Microscopic characterisation of synthetic Terra Preta

Abstract

Amazonian Dark Earths (Terra Preta) are anthropogenic soils with high organic carbon content and the ability to sustain higher fertility than adjacent, intensely weathered, acidic soils. Consequently, the microstructural development of biochar–mineral complexes, termed synthetic Terra Preta (STP), has been investigated. Here, biochar–mineral complexes are produced at elevated temperatures to mimic the structure of Terra Preta. These materials, if added to soils, may then also improve fertility. The raw materials used in STP were organic biowaste, such as sawdust, chicken manure, and blood and bone, and inorganic minerals such as kaolinite, bentonite, and cement kiln dust (which consists mainly of calcite). The STP samples were characterised using X-ray photoelectron spectroscopy, nuclear magnetic resonance, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and associated microchemical analytical methods, to gain an understanding of the interactions that occurred during processing between the organic and inorganic phases. The STP specimens exhibited microstructures that closely resemble Terra Preta. SEM and TEM revealed a complex aggregation of phases, together with evidence of the interfacial reactions, especially at higher processing temperatures. It is anticipated then that STP may be as effective in promoting plant growth and in sequestering carbon as Terra Preta