Stability of soil organic matter in Terra Preta soils

Bruno Glaser, Institute of Soil Science, University of Bayreuth, D-95440 Bayreuth, Germany. email: bruno.glaser@uni-bayreuth.de

 

Ludwig Haumaier,Georg Guggenberger and Wolfgang Zech

 

Summary

In the Brazilian Amazon basin there are small spots of sustainable and very fertile anthropogenic black earth soils of precolumbian origin (Terra Preta do Indio) within the typical rather infertile Oxisol landscape.The Terra Preta soils are characterized by a higher cation exchange capacity, higher phosphorus levels and a higher content of soil organic matter (SOM). The accumulation of organic matter in soils of the humid tropics seems quite paradox because of the optimum conditions of degradation.

There is evidence that Black Carbon (BC) is decisive for sustainability of these Terra Preta soils. To prove this hypothesis we developed a method based on marker substances exclusively derived from charring. We used benzene polycarboxylic acids (BPCA) as specific indicators for burning. After oxidation with nitric acid, extraction from soil, adequate sample cleanup and derivatization, BPCA were identified and quantified with gas liquid chromatography and flame ionization detection.

We show that the stablility of SOM in Terra Preta soils derives to a large extent from residues of incomplete combustion of organic material. Slow oxidation of BC creates carboxylic groups which increase the cation exchange capacity and therefore the soil fertility.

 

Keywords:

soil organic matter; black carbon; stability; Terra Preta; anthropogenic soil; soil fertility;