfgang Zech
Journal Naturwissenschaften,Springer Berlin/Heidelberg
Issue Volume 88, Number 1 / February, 2001


Many soils of the lowland humid tropics are thought to be too infertile to support sustainable agriculture. However, there is strong evidence that permanent or semi-permanent agriculture can itself create sustainably fertile soils known as 'Terra Preta' soils. These soils not only contain higher concentrations of nutrients such as nitrogen, phosphorus, potassium and calcium, but also greater amounts of stable soil organic matter. Frequent findings of charcoal and highly aromatic humic substances suggest that residues of incomplete combustion of organic material (black carbon) are a key factor in the persistence of soil organic matter in these soils. Our investigations showed that 'Terra Preta' soils contained up to 70 times more black carbon than the surrounding soils. Due to its polycyclic aromatic structure, black carbon is chemically and microbially stable and persists in the environment over centuries. Oxidation during this time produces carboxylic groups on the edges of the aromatic backbone, which increases its nutrient-holding capacity. We conclude that black carbon can act as a significant carbon sink and is a key factor for sustainable and fertile soils, especially in the humid tropics.

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